I need some help to make a decision about an in-floor heating system for a house I’m designing. This house will be the first I have ever built for myself and I hope to stay in it for a long time to come. We want it right.
The house will be ICF construction, very tight and it will be compact, nearly a square floor plan to get the most volume for the least wall. I calculate the total heat loss at -5*F to be about 17 500 BTU/h. Not much, though that’s taking no account of gains and losses from ventilation or opening a door to let the dam dog out or from solar gains and radiant losses through the windows or of waste heat from cooking. Nor do I have any idea how to account for the long lag time before outside temp changes show up inside a concrete house or what effect that will have on the dynamics of the house.
The floors will be concrete, 4″ in the basement slab and a 1 ½” overpour on the other two levels with ½” Rehau pipe embedded and a pump for each zone rather than zone valves. The zones will be the sunny side and the shady side of the house on all three levels where the partitioning makes that work. Finish floors will all be stained concrete or tile.
The hard part for me in my ignorance is deciding what the heat source should be.
One of the proposals I have is for a 9kw Seisco in-line heater with Tekmar controls set up to take advantage of the lower electricity rates available in off-peak hours. The pusher for this system says it will be vastly cheaper to run because it heats only the amount of water needed and only when it is needed. No stand-by losses. He also says the sophisticated controls will better anticipate temp changes by monitoring both indoor and outdoor temperatures and the result will be a much more even temperature in the house and greater comfort. He also predicts that water heaters would need to be replaced after about 7 or 8 years and that cost should be included in the reckoning somewhere. The life span of the Seisco is unknown but thought to be long.
The other proposal consists of two 60 gal electric hot water heaters and a fancy mixing valve to cut the output temperature down. The man selling this says I can still go on the peak/off-peak electricity rate program because that is a power company ,metering thing and nothing to do with the heating system design. He predicts the heating demand will not begin until hours after sunset anyway and, as for stand-by losses, that heat is staying indoors and can’t be considered a total loss. An intake from the ventilator in the heater space will help distribute that heat. He says there will be temperature swings with this system. It will more often be too hot than too cool, for reasons I don’t understand. But, he says that a system like this can be tuned to even things out by somebody with a little knowledge (that’s me) who is aware of how the house performs.
This second system costs about $3 000 less than the first, but money isn’t the only issue here. I am concerned mainly about how the house will feel though I am also concerned about two money issues: Is there a possibility I might end up buying both systems, one after the other because, (A) with the Seisco, when I need a replacement part in ten years it will be obsolete and out of production and (B) with the water heaters, what is the chance they won’t keep us comfortable anyway?
Anybody got any ideas how the performance of these two systems might compare in real life? Mongo?
To give you an idea about how a concrete house works around here, on Monday I was talking to the owner of one I built last year. Her house is exposed to every wind that blows but she said that neither wind nor outside temperature make any difference – if the sun shines, her furnace does not run. Neither her house nor mine were designed to maximize the passive solar heating, because there is a basic incompatibility between passive solar and hydronic floor heat and we both want the warm floors.
Ron
Replies
To qualify for off-peak rates, don't you have to have an alternate-fuel, automatic back up source? That's what my PoCo requires. So I plan to put in two water heaters, an electric WH run on off-peak rates (3.7 cents/KWH in my case) with a propane WH plumbed in series...outputs of both run through a heat exchanger for the RFH and through a mixing valve for DHW. Leaves it up to me as to which fuel source I'll use.
My designer has done several of these and says it works well.
I'm curious about why you are opting for pumps versus zone valves, and also your heat loss calculation...shouldn't the loss calc INCLUDE the losses through the windows?
BTW...have you browsed through these yet? Lots of good informaiton on both of theses forums:
http://www.radiantpanelassociation.org/i4a/pages/index.cfm?pageid=1
http://forums.invision.net/index.cfm?CFApp=2
Edited 4/1/2004 9:01 am ET by johnnyd
>To qualify for off-peak rates, don't you have to have an alternate-fuel, automatic back up source?
Not where I am (Western NC). They include a penalty for on-peak use that whoops you upside the head sufficiently that you pay attention if you're not set up right to control usage.
Here, (Tri-County Co-Op) they supply a cut-over deal that is radio controlled that shuts down the off-peak users. You need to wire it with a separate meter and base.
At the end of the month they subtract the off-peak reading from the entrance meter readng to come up with your bill.
Gentlemen,
You've given me a lot to think about but I feel like I'm getting farther away from a decision.
Johnnyd, I took account of the static state heat losses from the windows but there are also losses due to heat radiating out through the glass that I just don't know how to calculate. A normal heat loss calc is a pretty limited thing all in all. I wanted pumps rather than zone valves n=because they cost just about the same and seem to run everlasting without trouble. Thanks for the links. I have looked at the radiant panel association site and found it useful.
Bill, the time of use rate plan here in Nova Scotia is a daily one. The normal rate is $0.08/kw. On the time of use plan the off peak rate is $0.04 and the peak use rate is $0.12. I have chosen electric because of the low capital cost. A ground source heat pump is out of the question for such a small demand. Air source needs a back-up heating system anyway. An oil burner costs more to begin with and then you have to buy a tank and a chimney. Propane costs the earth to run. We have no nat gas. I haven't projected the operating costs because I have to heat it anyway, the real life dynamics are a mystery to me and we also have a wood stove we're going to use with wood cut on the property. My dilemma is how to choose a system that will leave us comfortable for a reasonable cost.
Cloud, the incompatibility between hydronic RFH and a passive solar house is that you can't store your solar gain if your thermal mass has already been heated by some other method. If you can't store the heat you do not have a passive solar house. There is a local architect who specializes in passive solar houses in which he uses floor slabs up to 10" thick for storage by lacing them with air ducts. You pump the air 24/7. It carries the heat into the slab during the day and out of the slab at night. Very elegant. You are certainly right about the heat demand and its relationship to orientation and glazing and weather. But while your heat pump might produce more BTU per kw becaue it is a mechanical transfer of heat from one location to another, electric resistance heaters are 100% efficient. One kw of electric energy in equals one kw of heat energy out.
David, I'll check into the tubing size. There seem to be very few people around who know anything about the thermodynamics of high mass houses. I'll testify that I'm not one of them, but ask me again in a couple of years. I have been thinking about how to combine the floor heating and domestic uses but the proble is I need the storage capacity in order to take advantage of the lower night time electricity rate. I'm thinking the heat storage capacity of the floors themselves won't be enough unless I keep a few tanks of heated water around, but I simply don't know if it will be or not.
I think you a probably right about the importance of the controls. I am going to investigate upgrading the water heater system with controls better able to anticipate heat demand.
Thanks
Ron
>But while your heat pump might produce more BTU per kw becaue it is a mechanical transfer of heat from one location to another, electric resistance heaters are 100% efficient. One kw of electric energy in equals one kw of heat energy out.
I got in trouble with someone here once for using the word efficiency in the wrong way, so I won't touch on that or its relevance. I need btus to heat the house. I have kw coming in. My gshp draws 13.9 amps to produce 48,000+ btu/h. That's $95/month if run 24/7. My supplemental elec water heater draws 19 amps for an additional 12,000 btu/h. That's be $400+ if I used elec water heaters run 24/7 to match the btu output of the gshp, assuming I remember the calcs I once did. I dunno from efficiency, but it's a more effective use of my wallet by faaaar. :)
Ron, 100% capture from electric resistance is about 33% as efficient as a good heat pump in its design temp range. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Paul: You've made an important point that needs to be emphasized: a heat pump does just what the name would imply- it uses mechanical energy to PUMP HEAT from a cold place to a hotter place. In this case, the cold place is the outdoors (either the air or the ground) and the hotter place is your house.
If you put 1 watt of electricity into a resistance heater, you get one watt of heat out of it. 100% efficiency in converting electricity to heat.
If you put 1 watt of electricity into a HEAT PUMP, you get 2-4 watts of heat into your home (depending on the outdoor temperature). By the same measure as you used to judge the resistance heater, that's 200-400% efficiency at converting electricity to heat in your home. The WORST it can do is about 100% better than a resistance heater! Any "efficiency losses" from friction or eddy currents in the motor etc. turn into heat, which if the heat pump itself is located in your house, ends up heating your house too!
Yeah, I know that off-peak electrical power is being offered at cheaper rates right now, but that's to discourage peak consumption- not to encourage people to find new ways to waste off-peak electricity! It burns my butt to hear of people using electric resistance heaters to heat their entire homes, when the electricity they're using is produced from burning fossil fuels! Where do you think the electricity was coming from, man? In Nova Scotia, where the original poster lives, they're burning either oil or coal to make the vast majority of that electricity- they're a long way from the Quebec hydro projects or Ontario's nukes. So if you look at it from the point of view of efficiency, think of the two options this way:
Option 1: burn fuel to heat water or air to heat your house
Option 2: burn fuel to make steam to drive a turbine to drive an alternator to drive a distribution system which radiates a good portion of the energy off into space as heat and radio waves, to drive a transformer to feed electricity to a resistance heater to make: HEAT! The electrical generation step alone is max 35% efficient, and another good chunk of that is lost before it gets to your house!
In terms of "efficiency", there's no comparison between these two! And remember, this overall efficiency from fuel to heat is the real measure of how much impact your heating system is having on the world- and ultimately your pocketbook.
Electricity is "work on tap"- it's energy which is readily converted to any other form you need it in: heat, light or mechanical work. Don't waste it running heaters- if you must rely on electricity, at least use it to run a heat pump! Or better still, if you're in Nova Scotia, buy an oil-fired boiler and use that to drive your radiant heating AND your hot water (since natural gas isn't an option in your area). If you can work a woodstove into the picture, that would be nice too- make use of some of NS's renewable resources.
Molten, no argument from me. I too find many people confusing the 100% eff of ele without an understanding of a heat pump function. Many don't realize that a HP (air to air) simply air conditions the out doors and transfers the heat inside in the winter.
Re your nick name: were or are you in the metal business? I was at Reynolds Aluminum for years, did our paths cross? PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Paul, I understand the efficiency of heat pumps, but isn't there a curve where you get diminishing returns when the delta between outside and inside temps is too big?
If your climate is out of the curve for efficient air-to-air and you have limited space/conditions for a trench-based heat source, and well digging regulations make it really expensive to drill for a well water heat source, you're left with the old natural gas/oil/propane/electric decision.
John, a heat pump is not the best answer for all climates, but where only ele is available, in usually wins easily. Yes, there is a point where backup heat is often necessary, usually in the low 30 deg range. However, the trigger point is usually set by the house thermostat. When the heat pump can not keep the indoor temp to within 2 deg of set point, the backup heat cuts in. Usually this is electric resistance coils. Another condition that triggers the backup heat is when the condensor goes into the defrost cycle. A large enough capacity HP could heat your house without backup heat in most cases, but the system would be grossly oversized when it came to the air conditioning season. Therefore, most installations are a compromize between sizing for heat with enough ele strip heaters, and still being a logical capacity for AC.
Living where the winter temp is well below freezing most or all winter would not be a great place to have a HP. I would want a fuel system and a backup, so that if the primary failed, you wouldn't freeze the house or your toes. Paul
Edit, John, Regardless of heat source, I think the most effective delivery of heat to a home is RFH, but up front cost is high, and the system somewhat redundant if AC forced air is also needed. I will be installing a hybrid, ie., some rooms will get RFH, and other rooms, especially heavy wall to wall carpet, will rely on forced air heat (floor mounted supplies), and all rooms will get forced air AC.
Energy Consultant and author of Practical Energy Cost Reduction for the Home
Edited 4/2/2004 1:54 pm ET by Paul Hayden
Thanks for your advice.
My design temperature is -10*F. Dual fuel rate .035/KWH. House designed and sited to stay comfortable w/o AC. Guess I've ruled out HP. Plan is to heat water for RFH with primary electric and secondary propane. Sleeper/Al plate/PEX system goes on sub-floor within next 60 days.
Guess I'll have a few months to make final decision regarding heat source.
Hi Paul (my name's Paul too...)
My handle is not related to my profession- that's chemical engineering, pilot plant design and fabrication mostly as well as some water treatment equipment development/design and some site investigation/remediation work in a past life. The username is related to the most unusual of my my hobbies. I built a little reverbratory propane-fired furnace and use it to melt bronze scrap to make sand castings- mostly hardware for my woodworking projects. I'm not a master pattern-maker or moulder, so it's nothing fine and fancy in the casting department- just raw, rough and heavy stuff, like heavy drawer pulls, knobs and candlesticks. I like the look and texture of the stuff after you bead blast or take a power wire brush to it right out of the sand. One of these days I may buy some oilsand and do some finer stuff, but right now it's silica sand and kitty litter, which works and is cheap as, well, dirt.
I do a little aluminum casting (old barbeques and window frames are the source material mostly), but I've had no dealings with Reynolds aside from buying a little aluminum foil from them via the grocery store.
Keep up the good posts!
Thanks, Paul for the bio. Didn't mean to pry, but thought we might have crossed paths. I have visited aluminum casting plants all over the world, engine blocks, wheels even thin walled 5'x10'x 1/4" building wall panels cast in sand but with a vacuum pulled at the same time as the pour.
Have you tried some lost foam casting for your cabinent pulls?
Sounds like you enjoy a neat hobbie. Best wishes. If I can help in your home energy needs, don't hesitate to post. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Hey Paul- don't worry, you weren't prying.
Lost foam is something I'd like to try, but I'm worried about the unholy stink it would make. Got to keep the neighbours happy, and the fact that I fixed up the derelict house on the block and brought up their property values will be lost on them if they start seeing a plume of putrid black smoke rising out of the chimney of my shed every weekend!
The reason I'm not doing lost wax investment casting is that I'm lazy. I'd have to carve the pattern in wax, make a latex mold to permit me to make copies of the pattern, and then invest each one. Sand's a pain in the butt, but less bother than going through all that!
When I get closer to building my addition and proper shop, I'll be flooding the place with questions- and you'll be one of the guys I hit up most often. I'm just trying to pay the debt forward, by adding my two cents worth whenever I feel it can be of benefit!
"I'm thinking the heat storage capacity of the floors themselves won't be enough unless I keep a few tanks of heated water around"
True. And you want have warm/hot water available to heat the slab up. BUt let's run the numbers:
Useable BTUs in the floor are going be something like the (very massive) floor cooling from about 90F to 80F. 1000 sq ft (a guess) x 0.33 ft x 150 pounds/cu ft x 0.22 heat capacity x 10F = 108,900 BTU or 6 hours worth.
Versus two 60 gallon HWHs = 2 x 60 gallons x 8.3 pounds/gal x 1.0 heat capacity x (140F-90F) = 49,800 BTU = 3 hours worth. So if you are counting on the water to carry you through the day, figure on more water.
Admittedly, most days won't be as low as your design temp (that 17,000 BTU/hour demand) so often the water would last twice as long. But even so, I think you'd want 2X to 4X as much water.David Thomas Overlooking Cook Inlet in Kenai, Alaska
First of all I would find out the EXTAC details of what plan(s) that power company has for electric heat.
There are a number of different ones. Where I am it is strictly based on time of year, not time of day, and you you get a break (about 10%) on all electricity used during the winter if you have primary electric heat.
And I would find out how high the rates go during the high power time if you need to add heat then. And how long of time period the off peak hours are.
Without this information anything else is meaningless.
And what are you electric rates and projected operating cost?
And what part of the country are you in?
Have you thought about using a heat pump. I know that ground souce heat pumps ('geothermal') can do this, but they are big dollar items. There are also air to water heat pumps, but I am not sure.
As to your underlying question, can the thermomass of the house hold the tempature during the off times I have no idea.
But I find that something strange in the two proposals and you need to ask them some more questions.
#1 with the boiler has no storage, but he said that it would maintain constant temps. His he basing that on the thermomass of the building or that it would still operate sometimes during the peak time period.
#2 has storage in the tanks. But he claims that you will have some temp swings unless you really tune the system well. Why? Is he talking about just the problems with fine tuning a radiant heat system in a house with a large thermomass. That would be the same with #1 or a gas fired boiler or etc.
And with the storage with the 2 tanks you you could store up all of the energy at night and if you needed more during the day draw from the tanks and not go to high demand electric.
I've hydronic in the basement slab and staple up on the first floor of a 1200 sq ft extension to my house. Since January I've been running it on one 60 gal water heater with a water coil hooked into a woodstove. I keep the woodstove going 24/7 by loading it at 0630 , 1830 and 2130
The house has ICF foundation 2x6 walls with foam insulation, but lots of window area.
I'm using 1 pump for the hot water circulation, 4 loops of an adjustable manifold and another pump for the circuit to the woodstove.
I've got a mixing valve to reduce the water temperature through the pipes. It was no problem to install or adjust.
So the water heater cost about 300$cdn to install. I've run a gas line near to it so down the road I can switch if I want to.
The system balance easily enough, so far.
Ontario is just getting into residential off peak power. I would think that you would have to overheat quite a bit during the off peak time to keep the house comfortable until the off peak, power on , period starts again
I'm using the electric as back up. My first electrical bill should arrive this week. I'll let you know how it worked out cost wise.
Just a note. The hydronic system's primary purpose in my addition is to warm the floors. The prime heat/ AC will be from gas fired hot air and central air. In this municipality if electric heat is seen to be the prime heat source the building inspection requirements become more stringent.An ex-boat builder treading water!
Edited 4/1/2004 10:31 am ET by Bob
>because there is a basic incompatibility between passive solar and hydronic floor heat and we both want the warm floors.
How so? Not my experience.
>He predicts the heating demand will not begin until hours after sunset anyway
Don't think I buy that. You're building a hi-mass house, and I have one, too. It's not quite so cut-and-dried as sun up, no need to heat, sun down, heat. I find that the need to heat is fairly constant, but much lower than other houses. A lot depends on your glazing and orientation to the sun. And on overcast or snowy days, with no solar gain, the system will need to provide btus, be/c the house will be losing btus, regardless of time of day. Elec water heaters have a bad ratio be/t btu and kw. My ground source heat pump, by contrast, has a better than 4x better ratio.
Edited 4/1/2004 12:46 pm ET by Cloud Hidden
As Cloud said, in a high-mass house, when to add heat is not simple (I've got one too). If the nights are cold, you want the slab to be hot then. Which means you should have been adding heat quite a while back. Came morning sunshine, you don't need the heat the way you do on a cloudy day.
"Outdoor reset" (goes by other names too) looks at the outdoor temp (usually to set mixing valve setting) and the trend in outdoor temp (to start the RFH early). Those smarter controls (on any heat source) do a lot to even out temps inside.
My house also needs 18,000 BTU/hour, but at -40F. So I run it off a gas hot water heater. Why aren't you using dino-juice (fuel oil) or dino-farts? e.g. propane or natural gas? Those new-fangled electrons are cheaper in a very few locations, so maybe it makes sense, but post your kwh price to be sure.
1/2" in a 4 and 5.5" can be a problem. It takes a while to heat up a slab with 3 gpm in the loop. One thing you MUST do is keep down the loop length. 150' or less. Yes, it comes in 250' rolls, but that is only okay for staple-up or 1.5" slabs. Not for 4" slabs. Either go to 3/4" or use short tubing lengths.
I'd look for a way to combine your domestic hot water heating with RFH water heating. Why buy extra appliances and take more floor space to do the same thing?
Again - smart controls and an intelligent tubing layout is more important that the particular type of heater. As long as the heater makes enough BTU/hour, your comfort will hinge on the design and controls.
Ron,
What Cloud and David Thomas are telling you is very much in accordance with my own experience as well. If you have the time and inclination, it would be worth re-thinking some of your assumptions.
I have built four ICF homes, two of which were passive solar, both of these have radiant (hydronic in-flooor) heat, one inside a 4" concrete slab, one under brick on sand. According to the homeowners, the thermal performance of both buildings exceeds any of our expectations. Both of these homes are in 6,001 degree-day climate. The more recent of the two needs the heat to be turned on from 5:30a to 7a when the outside temperature goes below 15 degrees F. That's it.
Actually, there is quite a bit of knowledge in the building community about mass-compensated thermal performace. While it is complex, it is not difficult. I would start by looking at the website for Sandia National Labs or the National Renewable Energy Lab.
http://www.nrel.gov/index.html
If gas is an option, you might consider one of the combo units, it's a boiler and domestic water heater in one. Very efficient, and you can't use hot water faster than this thing will heat it.
If solar is an option in your climate, there are a few ways to make this work great in an ICF home. First up would be a solar collector and heat exchanger to pre-heat the return water from your heating system. I used to have one, it cut my heat bill in half.
Second that comes to mind is a Trombe wall. I don't know if they are suitable where you live, if so, I've got them worked out, at least when it comes to ICF. I have seen some incredible failures when it comes to these things, and was the most skeptical person you'll ever meet, but the homeowner insisted, and by golly, we made it work in spades.
Next up is R-foil. There will be a raftload of people who can't wait to explain to you why this can't possibly work, but it does. Just one of those things that works in practice but not in theory. <G>
Good luck, please post more questions, and especially share with us what you learn.
DRC
Dave, I do indeed have the time and inclination to learn a bit or I wouldn't have started this. There may be a lot of knowledge about high mass building performance in the building community but there certainly is not inside my own cranium. I have built several ICF houses too and their performance astonishes me but I have never designed one before. They were all designed by architects and I had no responsibility for the heating system other than ensuring the installation was done to a reasonable standard. Solar collection is a good option around here but I'm thinking I'll get more bang for the buck if I use collectors on the DHW in that they'll be in use year round. I plan to build my own. You'll probably read about that here when it happens. Thanks for the link. I'll look at that this evening. Another exciting Friday night coming up.
David, the heat storage capacity of the floors will be close to 8 hours worth at the design temp of -5*F. The storage capacity ofthe tanks would be about 4 hours worth. A normal average winter temperature is closer to -15*F so I should have a bit of a cushion and I do count on both solar gain and supplemental heat from burning wood.
Paul, I have to agree with you about the environmental consequences of using electricity. You forgot to include in your list the vast amounts of oil used in finding oil, carrying it to the refinery, refining it, transporting it to the consumer. I have heard that up to 15% of all petroleum production goes into petroleum production. There are environmental consequences to just about every decision we make. I have decided to try to minimize the total energy use of this house period, though there will be a huge energy expenditure to build it - concrete is a very energy expensive product.
Thanks
Ron
Good on ye' for cutting down the energy costs as best you can- we've all got to do our part. Using a fuel to heat the house directly rather than wasting electricity to do the job will help- and probably save you money in the long term.
Numbers I've heard put the figure on finished fuel production nearer to 30% than to your 15% of feed being used up in the discovery, recovery and refining processes. For sources like oilsands etc., the numbers are even worse. As we run out of the Middle East oil which more or less runs out of the ground under its own pressure, we get pushed to more and more use of harder-to-produce fuels, and these all generate yet more CO2 per gallon of gas or fuel oil in the tank. So the only long-term solution is conservation through more efficient use of what we have now, and more investment in renewable energy.
As far as concrete is concerned, it's definitely an energy-intensive product- but it's also a durable one, so don't feel so bad. If we smartened up and permitted the cement kilns to use old car tires and organic hazardous waste (old oil contaminated with PCBs etc.) to supplement their fuel use, like they do in Europe, they could cut down the fuel use considerably while solving some environmental problems at the same time. You'd have a hard time designing a better chlorinated waste incinerator than a cement kiln- it has about ten times the hot gas residence time of a purpose-built waste incinerator, and it has all that calcium sitting there waiting to gobble up the chlorine and HCl as soon as it's generated so it can't hang around and make chlorinated dioxins and furans in the flue gas. And we need to add a little calcium chloride to our cement up here in Canada anyway for the colder parts of the season, or so I'm told, so it wouldn't have a detrimental effect on the product quality either.
Johnnyd, I like the idea of using waste products to operate cement kilns. Up in Cape Breton there has been talk about burning the contents of the tar ponds in Sydney so as to use the heat for something like cement kilns.Though there is a certain amount of hysteria that surfaces whenever the tar ponds are mentioned certain people are starting to think of them as a resource. (The tar ponds in Sydney are lagoons holding the waste products of a century or so of coke production. Estimates are of a million or so tons of hydrocarbons with various noxious substances mixed in. The most polluted site in Canada.)
Paul, I've seen the shower heat recovery units advertised in FHB. They're really worth it?
VaTom, I am going to stick with electric resistance for DHW. With a solar collector I don't think DHW will break the bank. It doesn't hurt that much right now and I don't think our habits will change much with a new house. Saturday night bath night, same old same old.
Ron
"fuel production nearer to 30% than to your 15% of feed being used up in the discovery, recovery and refining processes"
I'd agree with that range for, as you said, regular oil production. Pumping it, secondary and teritary recovery (steam, pressure, CO2), transporting, refining it, distributing it.
Less for N.G. Much more for oil sands, oil shale. And higher if you count the bombs, soldiers, etc to protect our "national" (oil) interests.
What burns my butt (or rather, does not heat my butt, alas) is the lack of domestic-sized co-gen. N.G. for most, fuel oil for anyone comes to their house. So why not burn it to generate your own electricity at 35% effieciency and use the 65% waste heat for domestic hot water and space heating? A water heater, an alternator, and a lawnmower can each be sold for about $100. So why can't the combination cost $300? Yes, I know, economies of scale, getting the ball rolling, etc. But wouldn't it be cool if the tremendous values represented by HWH and auto parts could be duplicated in co-gen systems?David Thomas Overlooking Cook Inlet in Kenai, Alaska
David- we agree about co-gen. We're energy gluttons and energy morons here in North America, because energy's been cheap enough for so long that we could afford to be. Co-gen is much more widely used in Europe. Here, we're mostly just throwing that low-grade heat down the drain (or using it to heat up the atmosphere...) instead of using it to offset other fuel consumption, and it's a crying shame. The biggest single reason is that owners are capital-cost sensitive and don't give heavy enough weighting to on-going operating costs- and the virtuous ones like the original poster here are few and far between- most owners just don't even consider the environmental consequences of their choices. All they care about is money out of pocket right now. Short-sighted thinking leads to unpleasant consequences down the road- it's true in carpentry, in engineering and in all other aspects of life as far as I can tell! Unfortunately, when too many people make the same bad short-term decisions about energy use, even we few who care about the bigger picture have to suffer their consequences!
"Short-sighted thinking leads to unpleasant consequences down the road"
Like teenagers and the three "I"s? That teenagers believe themselves to be infallible, immortal and infertile. And they act accordingly.
Most homeowner believe they have enough Insualtion, Insurance, solar Input and Intelligence when really they are lacking.
But with people carrying 18% balances on their credit cards, it is easy to see why even a no-brainer like compact-fluorescents are a hard sell.
Edit: Are we Chem Engs the only ones that had present worth and operating costs explained to us? Or were we the only ones listening?
David Thomas Overlooking Cook Inlet in Kenai, Alaska
Edited 4/8/2004 5:23 pm ET by David Thomas
David: I've often wondered that too. Why can't people figure out that operating costs are going to come out of their pockets too, just like the capital costs? And forever afterward, too!
Ron, while you are designing your efficient home, take a look at GFX heat reclaimers for your shower drain. You can Google the subject, and cost benefit looks good. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Solar collection is a good option around here but I'm thinking I'll get more bang for the buck if I use collectors on the DHW in that they'll be in use year round.
Ron, if your climate includes ac and/or dehumidification you might consider a heat pump water heater. Installed one here last year in our considerably higher mass house. In addition to supplying hot water roughly 3x more efficiently than an electric heater, the byproduct is cool, dry air. Kinda like ac, but free. Our payback was slightly over 1 season for the hpwh, but even at normal prices would have been 4 years of seasonal use.
You can read more at: http://www.pnl.gov/fta/3_res.htm#manu
You've gotten some good advice on the heating system. Efficiency is good. If you make your house efficient enough, you won't need one. That's where the real savings occur.
PAHS Designer/Builder- Bury it!
"You've gotten some good advice on the heating system. Efficiency is good. If you make your house efficient enough, you won't need one. That's where the real savings occur."
I agree, and I think this observation is essential to the design of homes that depend upon mass-compensated thermal performance. To design only for a worst-case scenario (the coldest week of the year) can distract a designer from recognizing the natural economy of modulating the diurnal temperature swing that, in most climates, is surprisingly accomodating to our needs.
A little solar home humor there. Probably too dry, sorry, couldn't resist. <G>
Since about 1972 we've focused on R-value, which is not a bad thing, but it can obscure the fact that there are many other design approaches that will get us to the desired end i.e. a comfortable, durable home that does not require a lot of fossil-fuel input.
I like ICF for a lot of reasons, not the least of which is the R-value of the foam and the ease with which we can built an amazingly tight home that is in no immediate danger of rotting of having a mold problem inside the walls. But foremost for me as a fan of solar heat is the fact that the walls can easily weigh a hundred tons.
Add it all up and you get a home that is very resistant to thermal change. If it tends to be comfortable, it tends to stay that way all the time.
So back to the original question; If I remember correctly, the radiant heat was not intended as the primary heat source. Any reason why not? Seems to me that at a design target of -10, an ICF home with the solar exposures worked out wouldn't need any more than a warm floor every now and then.
DRC
Dave, the RFH will be the primary heat source. My dilemma is in choosing the "kettle" that puts the heat into the floor and the control system for it. I haven't yet started clearing the land so it will be three months or so before I need to make this decision.
I'm surprised to discover how hard it is and how much I have yet to learn about houses. I've only been at this since 1970 you see.
Ron, my mistake, and my apologies. I somehow managed to mix Bob's post (#4 in this thread) into your original question.
I think you've got a remarkable opportunity here in the form of CloudHidden and Dave Thomas. Both of these guys know their stuff. It's one thing to have a few solar/high-mass success stories (that's me), it's quite another thing to be able to design and accurately predict the performance of a fairly complex and fully integrated building system (that's them).
"I'm surprised to discover how hard it is and how much I have yet to learn about houses. I've only been at this since 1970 you see."
Well, you've got me beat by a few years. It all strikes me the same way, though. Apparently, you and I are in good company -- if the quote attributed to Michealangelo late in his life ("Ancora Imparo" or "I am still learning") is truly his, then I don't feel so bad about resigning myself to the spectre of feeling like the older I get, the less I know.
Maybe the only really useful observation I have in response to your initial query is that passive solar and high mass can indeed work beautifully together. It's a design problem that must not be taken lightly, of course, as the consequences of a bad design will be serious, but the resources are available.
From my perspective, the direction David Thonas and Cloud are suggesting is sound. With enough focus in the design phase on passive solar and overall envelope efficiency, the additional inputs required can be minimized to the point where the decision about how to power the system become less crucial to the overall success.
DRC
Dave I assure you no apology is called for .
I'm not really such an old timer as all that. I've done other things than carpentry in the years since my first job with a renovator in 1970, but I have 20 years at this racket.
Lately, I have been taking an evening course from the architect I mentioned above who specializes in passive solar design and I'm very impressed with his techniques. I might just mention to him that he should check out BT. He says his houses get 50% of their heat from the sun with no additional costs. I believe it.
It is his contention that storage of the solar gain is an essential condition for a passive solar home and that hydronic RFH is therefore not compatible with passive solar because his thermal mass is the floor. If you heat it by burning oil you can't store the solar gain there. It makes perfect sense to me.
I'm still going to heat my floors with water and I expect to heat that water with electricity. Maybe the next house will be different.
I think you are quite right about the power plant becoming less of an issue if you can reduce your demand upon it and that's the direction I hope I have been heading with ICF construction, compact design and some attention paid to siting and orientation.
Ron
>It is his contention that storage of the solar gain is an essential condition for a passive solar home and that hydronic RFH is therefore not compatible with passive solar because his thermal mass is the floor.
The concrete in the house shell and the slab are both part of the mass that "stores" and benefits from solar gain. To the extent that the slab temperature rises through solar gain, it just means fewer btus you'll have to toss in there via other means.
Assume that you get 100% of the gain you need from the sun, and that your slab and walls are sufficient to maintain the temp from sundown till the next day when the solar gain exceeds the house's heat loss. That would mean that you didn't need to run the boiler/water heater for those hours. Hooray.
Then assume you get a snowstorm for 2 days. Either your outdoor reset or your slab sensor or your regular t-stat will recognize the need for heat and supply it via the boiler/water heater.
Solar gain reduces need for oil/electricity. When there's no sun, the oil/elec takes over. I don't see where there's an incompatibility.
"Solar gain reduces need for oil/electricity. When there's no sun, the oil/elec takes over. I don't see where there's an incompatibility."
That's how I see it, too. I've been trying to figure out how the architect came to his position, and I can't yet.
On that note, a client (who was by far more saavy about solar than me)asked about running the radiant loop so that the return ran through the part of the slab that was best situated for solar gain, thereby somewhat heating the return water before it got to the boiler. I wish he had asked me about this before we poured the floor, I would like to have tried it on that particular house.
"The concrete in the house shell and the slab are both part of the mass that "stores" and benefits from solar gain. To the extent that the slab temperature rises through solar gain, it just means fewer btus you'll have to toss in there via other means."
That's how I finally got Trombe walls to work. In both bathrooms and the living room (on a southwest exposure) I interrupted the ICF by the dimension of a standard patio replacement IG panel plus 7" eash way. Poured that part of the wall with the concrete flush to the interior face of the ICF, held the pour back about 2-1/2" from the outside. Stuccoed the exterior face of the wall black.
Fabricated a 1-1/2" x 3-1/2" steel square-tube frame (duplicating a 2x4 frame laid flat against the wall), set the glass on the steel frame with Shur-Seal. Vented the top and bottom ever so slightly to get rid of condensation, packed vent with fine scren to keep bugs out.
Because this +/- 8-inch thick 3-0 x 6-8 slab is poured continuous with the wall, a lot of the heat of the day gets sucked right into the wall. A lot comes through the tiled face, as well. It really feels good after the sun goes down, and dries the towels in the bathroom in no time.
If we're storing heat, modulating the diurnal and annual (thank you <G>) swing, and the house remains comfortable all the time, we've done well. I see no reason to confine the design to the floor.
The only possible objection I can think of from the architect is that a high-mass passive solar home with radiant heat might not be real comfortable if the temperature changes suddenly and often. I can see his point, but most folks I know of just put in a woodstove. That seems to take care of it.
DRC
>The only possible objection I can think of from the architect is that a high-mass passive solar home with radiant heat might not be real comfortable if the temperature changes suddenly and often.
I wonder if he's talking about the risk of overshooting or undershooting? I had undershooting by my 500 sf glazing at first. The sun would raise the ambient temp and kick the tstat off, and then the sun would go down and the ambient temp would drop fairly fast, but the slab would be slower to respond. Took me a year to figure that out. But, the solution was not to forego one technology or the other, but to find a way to get them into homeostasis so to speak (or the term I coined here: domeostasis!). Two options. One could be to use a slab temp sensor rather than an ambient temp sensor. The other was to find the right tstat setting. Eventually I found that instead of setting the temp to 68, as in the rest of the house, I set that one space to 71/72. The solar gain was not therefore as quick to cause that temp rise, and so the slab did not stop heating just be/c the sun warmed the air near the tstat. That's all I needed to balance the room, and I haven't had to adjust anything since, didn't need a slab sensor, and have neither over- nor undershooting.
It does take some effort and thought to balance a passive solar system, but in my experience it is quite compatible with rfh in a high-mass building.
Thanks for the Trombe wall description.
"Solar gain reduces need for oil/electricity. When there's no sun, the oil/elec takes over. I don't see where there's an incompatibility."
That's how I see it, too. I've been trying to figure out how the architect came to his position, and I can't yet.
I don't know his thinking either, but if he's thinking that the earth under the slab is part of the storage system, ala PAHS, the insulation normally placed under a radiant slab would be a hindrance. Clearly, confining the insulation to the perimeter would work better than total isolation from the earth.
The only possible objection I can think of from the architect is that a high-mass passive solar home with radiant heat might not be real comfortable if the temperature changes suddenly and often.
Temperature changing suddenly and often is the hallmark of a low mass, excessive glass home. A 4º diurnal swing would be unusual for us.
Interesting what you did for a Trombe wall. No noticeable chilliness from having an uninsulated wall portion after the wall cools off? As in, why not do the whole southern exposure that way? You aren't ducting air around the wall, simply relying on conduction through the wall?
PAHS Designer/Builder- Bury it!
"Interesting what you did for a Trombe wall. No noticeable chilliness from having an uninsulated wall portion after the wall cools off?"
Not a bit. I think the insulated glass takes care of a lot of that, I suppose the balance is taken care of by the tons of warm concrete inside the ICF walls that are connected to the Trombe. Remember, the Trombe is cast continuous with the ICF.
"As in, why not do the whole southern exposure that way? You aren't ducting air around the wall, simply relying on conduction through the wall?"
Nope, no ducting of air at all. In my experience, that's the problem. You are correct, I'm relying strictly on the conduction through the wall.
As for "why not do the whole exposure?", I don't know -- I never thought about it. I think I would defer to someone with more knowledge than me on this one. Seems to me that someone who really knew their stuff could design this so that it would work.
What do you think?
DRC
[edited to add quotation marks]
Edited 4/3/2004 7:50 pm ET by Dave Crosby
Seems to me that someone who really knew their stuff could design this so that it would work.
What do you think?
I remember seeing more than a few (similar to yours) Trombe walls in the Denver area when I lived there (pre low e). Yours was by far the most glowing account. So I presumed that the lack of exterior insulation was a problem. Clearly, moveable exterior insulation, like Steve Baer (Zomeworks) was using, would work. We're too lazy (and windy) for that. We expect to wake up, like this am, with 35º outside and the wind howling, to 66º with the stove cold for days.
For me to do heat loss calculations is a not-small undertaking. Manually, with the aid of an old text. Went through it for my next house, oriented for view, as it's very different from this one, also PAHS (of course). Substantially larger and including an indoor pool to heat. Active solar system that needed to be sized. We're about through burning wood (not that we burn much now), although there will be a wood-fired backup boiler. But rather than RFH, to get back to the thread, I opted for cast radiators. We like them, kind of fits with the high mass house. Bearing in mind that we have no need for rapid heating with a house that averages 70º (by itself) on an annual basis. I'll undoubtedly have to go through Cloud's learning curve to find the correct thermostat settings.
Somebody here must have a simple program to plug numbers into. Went to download a recommended program awhile back. Turned out to be a 4-5 hr dialup download. I pulled the plug. But I build very few houses.
The large majority of my next house's heat loss will be through my low e glass. More glass doesn't help. Will the increased solar gain on your concrete offset that? Don't know. Definitely going to be climate dependent. Did you catch Junkhound mentioning that south-facing low e was a net heating loss for him (compared to plain glass)? One thing that probably does help you is that you have thinner walls? My southern walls are 12" thick.
Are you one of those builders that David was complaining about who don't do heating calculations? <G> PAHS Designer/Builder- Bury it!
"Are you one of those builders that David was complaining about who don't do heating calculations? <G> "
Yep, that would be me. <G> And unapologetically, I might add. Here's why;
A few years ago I worked as a site super for a builder who was deeply devoted to the cause, and went so far as to hire a full-time energy design consultant. This guy used computer programs to try to design solar and/or energy efficient homes. All very commendable, yes?
The result was disappointing at best. It seems that the behavior we were trying to model was far too complex for the predictive capacity we had available to us at the time. I've taken a few trips through the DOE website in the past year or so, it doesn't strike me that anything much has changed.
I am not adverse in any way to designers doing energy calculations, and am genuinely grateful for the MEC. I think they are all steps in the right direction. Further, I think it is instructive to do the calculations before we build anything, and compare our predictions to the result. We've got a lot to learn.
I'm no Luddite (at least not this way <G>) -- I spoke with an engineer at Sandia National Lab who built a house in the late 1980's, he has yet to heat it, and it has yet to vary more than 4 degrees F from a mean of 68 degrees in a 6,001 degree day climate. Impressive work to say the least, and a notable exception to my comment about predictive capacity. Given the number of variables we are dealing with, it is difficult for me to think that I could reliably work from the particulars of his experience to the generalities we face with every new site and every new floor plan.
I am also concerned that in the pursuit of efficiency we can risk losing sight of effectiveness; ultimately we have to live inside these engineering experiments, and in a perfect world, that would be a pleasant experience. Likewise, we need to be able to afford to build them.
Which brings me to Ron's question about experimenting with other people's money. Yes, it is a blessing. Now you also see why I am so conservative -- I have a pretty deep implicit obligation to be very careful. My preference so far is to start with what I know to be reliable under almost any circumstance, and make incremental changes based upon a combination of the best evidence available and the most sensible intuition about the particular challenge.
To go back to the Trombes, I didn't mind this experiment a bit. Sure, it required a lot of thought, but that's fun. If it didn't work, I could always remove the glass and the steel frame, fill the cavity with foam, stucco over it, and go think some more about what was to be learned. Not a real big risk involved, and a lot to be gained.
I try to work in increments that will be instructive, productive, and inexpensive. To paraphrase the late J.E. Gordon (in my opinion, one of the engineering giants of our time), Nature is the best designer of all, but she is difficult to copy, for she has plenty of time, and she eats her mistakes.
I certainly appreciate this discussion -- it is giving me the motivation to think through all of this yet again and renew my enthusiasm.
DRC
To go back to the Trombes, I didn't mind this experiment a bit. Sure, it required a lot of thought, but that's fun. If it didn't work, I could always remove the glass and the steel frame, fill the cavity with foam, stucco over it, and go think some more about what was to be learned. Not a real big risk involved, and a lot to be gained.
Not unlike my thoughts deciding to build a PAHS as my first, ever, house. I saw little risk. Worked out better than I'd hoped. Particularly, since I cheated substantially on Hait's design: more exposed wall, less earth cover. Penalty was 3º/yr in the annual swing. Huge percentage difference (43%), but easy to live with. Of course I'm ignoring climatic differences. Had an online engineer offer to do expensive mass calculations for me, but I see little need.
The next place, for us, will further experiment by adding an active solar system to the mix while mostly removing the passive solar. I can come up with a pretty good guess what the active solar will contribute, then the trick is to try to determine what the PAHS did. After living here a few years I have a good understanding what the passive solar does, and does not. That's where you get into diurnal/annual heat storage.
But without calculations I wouldn't have any idea how to size the active solar system. Remains to be seen if I did it right, but I sure hope that 600 gal, 5 ton tank for antifreeze is right. <G> It's in the building for the duration, used or not. And if a future owner wanted a conventional boiler, no problem with a retrofit.
It wouldn't be difficult to make a calculation of both solar gain and heat loss of your Trombe wall. Then, by comparing to your experience, you'd have a very good predictor. Might be you'd want a total southern Trombe, or not. And again, if it looked promising but didn't turn out that way, what's the worst that could happen? Pull it off and cover it over. And try to figure out why your predictor was in error.
I was very concerned with the client PAHS house getting standard financing but it turned out to be a breeze. The lack of comps weren't much of a hurdle and the appraisal sure tickled the owner and me. Nothing like starting out with 30% instant equity.
Nature is the best designer of all, but she is difficult to copy, for she has plenty of time, and she eats her mistakes
Love it!
I certainly appreciate this discussion -- it is giving me the motivation to think through all of this yet again and renew my enthusiasm.
That's why I tune in here. Not to mention what one learns from differing points of view. Thanks for the explanation. That Sandia engineer's house works almost as well as Hait's. Don't know what the engineer did, but I believe Hait's mass ideas are applicable pretty much anywhere. David pointed out how it could even function in Alaska. Downside? I don't see one.PAHS Designer/Builder- Bury it!
Cloud, You have hit the nail precisely on the head. In your words, "To the extent that the slab temperature rises through solar gain, it just means fewer btus you'll have to toss in there via other means. " This is the point. If you start adding heat from the sun when your slab temperature is already been raised by other heat sources you limit your potential to store the solar gains. Once your storage capacity has been reached further solar gains will result in higher indoor temperatures. As I said, heat storage is an essential condition for a house to meet his definition of a passive solar house. Nobody has said that a little solar gain isn't nice in any house in winter. It's a little bonus, but having a window on the south side doesn't make the house a good solar design.
Architect chap says that his houses can store four or five days of solar gain in the floor slab and that internal temperature swings are very small. He also says that there is no additional cost to building a passive solar design. I don't know whether he has ever done this with an ICF house. I think most of his work has been with wooden houses. Some are here: http://www.solarns.ca/
Dave your Trombe wall refinement sounds very good. Must be nice to have a client who is willing to put up his dollars for a test like this. Do you think it would be possible to do any serious measurement of its performance?
Ron
I'll choose to disagree with the conclusions, but won't press it beyond this post. We can leave it as reasonable people are allowed to disagree.
My take would be that if you're getting the kind of solar gain that would take a slab to saturation and beyond, except that the slab has already been loaded to near rejection of heat by the rfh, then you've been running the boiler too long or too hot.
And I especially wonder about the slab storing 4-5 days of heat. At what outside temps? That implies to me that if a dark cloud moved over the house and stayed there for 5 days solid with no additional solar gain, and the temp dropped to the design temp, that the house would still be near the same temperature as when you started. And that's with framed walls. I don't believe that--whether through the calculations or direct experience--or else have a different concept of storing 4-5 days of heat in the slab.
It comes down to btus for me. The house loses x many btus/h under certain conditions. If it doesn't replace these, the temp drops. And it can gain x many btus/h via the sun or heaters. I'd love to see the numbers to show a slab alone storing 4-5 days worth of btus at design temp without replacement.
And it doesn't jive with what I've seen here (not suggesting that mine is a good or bad system...just the one I'm currently observing). I have a 3200 sf slab, 8" thick, weighing about 350,000 lbs. On a typical winter's day, I have from 24-48 hours with no active gain through sun or rfh before the inside temp has dropped enough to bother us. That slab will theoretically provide 126000 btu with a 2 degree loss. I don't see any way for the numbers to support 4-5 days.
I'm not trying to be disagreeable, Ron. I'm still trying to understand all this stuff about gain and loss and the role of mass and the sun myself. But the numbers aren't adding up for me, and I'm a proponent of high-mass, passive solar systems. Think what a skeptic would say!!! :)
Cloud, I've been re-reading the material. I was wrong about that storage capacity. I can get back to you on that after I see him again. We do live in a temperate climate, though. The temperature seldom stays even as low as -5*F for very long.
Dave, your incremental and cautious approach to design is the same as mine and, I think, the same as most of the hands-on people I know in the construction business who take pride in the work. Very pleased to meet you.
By the way, have you gentlemen ever heard of this type of solar collector? http://www.solarwall.com
Initially, I was thinking about building a version of this unit to pre-heat the ventilation air but there seems to be little point as the building code here now requires a heat recovery ventilator, making returns from a solar air heater hardly worth the effort.
Ron
"Dave, your incremental and cautious approach to design is the same as mine and, I think, the same as most of the hands-on people I know in the construction business who take pride in the work. Very pleased to meet you."
Thanks, and likewise.
"By the way, have you gentlemen ever heard of this type of solar collector? http://www.solarwall.com"
Never heard of it.
You realize of course that now we're all waiting to hear what your architect has to say. <G>
DRC
I'm a solar engineer building a passive house with RFH. The Nova Scotia architect says you can't heat the slab with the sun if you've already heated it with fossil fuel. That's just not true. The sun will still add heat to the system even if it's already hot, say, 100 deg. or more.
Using more realistic numbers, on a typical cold night the high mass house might drop to 65. Fossil fuel is used to bring the house up to 70 by 7 am. Then the sun shines all day. That solar energy drives the house and slab temperature up to 75. Now you can see that the solar energy has been stored due to the increase in temperature of the thermal mass.
Here's a similar home using a geothermal heat pump. Check out the real-time instrumentation! http://www.ourcoolhouse.com/
>The sun will still add heat to the system even if it's already hot, say, 100 deg. or more.
We agree. And I've seen that real-time monitoring house. I woulda loved to do that, but I'm not that good with the electronics.
I have a ground source heat pump, too, along with high-mass (my house is about a million pounds), and rfh, and love the interaction of the components and the sun. Most comfortable and controllable place I've been in.
I agree, and I think this observation is essential to the design of homes that depend upon mass-compensated thermal performance. To design only for a worst-case scenario (the coldest week of the year) can distract a designer from recognizing the natural economy of modulating the diurnal temperature swing that, in most climates, is surprisingly accomodating to our needs.
A little solar home humor there. Probably too dry, sorry, couldn't resist. <G>
No reason to resist. <G> The next step is to plan not for diurnal, but annual. Takes a bit more mass. We're nearing the end of our heating season and our place is cruising along at 66°. Generally add a tiny amount of heat evenings unless it's been sunny. Then when all our neighbors are complaining about their ac elect. bills, we just smile. That's stored heat for next winter.
Add it all up and you get a home that is very resistant to thermal change. If it tends to be comfortable, it tends to stay that way all the time.
Exactly. Then when it turns out inexpensive to build, excellent.PAHS Designer/Builder- Bury it!
I'd like to hear more about the inexpensive part.
DRC
I'm guessing the inexpensive part is dirt. In lieu of siding, trim, paint, windows on 3 sides. Cheaper than concrete or water tanks. And as tough as, well, dirt.David Thomas Overlooking Cook Inlet in Kenai, Alaska
I sure hope so -- I just bought another machine, and I'd really like to build some houses with it. <G>
DRC
I'm guessing the inexpensive part is dirt. In lieu of siding, trim, paint, windows on 3 sides. Cheaper than concrete or water tanks.
LOL Dirt's the cheapest part all right. Actually, we have 3 largely exposed sides with lots of glass. That's why our performance suffers somewhat. We also don't bother with window covering on our 400 sq ft of glass. Costs us 1-2°, winter and summer, but with our mass it's affordable.
When I compared my concrete and steel construction costs with the builder I used to run a cabinet shop for, I was amazed. So was he. Dirt isn't the only cheap thing.
For instance, last house was 2k sq ft footprint, engineered for 300 tons overhead. Bar joists and decking came in at $8300 delivered, 40' span. Bear in mind that there is no roofing to buy, ever. Material for that house shell was right at $22k. Less labor than wood construction. And less skilled. Insulation is about the same as wood frame, but simpler to install. With the insulation umbrella, no water-proofing needed. 6 mil plastic does all the work.
I don't have the time this summer, but there's a recent arrival here who'd love one of these. Especially when he found out that the last house came in 2/3 the cost for a comparable house. Now he's looking at envelope houses as he can easily find somebody to build one. Not that I'm doing anything complicated, just difficult to find a willing contractor, as I found out when I started mine.
A correspondent often refers to my "dirt furnace", but it's also the ac. All with no moving parts or maintenance. Gotta have some excess heat sometime though (summer?), maybe difficult in Alaska. The original PAHS worked admirably in Missoula with 8125 degree-days, which has no month without a few.
Inexpensive. Works.
PAHS Designer/Builder- Bury it!
"To design only for a worst-case scenario (the coldest week of the year) can distract a designer"
I agree, but my first mission is to get people to design for that worst-case and no more. Quit over-specing the heck out of the furnace/boiler because you can't/won't figure out the heat losses.David Thomas Overlooking Cook Inlet in Kenai, Alaska
I agree 100% -- those are some finely drawn but important distinctions, and the success of a solar/high-mass home depend upon them. I hope you'll say more about this.
DRC
I think you are talking about the desirability of approaching a no-heating system house. And of course 5 billion out of 6 billion people on the planet live that way right now. And the majority of our anscentors.
They found the right cave (southern exposure, rising passage as a heat trap) or built it from abode or stone.
Or ice! The Iniut in their temporary hunting dwellings (igloos) and in their permenant earth-sheltered dwellings didn't have RFH, boilers, heat pumps, HRV, etc. Tight, high-mass, airlock by virtue of a cold-air trap. Manually adjusted openings for air flow. Body heat was enough to keep it warm. At -50F!
Alas, in a code-enforcement area, you'll need an automatic whole-house heating system. And that is probably a good idea for vacations, etc.
Barring codes, I see no problem with designing for something less than worst case (if the owner/occupants/buyers are on board). When it does get cold - put on a sweater! Like the rest of the world. Or plug in a few electric heaters. Or bake a batch of cookies.
I know a bunch of people up here who live in log cabins. And one guy who lives in a treehouse (year round!). If they can make it work at -40F (with wood heat), why does anyone have to have forced hot air when they've got hours more sun in the winter with less extreme cold to deal with?David Thomas Overlooking Cook Inlet in Kenai, Alaska
David, that's exactly what I'm talking about. The fact that the rest of the world has been making it work for at least 300 years is encouraging to me, too.
One of the reasons I spend so much time reading Breaktime is guys like you. It's a real blessing to be able to have these discussions, not only to hear new ideas, but to also reconsider ideas that I thought I was familiar with from a different perspective (like Alaska.) <G>
DRC
"The fact that the rest of the world has been making it work for at least 300 years is encouraging to me, too."
Yes, "at least" I found it striking to wander around Chaco Canyon, occupied 850 A.D. to 1250 A.D.:
http://www.nps.gov/chcu/
The original construction anticipated (with adequate wall thickness) the third and fourth stories (that were constructed centuries later). Or maybe they were just behind schedule and over budget like everyone!
AND the concept of solar rights was in place. Each dwelling unit saw their slice of the sky, unshaded by the neighbors. 1000 years later and what, maybe only Berkeley and Madison have adopted similar concepts?
"different perspective like Alaska"
Solar only is tough up here. You could have two weeks of clouds and 5F. At least the -40F is always due to clear weather, but with 5.5 hours sunrise to sunset and a max (max!) sun angle of 9 degrees on Dec 21, the payback wouldn't be there.
What is very doable, even up here, is to need no heat in the spring and fall. I designed my own place around views and the water and volcanos are to the west. The only neighbors are to the south, alas. But with a tight house and the glazing turned 90 degrees wrong way round, I still need no heat above 40F in any weather. 15-20F if sunny. http://www.alaska.net/~dthomas/ournewhouse.html
I'd love to do a earth-massed house up here. 21 hours of daylight in the summer would allow quite a bit of soil and water heating. And land is SO cheap, a few acres costs less than a big water tank.
Pump GW, air pre-heat, solar boost, reinject up-gradient in the summer. Let it flow to your heat pump well in time for the winter. Work off of 70-85F water instead of 40-50F.David Thomas Overlooking Cook Inlet in Kenai, Alaska
Dave, very nice looking house, just about what I pictured from your posts. How close were we when we drove from Anchorage to Homer? PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
"How close were we when we drove from Anchorage to Homer?"
Paul, thank you. As you passed through Soldotna (those strip malls along the highway), you were 10 miles inland from Kenai. We have, over 120 degrees, the kind of views Homer has for 270 degrees.
Homer's marine influence earns it the title of the "banana belt" up here.David Thomas Overlooking Cook Inlet in Kenai, Alaska
Alas, in a code-enforcement area, you'll need an automatic whole-house heating system. And that is probably a good idea for vacations, etc.
Nope. The building dept. asked if I minded putting in a couple of baseboard electric units. I installed a total of 10' to make them happy, not required. Since have been removed. They no longer make the request. First experience was the most difficult for them.
When the house never even gets down to 60°, it's ideal for vacant times. Only for HO's insurance did I run into difficulty. Several companies turned me down for lack of a heating system. Their fear? Frozen pipes. I asked one if they could write an exclusion. Didn't get anywhere. Fortunately a number of companies were better informed.
If we would settle for 65-66°, wearing a sweater or whatever, we'd have a house that "needed" no heat. As it turns out a couple hrs of a small woodstove will get us up to 70° in the evening. That's for 20k cu ft. PAHS Designer/Builder- Bury it!
Hello
I am a buderos with wirsbo or tekmar controls.I would not use electricity unless there was a compelling reason.Oil at this time produces the most therms as compared to gas with a reduced cost of operating. For DHW I would use a indirect and run it off the boile.I would not use pumps but rather a belimo motorized mixing valve.This is important stuff being and the system will be expected to operate for years.For really good help on line try heatinghelp.com.There forum is called the wall.
Hope that helps
Rod
Rod, I see this is only your second post. Welcome. But I don't have a clue what you're talking about.
My point was that for anyone who is currently using electricity for ac/dehumidification, a heat pump makes great sense. Whatever you're talking about apparently won't do the same thing at all.
?????PAHS Designer/Builder- Bury it!
VaTom, Here's my interpretation of Rod's post with edits of typos and (clarifications). Despite his brevity, he makes good recommendations on specific components. His apporach is more traditional than mine, but there is some solid logic and experience behind that. -David
Translation: I am a (fan of) Buderos (brand oil-fired heating systems) with Wirsbo or Tekmar controls. I would not use electricity unless there was a compelling reason. Oil at this time produces the most therms as compared to natural gas with a reduced cost of operating. For DHW I would use a indirect (hot water heater which utilizes a heat exchanger) and run it off the boiler. I would not use pumps but rather a Belimo (brand) motorized mixing valve (info at http://www.belimo.com/belimoshop/index.html ). This is important stuff being as the system will be expected to operate for years. For really good help on line try heatinghelp.com. Their forum is called the wall. -Rod
Thank you. I guess Rod's response wasn't really directed at what I posted, but the thread in general. And if you're gonna have a boiler working it seems reasonable. I'll be using a liquid/liquid heat exchanger with my solar system to allow use of antifreeze. Which seems like a much better system yet, for those of us who get reasonable insolation.
As an aside, I ordered rebar this am. Quotes are only good for 1 day. My cost is up 60% over the last two years, mostly since December apparently. I believe BH mentioned steel price variablility recently. Last night I got an email from the left coast saying his rebar costs were up 600% (yes 600, no typo). Tomorrow they're bringing out enough to finish my house. Doesn't yet drastically affect my overall costs, but something to be aware of.PAHS Designer/Builder- Bury it!
Check into basalt rebar perhaps. Before the steel increase, it was about double steel. But now, it should be looking a lot better.
That real-time monitoring is very impressive.
As for slab storage I bow to the weight of expert opinion,but surely you'll agree that you can't store as much heat in the slab if it has already been heated.
Ron
I wouldn't frame the issue from that direction. I'd frame it this way:
Goal: heat the house via heated floor rather than via forced/heated air
Method: Create a design that heats the floor as much as possible via solar gain. Use supplemental heating only as necessary to make up for what the solar doesn't provide.
Rather than seeing a slab filled with heat via the boiler able to absorb limited additional via solar, see it as a slab filled with heat via solar to maximum potential, with the boiler making up the gap, just as baseboard or fireplace would have to in lieu of rfh. Just a different perspective, where rfh is viewed as supplemental only.
The slab CAN store very nearly the same amount of heat even after it's been heated. The key to understanding this is to let the slab "overheat" somewhat. If you can't stand a room temp. a few degrees above your setpoint, then yes, you might close the shades and then you are rejecting the heat. High mass houses just don't have this problem.
Energy stored= K * Mass * (T2-T1)
Check into basalt rebar perhaps.
Had to Google that one. Composite, I've run into. I'm all set, but I'll ask about availability. Looking to be shocked if any of my suppliers has any idea what I'm asking for. Also gotta see the specs. Don't want to kill anybody, especially me.
Thanks.PAHS Designer/Builder- Bury it!
---"...opening a door to let the dam dog out ..."---
Do get a screen door for the back porch/mud room and install a dog door on it.
No more letting the dog (or cat) in -out-in-out-in-out........<G>
> > ---"...opening a door to let the dam dog out ..."---
> Do get a screen door for the back porch/mud room and install a dog door on it.
I've got a magnetic sealing dog door in the mud room / arctic airlock space (6' x 8') with two exterior people doors, one outside, one inside.
So the inside door can be left open for a free-range dog. Or closed if there are moose or meter readers around. And the house is pretty tight either way.
David Thomas Overlooking Cook Inlet in Kenai, Alaska