Big picture HVAC ideas for 4-story house
Hi, all!
I’m in the design phase for a house for myself outside of Asheville, NC and am trying to figure out which direction to take the HVAC in. Our area has temperate weather…average high in the upper 80’s in August, average lows in January in the 20’s, though it does get windy.
Since it’s so temperate, we’re going to aim to save on energy by opening the windows and using techniques from older homes…10′ ceilings, ceiling fans, operable transom windows on the bedrooms and baths, probably a whole-house fan, some passive techniques too, aimed at keeping cooler in the summer.
The home’s design is typical, it’s a 42 x 42′ square with a few bumps here and there to add detail. When you put that on a basement and finish the attic, though, it explodes out to almost 7,000sqft. I’ve got a pile of kids and a close family so we’ll put it all to good use.
The other details that might matter…the walls are mostly brick, some hardie plank, not sure if I’ll go 4″ or 6″ with them yet. The finished attic doesn’t (as it is now) leave enough unfinished space for an air handler. There’s a central stairwell that stacks over itself from the top to the bottom. I can close a door to close off the basement and the attic. Next to the stairwells I’ve left accesible utiility areas in a stack from the attic to the basement where there’s plenty of space…straight runs available through that area. I’m going to truss the floors so there’s space there as well. I don’t plan to build tight enough to warrant an air exchanger, not that you ever need one if you have kids that play outside.
What do you guys think is the best, big picture, plan of attack for a big & tall house, in a temperate climate?
Thanks for your help!
Steve
Replies
no matter the size, the most bang for your buck is going to be to build tight. you dont need to be ultra tight in NC but even a flash and batt with closed cell to limit air movement is worth consideration.
if you can budget for ground source heat, that should be on your list. hydronic heating would be another option that if in your budget would be very comfortable in NC.
If the above is out of the question, look into zoned mini split systems. Specially with limited space for mechanicals, you can have duct or no duct splits that run very efficiently. For a relativly small increase in cost you can have them powered by solar panels wich will for the most part zero your usage on energy.
Mark,
Your response opens up a whole pile of discussions I wanted to have...for now I'll shelve solar power and figuring out which tight-building techniques make sense for moderate climates. Let's just assume that I won't need to run the air exchanger required of a really tight build.
I actually DO have lots of space for mechanicals. That's what makes the decision trickier.
I like the idea of the mini-splits, but wonder if they can beat an optimally installed, modern, heat pump (and a real fireplace for the nights that would kick on the electric coils). I'll be able to use metal ducting and straight runs. With trussed floors I should be able to get the registers and returns in just-the-right spots...
Do you think mini-splits would ever be able to make up the difference? Even if they save in electricity, they add so many more moving parts to keep serviced over time. In a battle between efficient systems, one service call could take years to recoup!
I'll look into geo-thermal. It probably makes sense, especially if there's tax credits.
I would love to hear your (or anyone's) thoughts on beating the ideal-install of the heat pump...maybe even a heat pump using geo-thermal...
Thanks!
Steve
currently you can use the federal tax credit avaliable for ground source heat pumps (if the specific brand qualifies) of 30% material/labor.
if you have the space to trench your system you will save a considerable amount of $ in the loop installation. if limited space, then you would either need to have wells drilled and the lines installed in those (without specifics i would say 3-4 ). If you have a pond or water on your property, this is the optimal way to install.
Mini splits should not have any problem out preforming any modern heat pump. the only way i would see maintenance being a problem is if you are out of service area for anyone that is familiar with them. what part of NC?
If you encapsulate your new home with closed cell it will be a very good idea to consider (or at least know you may require one ) a heat exchanger. These are not a big deal and shouldnt deter you from chosing this option. I have encapsulated our home, and with the amount of time my kids leave the door open while playing negates the need for one (although we have it) I have 2.5-3" on exterior walls, 1.5-2" on the bottom side of the first floor and 6" in the attic.
If you opt for flash/batt , i would suggest framing with 2x6 exterio walls. you can have the insulation guy spray a very thin layer (only need complete coverage of all exterior walls, attic, bottom of first floor subfloor and then insulate with conventional methods (fiberglass or the like)
the above and your windows/doors are the items you should sacrifice other wants for to be able to install the top of the line your budget can handel.
With that large a house you definitely need a multi-zone system, at least one zone per floor. But a zoned system is possible with pretty much any technology, from conventional forced air to hydronic to various hybrid systems.
And, while some folks south of here seem to have the impression that an air handler must be in the attic, such is not the case. An air handler can be pretty much anywhere, and there can be several, depending on the requirements. (It helps if a single air handler is centrally located, but in a 4-story house that wouldn't be in the attic. The attic is often used in smaller homes simply because it's "unused" space, but it's false economy to limit your design to only consider an attic location.)
Similarly, zone control valves/dampers need not all be on one location -- they must be "accessible" wherever they are, but beyond that there is considerable flexibility.
My thougths:
I had figured, if I go heat pump, that I'd use one of the new air handlers that can handle multiple zones. I need to look a little closer to see if I can get one to handle my 4 zones, or if I'd need two. With the "utility shaft" I've got drawn up in the house it'd be easy to set the dampers and what not required for one of those. The design will also allow the entire system to be inside of conditioned space.
I like the mini-splits, but it seems like I'd need so many of them that the cost of install and upkeep wouldn't make sense. For the open parts of the floor plans you can make it work, but for all of the different bedrooms and bathrooms that'll alternatively open and close doors? The south facing bedrooms versus north. So, probably 7, multi-zone mini-splits...at, let's say $3,000 a piece...$21,000 is going to be pretty close to the cost of the geo-thermal install of the heat pump. Imagine all the thermostat battles you could have raging in the house at any given time with 14+ zones!
I.r. the geo-thermal...I'm on some acerage. There's a pond I share with a neighbor, but that's about 500' away from the house and about 150' downhill. I'd imagine I couldn't get that far.
I'm out in the boonies and the quiet is really nice...I hadn't previously thought of the geo-thermal on the heat pump dodging the need for the outdoor compressor. I kinda like that. With the air handlers in the basement the whole system would be really quiet.
Still need to spend some time considering the insulation...I know there's some good sources out there to help and I'll look them up when I get a moment. I'd really like to save by not having the heat exchanger. Between the double hung windows, fireplace, kids, stovetop and bathroom vents and the size of the house I think I'll be okay. But I'll do my due diligence to make sure.
I agree about servicing the simple units yourself. It's not "rocket surgery" after all. Sometimes, though, there's only so many hours in a day and it's worth it to call a pro.
The Questions!:
Can I run geo-thermal down to the pond (500' away and 150' downhill)? I'm about to have the regular well drilled. Wonder if I can get a "multi-hole discount" if the pond's no good!
Anybody ever use a pool for the geothermal? This could be just the justification I need!
Am I crazy to think I could need 7 mini-splits? It is 4-stories, 6 bdrm, 4.5 bath, afterall. Sounds really ostentatious when I put it that way; the house is actually pretty modest aside from the size.
you would only need 4 mini splits. one per floor. you can get multiple zones out of each one. there wouldnt be a thermostat battle. these things are crazy efficient and are very capable of handeling zones.
if the pond is accessible, (by that i mean if you can get a trench to the pond at an average of 4' the deeper the better) and your neighbor doesnt have an issue with the loops in the water that will be your least expensive option for loop installation. pool thing is no a good idea.
well drills are VERY efffective, take up virtually no space and make for an easy install, price tag is higher and the loop needs to be installed by a certified installer (at least in these parts) because it needs to be grouted with bentonite (choice grout around here).
Thanks for the help!
Thanks for the help guys. I'll run the plans by some HVAC guys locally for some quotes and see how it all stacks up. I'll also run some of those estimators you guys recommend to see what I can learn from them. I appreciate you guys taking your time to help me out!
-Steve
'one service call'
from that, assume you think hvac is way beyond your skill set or 'intellignece' capability?
I'll second the mini-splits. Even someone who does not think they have the skill sets can deal with mini-splits, both install and any future servicing.
7000 sq ft - Maybe up to 4 or 5 24,000 BTU units, strategically placed. You can find them online for under $1500 each for 18 SEER. The outdoor part is very quiet, for folks used to an old 'window shaker' AC or even a 10 YO heat pump, they basically are 40 dB quieter, cannot hear inside the house.
You can do all kinds of trades. *See below for own house.
Do a search for energy code compliance, you may have a NC specific one, ours in WA has a WSU energy code complieance spreadsheet, you can find it with a .WSU energy code' search. Somehow the link would not paste here.
Do that spreadsheet (or the NC psecific one if available) to see how many mini-splits you need.
My first mini-split, put a 2T mini into addition on son's house, easy DIY install (just buy a vacuum pump and use POE oil on the flare fittings). It has worked flawlessly for 3 years, Seattle area (almost never gets under 20F, once in 40 years), and no aux heat needed. Do note that a 24,000 BTU unit may only produce 15,000 btu/hr at 20F, so size accordingly.
*Own house is 5300 sq ft, built before mini-spits so dont have any except one on the barn shop. House has a 5T ground source (DIY from scrap parts for under $1K) that kicks in when air temp outside drops below 43F. Above 43F outside, air-air heat pump of only 2T but custom built on 7T condensor and evaporator, so > 5 COP. (5X the heat out as electricity put in) If you went custom like that, I'd guess an contractor would want something on the order of $20K or more, and to DIY you need your won backhoe, etc and a few more tools. However, 5 mini-splits at $7500 total DIY install (2 weekends) and you have made yourself big bucks per hour for those 2 weekends. Order on-line and save >$500 sales tax also!
Of course, there are others here would tell you you need to hire a REGISTERED professional licensed engineer and a green certified installer to do any of the above, and tell you asking us bozos on the web for 'how to' is na exercise in futility - that assumes the average HO is pretty dumb.
If you really want to learn, search "mollier diagram' and 'vapor cycle compression' and enthalpy; then look at supplier data and do your own comparisons.
Do you also buy 2 of the same toaster (same computer, same car or truck, etc. etc.) and let them sit in storage until you need them? What a waste of old technology, not to mention money.
Big Picture?
The principle is the same for any dwelling if you're interested in maximizing energy effeciency: take advantage of any free energy provided by mother nature and minimize paying for fossil fuel energy provided by utility companies.
YOu do this buy taking advantage of any active or passive solar and wind building techniques within your scope of knowledge and budget while minimizing the loss of energy you must pay for to condition your home. That's the big picture. The little picture is too broad to cover in this forum and you will never be able to provide all the details of your project that should factor into your decision making. There are many good books and articles written on the subject by folks such as Joe Lstiburek and Peter Yost. My advice is to sign up for Green Building Advisor (yes, you usually have to pay to play) and go from there.if you plan to take a D.I.Y approach. Realize that you will probalby fall well short based on your short learing curve opportunity. Otherwise interview a number of professional HVAC contractors that can help you with your goals. You may want to hire a third party energy consulting firm prior to engaging your mechanical contractor. If you find a trustworhty source that can do both, then consider yourself lucky.
Least of all would I rely on any detailed advice for your project volunteered from the bozos on this free forum because most of them have no idea what they're talking about.
another perfect example
of you having nothing to contribute yet not being able to help your self from being an as s wipe...
Wall acne.
Every time I see a mini-split, the air handler is a hideous 'wall acne' zit. Can you get a handler that hides in a closet and the ouput is just a vent?
I agree with the comments to build a super tight, super insulated house.
I too would look into using geo-thermal HVAC.
Good luck.
A couple of mini-split ducted air handlers.
http://www.lg-dfs.com/low-static-ducted-multi-f.aspx
http://www.fujitsugeneral.com/duct.htm
mini split air handlers
Interesting, where do these get mounted? In the wall, under the floor or a closet?
Thanks.
These ducted units need to be horizontal for drainage, so they usually go up at ceiling level.
Closets are an easy location, as the top foot or so the the closet is rarely used.
Could also run some soffits in the rooms for lighting / deocrating purposes, and put them in that. Attached picture shows a decorative soffit in a bedroom that could also house the air handler. Picture is from the Family Handyman article.
There are others intended for wall mounting: http://www.lg-dfs.com/art-cool-gallery.aspx
Also, ceiling mounted cassettes: http://www.fujitsugeneral.com/comp_cassette.htm
Other manufacturers have similar products.
Wall acne!
That cracked me up!
I think we're going to go with the heat pump and geothermal. In the end, the idea of not having fans outside to make noise and, for that matter, any mechanical equipment exposed to the elements to rust, oxidize, have parts stolen, or be infested in critters of any kind, etc, swung the decision.
Though we maybe have been able to save some energy usage with the mini-splits, I think the temperate climate and our plans to offset much of the cooling load with a whole-house fan will reduce the advantage. We see the extra cost of the geothermal on the heat-pump as a splurge. Hopefully, in the long run, the pay-back math works out, but you never know.
I had a chance to talk to an HVAC company that installs a lot of the geothermal systems around Western NC. He says we'll need two units for the house to move the volume of air we've got, even if we build tightly.
To save a buck, I think we'll set one of the pumps to run the basement and the attic and one to run the 1st and 2nd floors. Since the attic will have the most need for A/C in the summer while the basement needs almost none, and neither will need much help with heating in the winter, it made sense to give that job to one pump and have the other run the two middle floors.
Hopefully, since neither will be pushed too hard we'll be able to reduce the size of the units. That setup will also allow us to turn off the basement/attic pump altogether when we don't need any conditioning on those floors, say after the kids move out.
Anyone think we're making a bad choice?
Steve
somewhat
Steve_Hoff wrote:
That setup will also allow us to turn off the basement/attic pump altogether when we don't need any conditioning on those floors, say after the kids move out.
You know, they make things called thermostats that do this automatically.
On the other hand, if you're thinking each floor (or 2 floors as the case may be) will be its own conditioning zone that can be turned off w/o affecting the other(s), then theoretically you should be insulationg each zone with its own seperate thermal envelope. That usually means insulationg between floors w/ a means for limiting air circulation between each.
Finally, in my opinion, any cost effective climate conditioning delivery system should be situated within the building envelope. By placing one unit in the attic it seems you are creating inefficiencies with a need for additional conditioned space (in attic) when you've indicated you have the space within your dwellling proper.
?
deadnuts wrote:
Finally, in my opinion, any cost effective climate conditioning delivery system should be situated within the building envelope. By placing one unit in the attic it seems you are creating inefficiencies with a need for additional conditioned space (in attic) when you've indicated you have the space within your dwellling proper.
when houses are proposed for geothermal, they go hand and hand with a complete envelop package. this means in most cases, that the house is sprayed with closed cell and the attic becomes part of this conditioned space. if this hvac contractor is as experienced as he is stated to be, he will more than likely even spray the duct work as well. once again the value in you personal oponion.
horse hockey
mark122 wrote:
deadnuts wrote:
Finally, in my opinion, any cost effective climate conditioning delivery system should be situated within the building envelope. By placing one unit in the attic it seems you are creating inefficiencies with a need for additional conditioned space (in attic) when you've indicated you have the space within your dwellling proper.
when houses are proposed for geothermal, they go hand and hand with a complete envelop package. this means in most cases, that the house is sprayed with closed cell and the attic becomes part of this conditioned space.
No; it doesn't. Pure speculation on your part which is par for your course.
speculation?
please. you clearly have no experience with ground source systems.
ill repeat myself cause simple minded people like you always need to hear things more than once. if someone is concerned with chosing paint colors, removing wall paper or has a question on using over priced tools then you should confidently chime in and know we are all ears, otherwise, know when to STFU.
Both units in the basement...
The house plans we've got now have both units in a utility room in the basement. We've designed a "utility shaft" through all the floors of the house to allow the ducting, chimney pipe, and the major plumbing to all have a straight vertical shot. I'll use the trussed floors to fit the rest of the ducting.
We're planning to spray and I'm considering putting a reasonable layer below the finished attic. I guess that depends on the price since the finished attic itself will be well insulated.
I get the concept of a thermostat. If I turn off both of the zones assigned to one of my pumps, then it'll never turn on, and the other will be utilzed at a reasonable rate. That should save some money...the best sized pump can't quite keep up on the worst day, right?
yep, ya betchum DN..
always buy more than one of anything just for the spare parts... of course, you should know I ONLY buy used stuff, less than 10 cents on the original dollar, surplus, garage sales, etc.
never ever have hired a professional engineer either <G>
Daily driver is an '84 S-10, get near 30 mpg as modified. Previous ride was '71 datsun (stillhave for sentiment) but sold the other 5 Datsun truck I had. The PU got 42 mpg as modified and the way I drive - manual etc for everything or small elec vac pump for brakes, hilly here, so engine off every time I go downhill.
Did I say I have 6 S-10s, 84 to 91. 3 for spare parts, 3 driven.
I have not yet found a spare 1995 land rover, cannot find another one for $200, must have cleaned out the low end market with that one two hundred dollar special...
BTW, I do not own a SINGLE festool.
not surprised
junkhound wrote:
BTW, I do not own a SINGLE festool.
This doesn't surprise me one bit.