We have 1985 electric baseboard heat in a passive solar home. We are looking to change to something more efficient/cheaper. The entire house is finished, so adding pipes or ducts would mean ripping up sheetrock. Does anyone have experience with the Hydro-sil products, or the cove mounted radiant units. Are they any more efficient than the old electric baseboards. Thanks for any information.
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Yes they are a lot more efficient, but first what climate are you located in? Is this a one story or multi story home? Do you have a basement or crawl space?
Hi - Thanks for answering. The house is in Connecticut. It has no basement/crawlspace. It is a passive solar built somewhat into a hill. The front is all glass and there is only a small unfinished attic space. Everything else is completely finished with sheetrock/tile/carpeting. What kind of experience do you have with other kinds of electric heat? We've been supplimenting with wood (free on our 13 acres), but we are tired of the work. Any suggestions/facts would be appreciated. Thanks, Joy.
How do you figure that they are more EFFICIENT?
They are still resistive heat and give out 3.4 BTU/hr for every watt.
You are not fooling mother nature just by putting the heating element in an oil bath.
Bill,
I stand corrected, because of the way I worded my reply. Electric resistive baseboard heat is totally inefficient, and only in comparison to it are oil filled radiators better. They work on a little better portion of the inefficient curve, but are still very inefficient.
I asked some questions intending to get right back with the following suggestions based on Joy's reply.
Get a heating contractor in for some options. Duct work can be run in the attic with ceiling registers. Pipe can be run around the perimeter for hot water baseboards. Don't be afraid to cut into the sheetrock. It's the easiest part of the house to redo. Heat pumps are the only efficient electric heat, but not in Connecticut. Small gas room heaters have come a long way in recent years. If natural gas is available it may be an option.
" Electric resistive baseboard heat is totally inefficient, and only in comparison to it are oil filled radiators better. They work on a little better portion of the inefficient curve, but are still very inefficient."
I am still not sure what you are getting at.
Efficency is the ratio of energy out to energy in.
In the case of resistance electric heat of any type that is almost 100%. The only losses are resistive losses in the wiring that is outside of conditioned space.
There is no "curve" on resistive highing devices.
Bill,
I am going to start with a disclaimer. I am not qualified to give a detailed explanation of the theory, but I won't let that stop me.
Tungsten is by nature a variable resistor. It has almost no resistance when cold. Let's say 0.1 ohms, but when white hot it has a high resistance, let's say 100 ohms. This is where the first part of the curve comes in. Immersed in oil the element is kept in the cool low resistance area, because it transfers its heat to oil much more readily then transferring it to air. The second part of the curve comes from the mass of the oil filled heater. It stores a large quantity of heat at a lower temperature and releases it over an extended period producing a steady flow of warm not hot air. It gives off less infra red light which is spent energy. It basically just produces more useable BTU's.
It is still very inefficient, but more efficient then a toaster element.
"It is still very inefficient, but more efficient then a toaster element. "
A toaster element might be very efficient, but it depends on what you are trying to do.
But a toaster using that element is probably not very efficient. In that case the purpose is to "char" the toast. I don't know now much energy that process takes, but a lot of heat energy is lost. Just feel the case. But it is proably more efficient than say a gas or wood fuel based toaster would be. (And yes they used to make them, still might find them in Real Goods are similar catalogs).
But where are not trying to make toast, we are trying to keep a house warm.
First of all tungsten is not normally used as a heating elemenet, you don't want it to be glowing white hot, you want to be making heat enegery, not light energy.
Nichrome is one alloy that is used. And most metal alloys due have negative temp coffience resistance. But that does not make any difference.
If it is 10 ohms is will draw 12 amps or 1440 watts. Run it for one hour and it will cost you the going rate for 1.44 kwh of electricy and supply 4915 Btu's of heat energy.
If it is 20 ohm then it will draw 6 amps or 720 watts. For one hour you pay for the cost .720 kwh and get 2447 Btu's of heat energy.
There is no curve. No matter how much electrical energy that you put into the heating element you get the proportional amount of heat enegery out. Is is 100% efficient.
John,
I was in complete agreement with up thru "I am not qualified...".
The rest is nonsense. You an HVAC contractor?
Lesson Learned
I should have only made one statement on my last post. "I am not qualified"
John,
Sorry for being so blunt. We have had overly invloved disussions in this forum recently on electric heating and efficiency.
Oh, the electrical efficiency question again. My question is, if we agree that energy in equals energy out, then: Of the energy going in to your baseboard heaters, in what form is the energy coming out? As stated above, if your element is glowing red, look out, so it isn't light. Same goes for sound; if your baseboard is making noise, you've got problems. Same for motion; baseboards shouldn't be moving. I'm pretty sure you aren't converting energy to mass. So, really, with a baseboard heater, all of the energy in goes to heat. For all practical purposes. Incandescent light bulbs are an example where you get heat and light, so they aren't very efficient from a light producing point of view.
I always thought about this when people in cold climates talked about insulating their hot water heaters. My response is, if you heat your house 9 months of theyear, and the water heater is in the heated part of the house, what's the big deal? Any lost heat goes into the house anyway, right? Of course, this is from a guy who, when I was at college, would leave the bathtub full of hot water until it cooled off, figuring it was a shame to throw that heat down the drain.
"Of the energy going in to your baseboard heaters, in what form is the energy coming out?"
The simple answer is thermal energy. More precisely, the air, that by natural convection, passes over the heat transfer surface, experiences an increase in temperature. At a molecular level the increased energy is an increased molecule velocity. Some of the energy is radiant, though not that much. (The term "radiant floor heating" is inaccurate, btw, they are very effective convectors, but since the absolute temperature difference is slight, the energy radiated from a 100 degree floor is also slight, compared to the convection transfer) Some of the energy is lost to entropy.
"Incandescent light bulbs are an example where you get heat and light, so they aren't very efficient from a light producing point of view."
Absolutely, which is why the poorer quality (my opinion) of flourecent lights is acceptable because they are much more efficient at producing lumens from an electrical current.
"...if you heat your house 9 months of theyear, and the water heater is in the heated part of the house, what's the big deal? Any lost heat goes into the house anyway, right?"
No, domestic water heaters, are with few exceptions, relatively inefficient, (electric dwh's excepted) as compared to say a condensing furnace. So a fair portion of the enegry consumed (~20%) goes out the flue/vent. Add to that the fact that you are heating water to 180 degF and the potential to transfer heat to the surroundings is relatively high. Typically a dwh is not in a fully conditioned space, like the garage or the basement. On the other hand, inefficiencies ignored and assuming it is located in a heated space, then you're right. My water heatr with a tank is insulated. My tankless is not.
I suppose that my grasp of the proper physics terminology is lacking somewhat. Look at it this way: would you get the same mileage in your car if you were constantly speeding up/slowing down, as you would cruising at a steady speed? Same principle applies with heat. It's more efficient to maintain a steady temperature, than it is to cycle; the more extreme the cycling, the less efficient it is.
As for the "red hot wires:" there are heaters out there that "radiate" by heating a wire to red-hot (just like a toaster). While today these are most often portable space heaters, this design was common in the '60's in a baseboard heater. The elements were usually out of direct sight, and had a fan blow air over the element. These, oddly enough, are also called "radiant electric heaters."
Light exists in an entire range that we cannot see. Every material is transparent to some part of this range. For example, X-rays are a form of light. A heater can be more "efficient" when it produces more of its' "radiation" in those wavelengths that are absorbed by air. This is why an oil or glycol bath is an effective way to increase the "output" of a heater
"It's more efficient to maintain a steady temperature, than it is to cycle; the more extreme the cycling, the less efficient it is."
The anaolgy of the car and milage doesn't apply and this statement is wrong. It is not more efficient to heat at a constant rate tham at a variable rate.
"A heater can be more "efficient" when it produces more of its' "radiation" in those wavelengths that are absorbed by air. This is why an oil or glycol bath is an effective way to increase the "output" of a heater"
This too, is wrong. It is marketing bunk designed to sell a product to people who don't know any better. They do a good job of dispersing this nonsense and you and many other obviously are taken in by it. The efficiency of a device that's sole purpose is to convert one form of energy or another into sensible heat is simple. (Heat pumps are not in this category) Heat out/energy in (in the same units) is the efficiency. Whether that heat passes through cast iron, copper tubes with aluminum fins or a mass of oil, is inconsequential to the efficiency of the device.
Love this type thread, helps to understand the 'misunderstandings' of basic physics/engineering that many people have. Listen to Bill on this one.
BTW: did you know that if you put a cup of HOT water and a cup of cold water in the freezer, the cup with the HOT water will be frozen FIRST. Understanding this type seemingly 'wrong' result is a first step in understanding T^4, heating, cooling, entropy, enthalpy, perpetual motion, and similar questions.
My freezer will not freeze hot water faster than cold, that's baloney. How do you explain this idea? I suppose I could give you the empirical results of my experiment in hot vs cold water freezing.
The majority of energy transfer to freeze water is in the heat of fusion. When the hot water is put into the freezer, some of it evaporates, so that the actual amount of water frozen is thus less for the hot water. Run the math.
Not only that, but especially if you run fresh tap water, the cold water has more air in it, which makes it take longer to freeze.
It's on the order of 80:1 (heat of fusion to specific heat), if memory serves, isn't it?
Be seeing you...
Edited 12/4/2002 4:05:34 PM ET by TDKPE
Hey everyone..............................
Let's add to this discussion ...."molal freezing point depression constants" which may be the real basis for the difference in freezing time between hot and cold water placed in the freezer.
Or maybe................................ "endothermic molecular motion"?
But what about message # 1 of this thread.............and the needs of this forum participant (JOY) to have a functional answer to the problem?
Debates of symantical terminology give no solutions...only more "hair splittin".....
Let us address the needs to be filled by the original question.
Back to basics........Iron Helix
Edited 12/4/2002 9:06:31 PM ET by Iron Helix
OK IH, back to original, simple answer is no, bite the bullet and add pipes or ducts.
Heat pump if moderate climate (not much below freezing), geothermal HP otherwise, CH4 3rd, other options tbd.
Saw a program on the tube regarding that. The question was raised from people making Ice cream and putting hot mixings in the freezer at the same time as room temperature mixings.
The described result was that the hot mixture kept rotating in the vessel, that is the hot liquid rose to the top and the cold went to the bottom until it froze. The density of the material causes the turbulence. The changing surface was what better exhausted the heat from the liquid as the only surface that transfered heat to the freezer was the exterior skin of the icecream mixture.
True there is a calorie of energy for each degree per cm2, and the warm mixture had more energy to deposit in the freezer compartment, but the fact that the thermal transfer was quicker due to the greater differential at the surface as well as the surface continually mixing made the warmer mixture freeze faster.
Good point Booch.
1st order effects (e.g HOF) often are either aided or hindered by 2nd, 3rd,...nth effects. Good corollary on why the weather forecasters often get it wrong, many effects.
OK, some investigation has revealed that only under certain conditions, hot water may freeze faster than cold. Very interesting.
My respects, very few posters here acknowledge having learned something unless of a specific question asked.
That was one of the most preposterous sounding theories, but it does make sense after a bit of studying. The water has to be highly insulated from contact with the freezer so that it stays warm longer so the hot water looses mass from evaporation while the cold does not, the cold water has less entrained air to start forming ice crystals and fewer convection currents. Probably not much difference in the time to freeze though.
There are several web sites that discuss that hot/cold water freezing, including this one:
http://www.urbanlegends.com/science/hot_water_freezes_faster.html
On a comment made earlier in this thread about heat and light - once light strikes an opaque object, it is converted into heat. That is true of the other frequencies in the electromagnetic spectrum unless the energy is turned into chemical energy (I guess it could also be turned into some other form of energy also, but in a house it will either warm the walls/floor/occupants or be used by the house plants...) Remember that old high school physics mantra - "energy can be neither created or destroyed, just changed in form" (unless we are doing atomic fission or fusion)...
And an additional bit of trivia regarding the comment on the efficiency of an automobile slowing down and speeding up. Actually, a couple of decades ago some folks that set a then record gasoline mileage of something like 245 mpg actually did accelerate up to something like 25mph and then coast down to about 5 mph and then start the engine and accelerated up again. I think I read some other accounts of people trying to set gasoline efficiency records who used the accelerate/coast method rather than keeping a steady speed.
A few months ago I read an interview in one of the science magazines with a lady who was supposedly one of the leading experts on fuel economy and she said that, contrary to common believe, you actually get better gasoline mileage in city driving if you accelerate at about 2/3 throttle to get up to your cruising speed rather than accelerating more slowly. Of course if you zip up to speed only to slam on your brakes, that ain't gonna do much for your gas mileage...
I don't want to get into an extensive theoretical discussion but I'd like to point out that small temperature differences can result in significantly more radiant transfer than the same differences in conductive or convective transfer. This is because radiant transfer is a 4th power function of the absolute Ii'e., Kelvin or Rankine) temperatures, thus a difference a few degrees can cause a relatively large difference in the heat transferred. For instance taking skin temperature to be about 95 F. a surface at 110 degrees (570 Rankine give or take a tenth) will gain heat proportional to the 4th power of the temperature difference. ie. (570^4 - 555^4) or 10,680,609,375. Lower the temperature of the heating surface 5 degrees to 105 F the number comes out to7,025,200,000. This means you have lowered the RADIANT heat transfer by a factor of 35%. So small differences in surface temperatures result in significant differences in the radiant heat transfer.
Radiant is the greatest factor in comfort. It is why I am perfectly comfortable in my shirt sleeves here in CO at 45 when the Sun is shining, but uncomfortable as soon as it clouds up. The most effective thing you can do to increase comfort in a chilly space is to raise the average surface temperature of the surroundings. Have you ever been next to a single pane window when it's below zero? Change it out to a double pane and you have raised the inside surface temperature of the glass from about 17 (did you notice the frost on the window) to about 47. Increasing ceiling R Factor from R19 to R40 will raise the surface temperature from 68 to 69 roughly and I'll leave it to you to work out the radiant ratio. Because of the large view factor though the ceiling has a great effect and I'm now getting too deep technically, but try sitting a the kitchen table with your legs under the table in a house with radiant electric ceiling heat when it is cold outside.
I don't mean to hijack this thread, but since there seem to be some people with an understanding heat loss physics what should you set back your thermostat to. I read an article that stated if you set back (at night or during the day when your at work) more than 5 degrees you will use more energy getting the temp up than you saved. The article said that 5 degrees was as low as you should set the set back temp. Is this true. I live in Chicago.
No, it's not true. You can set the thermostat back as far as you like, consistent with not letting the pipes freeze. When I put my programmable thermostat in, I was using a 12 degree setback at night and 15 - 20 in the daytime, normal heat for an hour in the morning and 4 or 5 hours in the evening. I saw a dramatic reduction in my gas bill. You could do it manually, but I really like the programmable thermostat because it can warm up the house while I'm driving home. In fact, it even doubled as an alarm clock. Under all the blankets it took to stay warm at 60 degrees, when the temperature hit 70, I was throwing off the blankets and waking up.
There's a guy here in Colorado who has been carrying on a multi-year crusade to get the public utilities commission to force the gas company to send out a notice in their bills admitting they were lying when they advised people they wouldn't save any more money with setbacks of more than 5 degrees. He claims the scientific guys at the gas company have admitted to him that they know he's right, but the company is still resisting telling the customers about it.
It depends. What is your construction like. If you live in an old row house with solid brick walls, you probably can't save much. The mass of the house will be very difficult to bring back to temperature. If on the other hand you live in a well insultated frame house with light weight gyp board, you can probably set it back 10-15 degrees.
The amount of savings varies with your life style. If there is no one in the house for 8-10 hours and you also set back when or before going to bed it can be significant. I use to only warm up the house to 60 in the morning, now my DW requires it be 70 before she will get out of bed! I would also set back at night and during the day to 50, now it is 60 so like i said it depends!
Thanks. I have a 1931 2 wythe brick bunglow with a 1960 boiler for the first floor hot water heat and a 1999 forced air furnance for the second floor (renovated attic). It takes a couple of hours to get the first floor up to temp (came home early with a cold and froze my butt off for two hours waiting for the house to warm up). The solid brick walls are great in the summer but not so nice in the winter.
Archy,
With an old house, masonry construction and either hot water or steam heat (steam is more responsive than hot water), using set backs requires a little more understanding and planning than in a frame house with forced air. You can still do, but as you found out, the response time involved in an unplanned change in use can be uncomfortable.
Night setbacks have been used to reduce energy consumption longer than I have been alive. Old pneumatic systems did it up until the 70's and 80's. The physical principles that govern heat loss are simple. The energy loss is UAdT, where U is the recip of R, A is the area of the wall/window/ceiling etc., and dT is the temperature difference. In Chicago, -10 is common and -15 is normal design outside air temperature. If you keep is 70 inside when occupied, and 60 inside when unoccupied, dT changes from 85 to 75. This would reduce the energy loss (by transmission only, there are other factors involved) by over 11%.
Whomever stated that the temperature reduction should only be limited to 5 degrees does not have your energy costs in mind.
The example I always use is an air compressor with a leak. The higher the pressure, the faster the leak. Lowering the pressure reduces losses and the pump runs less, but recovery to the higher pressure takes a while, although during the drop to the lower pressure the pump unit doesn't run at all. In the end, you waste less air [heat] letting it drop to a lower pressure [temp] for a while. In the end, all the heat introduced into the building leaks out (assuming steady-state cold and dark), it's only a matter of how fast.Be seeing you...
Ah, but Tim: my hot water heater is electric. So no heat is lost from the house.
Ok, so you don't loose any on efficiency. Do you heat your house with electric resistence heating? The efficiency is high, but so is the the cost. If I were paying the electric bill to heat that tank of water, I would want to keep as much of that heat in the water. I had an all electric house, with electric baseboard heat and an electric water heater, electric dryer. The first January in this house in northern IL, I had a $400 electric bill. Now, converted to LP, that $400 will cover November, December, January and Febuary, if its real cold.
John -
I agree with Bill here: electricity is converted to heat pretty efficiently thus baseboard heaters work well.
Do you mean instead that the generation and transimission of electricity is inefficient as a means of producing power? and thus using it to produce heat is overly expensive compared to other means? 'Cause I would agree with that.
Ed
Actually, there is a difference in efficiency. First of all, a red-hot wire converts a sizeable part of its' energy to light- not heat. Secondly, there is a type of "inertia" at work; that is, it's a lot more efficient to heat a lot of air a few degrees, than it is to heat a little air a lot. In essence, a lot of the heat imparted by that red-hot wire to the air goes directly outside, without pausing to heat anything else in the room.
"First of all, a red-hot wire converts a sizeable part of its' energy to light- not heat."
If you have a baseboard heater that is glowing red-hot you should not be on the computer, but rather you should be getting out of the house IMMEDIATELY!
Then call 911 from a neighbors.
"Secondly, there is a type of "inertia" at work; that is, it's a lot more efficient to heat a lot of air a few degrees,
than it is to heat a little air a lot."
Define "efficiency". Define BTU and then tell me how efficiency is affected whether you are heating a small mass a by a large amount or a large mass a by a smaller amount.
"In essence, a lot of the heat imparted by that red-hot wire to the air goes directly outside, without pausing to heat anything else in the room.."
First of all where are you getting this red-hot wire from?
And secondly explaing how the "heat" does directly outside.
all of our solar homes use electric cove heaters as back-up... compared to electric resistance convection heaters, they can offer the same comfort level at a lower thermostat setting .. they have a quicker response time also..
however, this is a marginal difference and i do not think you will ever recover the cost of converting.. nor is the comfort level that much better that i would recommend converting...
given the choice for a new installation, i would still prefer the radiant cove heaters over the baseboard convection heaters... but each has their own peculiarities...
baseboard is easily blocked by furniture.. but the cove heaters mount high on the walll... some do not like looking at them.. no free lunch here either...
better to invest in upgrading your insulation.. or checking for other points of heat loss
Mike Smith Rhode Island : Design / Build / Repair / Restore