Electric resistance heating

[Ehouse]

When circulating fluid for hydronic radiant heating, the larger the radiator (whole floor as opposed to baseboard), the lower the temperature of the fluid required to get to the desired room temp. I assume this is true for electric infloor (or ceiling) heat as well. In the case of hydronics, the lower temps allow geothermal solutions to work, moving heat rather than using on site combustion. Can any one do the calculations for an electric resistance set up to see if there is a savings in total energy usage with a larger radiator to achieve the same room temps?

Ehouse

 

[Highbeam]

That would fall under the heading of..."There is no free lunch".

The total btus required to heat the space is the same with a small hot radiator or a large warm radiator.

 

[btuser]

There's no real loss when it comes to electric heat, so you'd just be spending more money than you need. Comfort? Yes, there could be a difference. I can't think of a situation where it would make sense unless you were going under expensive floor covering and wanted to parallel the circuits JIC one of them fried. Still it may not make sense because I think overheating is one of the main reasons they burn out (some are self-regulating) and have pretty clear tolerances as far as spacing.

The example you give of a larger mass = a lower radiant temp isn't going to transfer to electric heat. With boiler setback you're saving during the shoulder season by not heating to your design temp when its not needed, therefore saving on standby losses, short cycling and the lack of people opening windows to even out the heat. Electric heat is different, and is converted in the conditioned space immediately without loss rather than being pumped from the boiler to the room. Also, the actual mass difference between the two mediums isn't even close (think of a 200lb radiator vs a 2lb toaster). Its either on/off, or you end up with a resistor/xformer and now you're talking loss.

Save the copper. Add more insulation.

 

[Seasoned Oak]

Spot heat is very efficient ,for example i like the bathroom at 80 Deg but i wold not want my whole house at that. So of course i have electric heat in the BR for intermittent use.

 

[Adios Pantalones]

Highbeam hit it for electric heat. The heat it gives off is directly related to the amount your meter spins, no matter how you slice it.

 

[Ehouse]

Thanx for the responses. I am going somewhere with this, so bear with me. So, the relation between heat production and electrical input (watts, joules ?) is 1 to 1, even at extremes, but does that hold true for maintaining a given temp. in a slab ,say? Does it take 10 times less electricity to maintain a given slab temp. of 50* than 500*?

Ehouse

 

[Adios Pantalones]

First of all- there's no such thing as 10 times less electricity. Once you have one time less electricity- you have none. If you are asking- would it take 1/10 the electricity, the answer is no.

Next- the relation is not linear like that. You need to know the DIFFERENCE in temp between the slab and the air/ground around it, as well as insulating values- not just the temp you are trying to hit. Keeping it at 60F in the winter is tougher than in the summer.

 

[btuser]

I think it's linear as long as your differential between indoor/outdoor temps is constant, but depending how your heating medium dissapates heat it probably takes more and more as the temp goes up because the molecules spread out. Kind of like pin holes in a baloon. As you increase the pressure and the baloon gets bigger the holes let more and more air out till you've reached your lung capacity.

Resistance heating is technically all waste heat on the circuit so messing with the output on the same circuit isn't going to change current-to-heat efficiency. It may change your system efficiency, say keeping a slab temp of 80 degrees when its 60 outside and a temp of 90 degrees when its 30 outside, but that can be handled by an outdoor reset controller.

 

[Ehouse]

So, what happens if you consider the slab mass as a fly wheel and only provide a bump of input at intervals, such as an overcharge dump for a wind turbine or micro hydro? Is there an equivalent situation to a hummingbird or bumblebee or well pump needing much less energy input to maintain operation than to start up?

Ehouse

 

[btuser]

It takes more energy to heat it up but once its hot the amount of heat to keep it there is relative to the differential you're looking for.

In a nuclear reactor the composition of the fuel rods counts on either positive or negative neutron displacement in reacton to the temperature of the fuel. This can be predicted and therefore design safety is achieved via known parameters.

I have no idea how many hummingbirds it takes to cool a nuke plant.

 

[gtjp]

But our finch does DISTRIBUTE room air heated, in paths under its wings to objects which radiate heat energy back to objects receiving and then smiling and then enjoying and then releasing energy to feed the finch and and and ...etc etc etc...

Experienced with Up State Ohio 6600 deg days, 27 below JAN 18-19 1994...
Data tracking since 1980: Heat load sheet www.GEOPros.org (click logo header)

Your first statement:
"When circulating fluid for hydronic radiant heating, the larger the radiator (whole floor as opposed to baseboard), the lower the temperature of the fluid required to get to the desired room temp."
-
as written- certainly is accurate as it stands,
if every sq ft is desired to be heated.
And this is not considering what warmer air is floating above the heads of occupants , say standing in the area.
A smaller hx area radiator
at a higher temperature may "feel-warm" in that area nearer/over the smaller radiation sq ft.
---
However, EVEN AT SAME TOTAL ROOM COMFORT just above the occupant(s) , there would be MORE ENERGY required for other reasons others have noted in comparisons:
1 being- more warm convected-air stratifies above smaller radiators -in a space heating situation
if
there's no circulation from say a high return grill positioned well enough, or a no ceiling fan to slowly push downward, avoiding wind chill.
(Fans to NOT EVER BE PUSHING AIR UPWARD UNDER COLD PARTITIONS.)

Stratified ceiling air is found resulting in higher temperature thinner layers of air, + moving MORE HEAT ENERGY out of the SAME SPACE (at colder ceilings).
Radiators (if smaller, same energy output totally) along walls, near walls have similar higher heating energy requirements, I have found.

Per sq ft flooring, I believe you will find it is NOT LINEAR, in spacial energy required.

SIDE:
Circulated air for cooling in large stores is as low as 2.1/4 room air changes at the height of only 8-9ft off floors where occupied with mid-high return air intakes, for least energy of cooling...saves energy.
But
about 3- 3,1.2 air changes in a HEATING application- is for a whole room space comfort say volume considered divided by 17, for CFM of high return-to-supply).
OR
like a lake-bubbler thermal turn-over system (upside down):
= A small 40-watt 6"dia to 4" reducing nozzle ducted circulator can sufficiently return warmer ceiling air DOWNWARD to floors (about 2.1/2 ft per sec at near flooring) , and if not disturbing cold wall and ceiling partitions boundary-layer-air (laminate-air near surfaces of walls left in place, etc.) placed 8-12 ft from walls (or downward registers vanes positioned same) --- can all turnover the air with 1-3 degree floor-ceiling differences in vertical air stabilizing 'spots' every 20-25 ft apart.

 

[btuser]

You're assuming another variable. We're not comparing radiant vs warm air vs baseboard. The question was will 2x as much electric radiation provide a cost savings similarily found in oversized baseboards or other medium. You can double up the tubing in a radiant slab to lower your needed differential and that can gain you efficiency, but electric heating doesn't work like that. Lowering your operating temperature is not going to give you combustion/transfer efficiency gains. I guess with an electric boiler it could, but that's cheating cuz you're really using water and just heating it another way. 2x the element in this case would be a total waste of money.

 

[Ehouse]

Is there such a thing as DC resistance heat?

Ehouse

 

[btuser]

Is there such a thing as DC resistance heat?

Ehouse

http://www.oemheaters.com/t-dc-powered.aspx

 

[Ehouse]

Excellent link! Thank you btuser. So, in an off grid situation you can have ERH without an inverter. If you're grid tied and the grid goes down, (or if your inverter fries), you could:bypass your inverter and/or charge controller and still have ERH. Very interesting.

Ehouse

 

[Ehouse]

It's been costing me about 20 to 30 dollars /mo. extra on my electric bill to run 2 oil filled rads. @ 1500watts ea. plus 1 @ 650watts. Not continuous at full wattage by any means. These take care of 1,000 sq.' upstairs in a poorly insulated 1890's Victorian and supplement a smallish woodstove downstairs. A small DV propane stove kicks in at the far end of the downstairs if the woodstove needs help ( below 20*F outside). Seasoned Oak stated that electric spot heating is very efficient. I agree, and it makes me wonder why people spend so much money on complicated heating/distribution systems given the advantages of this type of heating. What is the monthly cost in electrical usage to run a heat pump (ball park) or a furnace? The service/ delivery charges on my electric bill average half the total and I'm sure will only rise in the future. As we've established above, ERH combined with simple one time cost technologies like super insulation and passive solar gain could work very well, even in an off grid app.

Ehouse

 

[btuser]

Definately passive solar. Best ROI you can hope for. Thermal solar too (hot water etc) is up to 30% efficient vs 12-15% for panels, and a hot water tank is a heck of a lot cheaper than batteries.

 

[Ehouse]

Another sleeper is micro hydro. Wonder why it is ignored for subsidies (at least in NY). Wonder why no subsidies for any off grid elec. production (not).

Ehouse

 

[sesmith]

it makes me wonder why people spend so much money on complicated heating/distribution systems given the advantages of this type of heating. What is the monthly cost in electrical usage to run a heat pump (ball park) or a furnace?
Ehouse

For me, buying a ground source heat pump was due to a back injury that forced me out of cutting and heating with firewood anymore. Since putting it in in Oct of last year, it's cost us about $250 total to heat our house. This is a house that normally would use 6 full cords of wood or close to $3k of oil if we used the previous oil furnace (avg winter...this one has been warmer than usual). With the wood stove we had a lot of cold spots (one of them being my living room). With the heat pump, the house stays within a degree of 67 (where we like to set the tstat), and all rooms are within a degree of each other. We don't set the temperature back (heat pumps work better this way) and we're heating the whole house instead of closing areas off in cold weather. The heat pump did cost a lot, but will pay for itself in short order with fuel savings. Knowing what I know now, I'd never go back.

 

[woodgeek]

it makes me wonder why people spend so much money on complicated heating/distribution systems given the advantages of this type of heating. What is the monthly cost in electrical usage to run a heat pump (ball park) or a furnace?
Ehouse

In very round figures, for the East Coast, electric resistance heat currently costs about the same per BTU as oil heat or propane, a heat pump south of NYC, or in maritime climates runs about 40% of that, getting stil cheaper as you go south, while geo or nat gas runs only 25-30% as much as oil/elec/propane. IOW, if you have nat gas, it is hard to beat. Geo or heat pump can reduce operating costs a lot. Folks spend the money to save money.

 

[Ehouse]

Sesmith, as you know from above posts I have a GHP waiting to be installed in a house I'm building. I hope my numbers come in that good. To clarify my situation, the housing market crash left me with 3 unsaleable homes and one under construction, all with different heating systems. This thread is an attempt to explore ways to incorporate ERH with it's clear advantages into some or all of these heating situations. As woodgeek says and I had suspected, ERH is about equal in (operating?) cost compared to conventional heating technologies in upstate NY, and the balance is becoming more favorable all the time. Heck, my neighbor is paying $250.00/ton for pellets. That's as much as your entire heating bill since Oct. The costs for equipment, installation and to maintain these systems is prohibitive. Here are my strategies to date for each house.

-1,000 sq.' apartment on 3 levels in 1/2 of an owner built utility building:

Rented to nephew.
Power vented propane furnace, not in use.
electric baseboard backup seldom if ever used.
propane DV fireplace, works great.
Wood stove in basement free firewood for him from my woodlot ( Little SOB's taking all the dead Locust!)

-2,4000Sq.' House under construction on same prop. as above.

ICF poured concrete with tubing in poured basement and first floors. Upper level to be faster response in floor heat (subject to
change).
Two stage GHP for heat and AC run from pond loops.
Well situated for solar, wind and/or microhydro.
Sunspace with lots of glass to the southeast. On sunny winter days I'm thinking I can run the circulators only to distribute heat from
the dark sunspace floor to the rest of the house (or at least the main floor). Light colored throw rugs will cover floor in summer.
400 ft from above house so I will run a 60 or 100 amp feeder avoiding an added service charge and establishing a grid tie to qualify for
subsidies (said nephew is getting his installer's license for solar).
I'm thinking a small LPG fireplace with a soapstone surround for ambiance and supplimental heat. Maybe some ERH elements in it
as a heat dump for microhydro.

-1817 house reworked in the 70's by my dad. well insulated.

Elec. baseboard throughout. Class A chimney installed. Woodstove installed by tenent at his request (stupid! stupid! stupid!, had to
rip it out as he put in a used smoke pipe with holes in it!) Intend to replace it with a nice DV LP stove.

-1890's Victorian moderate/poor insulation ( blown in walls, attic not bad).

Current residence. Small EPA wood stove. Small DV LP stove. 3 oil filled elec. radiators for upstairs. Moderately efficient LP boiler
for DHW. Boiler also runs a fan coil in old furnace plenum for backup. Heating bill very low since installation of wood stove ( saved a
about $3,000.00 this year.

Please feel free to comment or criticize.

Ehouse

 

[woodgeek]

Aaah, now I get it. Yes, I was discussing operating costs only, not amortized equipment or anything like that. For a rental property w/o access to gas, and so far north, electric resistance is a fine choice....it will prob be hard to beat it with oil or propane, and has lower install and maintenance costs, and safety for the tenants is a nice plus. You might check to see if the local utility has an 'electric heating' discount rate and tip off your tenants....these are getting phased out, but I think they still exist in places.

 

[sesmith]

Actually, I didn't remember the geo, just was answering the question you put in one of the posts above. Sounds like you have your hands full of heating systems. I hear you about having a rental with a tenant installed stove in it. My neighbor rents out his house...I've seen the chimney light up the sky over there before (went over to make sure they were ok). Not that a chimney fire can't happen to anyone, just that tenants don't always take the same care as the owner would.

Wood's saved us a pile of money over the years for me. I cut it from my woodlot until last year. The gshp is working better than I ever expected. Of course it's been warmer than usual this year, but not that warm.

Only suggestion...on your victorian, if you haven't done it already, do as much air sealing in the cellar and attic areas as you can. Most of those were balloon construction, if I remember right. Great chimney effect air leakage up the walls.

 

[maple1]

Have a friend who put in Geothermal last year. Last time I talked to him about it mid-winter, he was looking at +$250/month on his electric bill. I'll have to look him up and get an end of season report, after the season is over.

 

[Ehouse]

I love my little wood stove. It's saved me a ton of money and is very enjoyable to operate. Another advantage with a drafty house; just throw on a little more wood! My Victorian is a modified post and beam, as is my dad's old place (Chestnut beams with stud infill), so little chimney effect. Lumber was relatively cheap back then. Air sealing is ongoing.

After monkying about with many different heating systems, including helping to install several state of the art mod-con boilers (pricey!). I'm becoming convinced that wood heat with electric backup is the way to go. I won't give up my Geo., but it's another kettle of fish with high installation, equipment and maintenance costs. An added benefit of ERH is it's potential to be produced on site, and although no one's going to heat their house totally with solar panels, combining with superinsulation, individual room insulation, maybe some solar hot water and other strategies looks very competitive to me.

I have another question about ERH that's been bugging me. I keep reading that a watt is a watt is a watt and that's end of story as far as efficiency is concerned. My father's place (see above) has elec. baseboard (220) installed throughout. It is expensive to keep it up to temp. and yet I can keep it quite warm with 2 or 3 oil filled rads. (15,000btu ea.). There must be some hidden inefficiency here. I suspect that the heaters were engineered to sell product like every thing else out there. Does elec. baseboard suffer from the same short cycle problems as an over sized furnace? Is there a start up surge penalty as with an electric motor? I'm thinking they were set up like an old style furnace; over sized and on thermostats to switch on /off instead of modulating or constant low grade on. Comments?

Ehouse