Heat pumps

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Jim W in Tampa said:
Just tried out my heat pump on my my family room 800 sq feet 3 1/2 ton and very impressed on its output at 24 amps/240.Are they really more cost effective ?
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Jim, you have 3 1/2 ton for only 800sq ft? I have 3 ton on a/c handling over 1600sq ft. The "rule of thumb" I have always been told is 1 ton per 800 sq ft. I am also assuming that your location you do not have heat strips in the unit ether
 
Jim that is a bit of a hard question to answer because it depends on many factors most importantly cost of gas vs electricity, and the temp differential between outside air and inside.

However I will fgo out on a limb here since I believ you are in Tampa FL, a heat pump is your most economic heat source. I base that on your are is highly unlikely to ever drop below 35 degrees and need backup heat.

When you compare btu's between a heat pump vs electric strip heat for a given kilowatt, the heat pump wins out by about a 3 to 1 ratio say above 45 degress outside air temp. However by the time the temp drops to 32, the ratio is equal. Below 32 the heat pump looses the battle, and below say 20 is useless.

To really narrow it down you have to look at few factors, how much is your electric rate per BTU vs NG price along with the differential temp. In my area NG is dirt cheap and electric is expensive so NG heat wins out at any temp.

If you live in a northern climate, forget a heat pump unless you have dual source like heat pump when outside air is above 35, and gas backup when temps drop below 35.
 
3.5 tons for 800 sq feet?:-?

I never bought the efficiency thing, at least as far as power consumption. I mean, you are just running you AC backwards. The thing has to run longer than a gas furnace because the heat is nowhere near the same.

If natural gas prices are high or you have to rely on trucked in fuel maybe it would be less expensive.


And yeah...comparing it to strip heat, it would HAVE to be cheaper.
 
dereckbc said:
When you compare btu's between a heat pump vs electric strip heat for a given kilowatt, the heat pump wins out by about a 3 to 1 ratio say above 45 degress outside air temp. However by the time the temp drops to 32, the ratio is equal. Below 32 the heat pump looses the battle, and below say 20 is useless.
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Its not that bad. Most modern heat pumps have a coefficient of performance (COP) over 3 at 30F and over 4 at 50F. At 0F, the COP should still be near 2. So the pump is still always better than strip heat down to 0F (and I think most manufacturers don't recommend running them much below this). The variable that is difficult to quantify is defrost. That lowers the effective COP, but if your heat pump can defrost with some decent logic, that can minimize the inefficiency.

For a 2007 unit COP, see page 25 of this link: http://www.yorkupg.com/PDFFiles/345094-YTG-C-1007.pdf

Or page 12 in this one: http://www.goodmanmfg.com/Portals/0/pdf/SS-SSZ16.pdf
 
The more popular, expensive, heat pumps in this area use water instead of air. Either pump and dump, or in a closed loop system. Rarely need to actually use the backup heat plus hot water options are available. Water features are now more common because of the pump & dumps.
 
dereckbc said:
Jim that is a bit of a hard question to answer because it depends on many factors most importantly cost of gas vs electricity, and the temp differential between outside air and inside.

However I will fgo out on a limb here since I believ you are in Tampa FL, a heat pump is your most economic heat source. I base that on your are is highly unlikely to ever drop below 35 degrees and need backup heat.

When you compare btu's between a heat pump vs electric strip heat for a given kilowatt, the heat pump wins out by about a 3 to 1 ratio say above 45 degress outside air temp. However by the time the temp drops to 32, the ratio is equal. Below 32 the heat pump looses the battle, and below say 20 is useless.

To really narrow it down you have to look at few factors, how much is your electric rate per BTU vs NG price along with the differential temp. In my area NG is dirt cheap and electric is expensive so NG heat wins out at any temp.

If you live in a northern climate, forget a heat pump unless you have dual source like heat pump when outside air is above 35, and gas backup when temps drop below 35.
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I say, heat pumps should not be used ANYWHERE where electricity is higher than the national average. Once you have to suffer the installation costs of backup NG or Oil heat, the cost-benefits of a heat pump goes out the window.
 
In Tampa i will seldom dip under 50 and usuallynot even that cold.The 3 1/2 tons are because of the large crouds we entertain ,sometimes up to 70.The fan has multi speed to back its over kill down as needed.Also has heat strip if needed.I simply was surprised at amount of heat while only pulling 24 .4 amps /240.Electric here is from progress energy and is about 12 cents per kw
 
Jim W in Tampa said:
Just tried out my heat pump on my my family room 800 sq feet 3 1/2 ton and very impressed on its output at 24 amps/240.Are they really more cost effective ?
Click to expand...

Having been in the a/c business, I do not think you have 3.5 tons in 800 sq ft. If you do, you got the shaft and the a/c is not gonna work. It will turn on for about 5 min, cool of the room and shut off. You willl not get any dehumidification. Sized right, they are very effeicant. Your is not because 3.5 ton will heat and cool a 2800 sq ft house.
 
LawnGuyLandSparky said:
I say, heat pumps should not be used ANYWHERE where electricity is higher than the national average. Once you have to suffer the installation costs of backup NG or Oil heat, the cost-benefits of a heat pump goes out the window.
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I disagree if you still want airconditioning. The heat pump is cheaper to run than oil. Gas gets closer, but it all depends on your local rates. The problem is the auxillary heat. Resistance heat will kill you cost wise if your electricity is expensive. This is moderated by the fact that the heat pump can run with the resistance heat though somewhat lowering the cost. Most dual fuel systems turn off the heat pump at some cut over temperature. So the efficient heat from the heat pump can't be used with the fossil fuel system.

The cost benefit analysis really depends on how cold it gets in the winter and whether a heat pump has any hope of producing enough heat the majority of the time. If you really need 80K-100K BTU of heat most of the winter, you'd be better served by a gas or oil system. In my area, I need 49K BTU of heat at the winter design temperature -- that's right in heat pump territory.
 
I don't think anyone North of D.C. qualifies. Unfortunately, builders discovered this system could provide A/C AND heat for just a little more than the cost of A/C alone, and so favored the system over anything that required a different fuel and a chimney. Kept their costs low by sacrificing running and maintainence costs borne by the owner.
 
Jim W in Tampa said:
In Tampa i will seldom dip under 50 and usuallynot even that cold.The 3 1/2 tons are because of the large crouds we entertain ,sometimes up to 70.The fan has multi speed to back its over kill down as needed.Also has heat strip if needed.I simply was surprised at amount of heat while only pulling 24 .4 amps /240.Electric here is from progress energy and is about 12 cents per kw
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You are exactly right Jim, the math does not seem to work, but there is a good explanation for the discrepancy. Your wattage (assuming a power factor of one or near one), is 24.4 x 240 = 5.86 kw. This is equivalent of around 20,000 BTU/hr, or about 1.7 tons. The fact that you get 3.5 tons from the heat pump represents a Coefficient of Performance (COP) of around 3.5 / 1.7 or about 2.1 This means you get around 2.1 units of thermal energy for every 1 unit of electrical energy spent. Strange as it sounds, it does not violate conservation of enery law, as you are using the electric energy to simply move heat from one place to another, and not converting electric energy to heat directly. Ground source heatpumps are even more impressive than this, as they have a much better COP than the air-source heatpumps. Heat pumps are almost always cheaper than resistive electric heating (they degrade to the efficiency of resistive heating, once the auxiliary heat comes on in very cold weather). e/m
 
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Cavie said:
Having been in the a/c business, I do not think you have 3.5 tons in 800 sq ft. If you do, you got the shaft and the a/c is not gonna work. It will turn on for about 5 min, cool of the room and shut off. You willl not get any dehumidification. Sized right, they are very effeicant. Your is not because 3.5 ton will heat and cool a 2800 sq ft house.
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I agree its too large but i did the install myself.I run a small club and it gets packed with couples and it has a dance floor with a pole for the girls.Also must deal with the slider door to hot tub area will get opened often.Once its cooled down the main house AC 3 ton keeps it to 76.All totalled i am cooling almost 2900 sq feet,half of it 24/7 rest only on saturday nights.Its very importand to be able to keep the people feeling cool.My AC friend has suggested i run the blower at slow speed to help.Heat pumps are new to me so really had no idea what to exspect.My 10 kw on main house never put out near this much heat.
 
Jim W in Tampa said:
I agree its too large but i did the install myself.I run a small club and it gets packed with couples and it has a dance floor with a pole for the girls.Also must deal with the slider door to hot tub area will get opened often.Once its cooled down the main house AC 3 ton keeps it to 76.All totalled i am cooling almost 2900 sq feet,half of it 24/7 rest only on saturday nights.Its very importand to be able to keep the people feeling cool.My AC friend has suggested i run the blower at slow speed to help.Heat pumps are new to me so really had no idea what to exspect.My 10 kw on main house never put out near this much heat.
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The pole alone will probably consume half of the cooling capacity... ;)
 
Jim W in Tampa said:
I agree its too large but i did the install myself.I run a small club and it gets packed with couples and it has a dance floor with a pole for the girls.
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Well I am not going to say much about that, but you earlier said crowds of 70 people. With that many people in such a small space shouldn't require any heat. :D
 
dereckbc said:
Well I am not going to say much about that, but you earlier said crowds of 70 people. With that many people in such a small space shouldn't require any heat. :D
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Actually its because of body heat that you need to increase the AC size.And with the added antifreez (drinks) few will get cold.Heat is mainly needed for the clean up work next day.
 
Jim W in Tampa said:
Actually its because of body heat that you need to increase the AC size.And with the added antifreez (drinks) few will get cold.Heat is mainly needed for the clean up work next day.
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I can vouch for this. Heat for about 30 minutes to take the chill out when you open, and later during cleanup. Bar crowds have a way of staying warm....
 
Jim W in Tampa said:
Actually its because of body heat that you need to increase the AC size.And with the added antifreez (drinks) few will get cold.Heat is mainly needed for the clean up work next day.
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I read somewhere that average person puts out equivalent of 80 watts of heat when at rest. The amount output goes to near 150 watts when exercising (e.g. dancing). Based on this, and figuring 100 watts average per person and 70 persons present, it is 7 kw, or a little over 2 tons of heating capacity. Not bad considering it is free heat source! e/m.
 
Energy-Miser said:
I read somewhere that average person puts out equivalent of 80 watts of heat when at rest. The amount output goes to near 150 watts when exercising (e.g. dancing). Based on this, and figuring 100 watts average per person and 70 persons present, it is 7 kw, or a little over 2 tons of heating capacity. Not bad considering it is free heat source! e/m.
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It is bad in the summer and even in the winter the AC will need to run some.The walls are about r 30 and 1 foot thick,keeps the toons from being a problem to neighbors.System can putout about 1 kw.At about 4 pm it was in the low 60's outside.Raised the room 6 degrees in about 15 minutes.
 
Energy-Miser said:
I read somewhere that average person puts out equivalent of 80 watts of heat when at rest. The amount output goes to near 150 watts when exercising (e.g. dancing).
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I must be a high-efficiency unit. I rarely wear a jacket outside, I'm always warm indoors, and when PJ puts her cold feet on me, we both say, "Ahhh!" She calls me her electric blanket.

Based on this, and figuring 100 watts average per person and 70 persons present, it is 7 kw, or a little over 2 tons of heating capacity. Not bad considering it is free heat source! e/m.
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It's not free at all. You have to feed the generators: Wings, chips, quesadillas, etc., etc., etc.

Now, if you're charging for the fuel, that's another story. ;)
 
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