In a link from http://www.energyland.net/, How Emergency Power Systems Work, some figures are given for heat pumps/airconditioners:

Whole-house A/C or heat pump--15,000 Watts; surge = 30,000 watts.

I have a fairly large house, and opted to install a "ground source" heat pump. This system uses groundwater, rather than outside air, as the source from which it "steals" heat or cold, placing this stolen energy into the house.

Because of the steady temperature of the groundwater (in my case it is slightly over fifty degrees fahrenheit), this type of heat pump operates far more efficiently than a "normal" heat pump. In fact, my heat pump, which is classified as a "three ton", only draws 3400 watts, as compared to 15,000 watts given in the example, above.

My heat pump operates at almost 400% efficiency! It works so well that I can hardly believe it. It is manufactured by Water Furnace.

I also have wood heat, which is my preferred source of heat, and environmentally the most friendly of the common heat sources, IMHO, but it's nice to have the heat pump there to warm the house before I wake up, and keep the house at whatever temperature I choose whenever I'm out of town.

-- jumpoff joe (jumpoff@echoweb.net), January 17, 2000

Answers

Joe - I'm assuming you have a fairly high water table - but I'd be very curious to hear some more specifics. The community college in our area recently installed (with a lot of grant / demonstration project money, I'm sure) a geothermal system similar to what you describe.

I am very blown away by your three ton unit only drawing 3400W! But then, I'm sure that's a result of using geothermal, and that the heat extraction process itself is much more efficient (hence the lesser power requirements to run the unit)..

-- Rick Cowles (rick@csamerica.com), January 18, 2000.

Rick, I have a sometimes flowing artesian well, it is true, but that has little bearing on this system.(For that matter, my house is up hill from the well, and my storage tank is over 100 feet higher than the well head. I have a 1/2 hp. pump, 240 volts, which produces 10-12 gpm, depending on well drawdown which can be as much as 28 feet at the end of the irrigation season) Obvously, if one had to pump from several hundred feet down, the pumping costs would become significant. I did not, in fact, include pumping costs, as in my case, they are almost negligible.

One reason "regular" heat pump power use is so much higher than "ground source, aka geothermal" is that, when the outdoor ambient air temperature gets cold, (depends partly on relative humididty, but generally seems to become important in my climate whenever the temperature drops below about forty degrees Farhenheit) the outdoor condensor begins to develop a coating of frost, which reduces heat exchange efficiency. To counter act this, the unit is forced to heat the outdoor unit to sublimate or melt the frost. The way this is done is to reverse the heat pump, making it into an air conditioner. Heat goes to warm up the outdoor unit, cold air is blown through the ducts. To avoid the interior temperature of the house dropping drastically (after all the air conditioner is running!) the heat strip turns on. This heat strip is the king of kilowatts!

Since the geothermal unit never has any condensation probems, being as how it sits inside the house (the basement in my case)) and being also as how the heat source is water which is nearly a constant 50 plus degrees fahrenheit, the unit never has to run in the air conditioning mode during the winter.

My three ton unit is on a thirty amp circuit, with ten gauge wire. There IS no heat strip. The only reason you might want a heat strip is if there is no backup heat source. Let's say the compressor has a breakdown. And you have no backup. And it's cold outside. In this case, a heat strip would provide you with "emergency heat" until such time as your friendly neighborhood HVAC repairman got your compressor repaired or replaced. I have a wood heater, so I opted to save a couple of hundred bucks by not having to install the emergency back up heat source, the extra breakers, and all that expensive (six gauge copper) wire.

My HVAC subcontractor and I actually measured the power draw while the unit was running. It was drawing 14 amps, which is how I arrived at 3400 watts (14 amps times 240 volts =3360 watts) (I rounded up to 3400 watts) By the way, this particular unit uses 4.5 gallons of water per minute whenever it is running, which in my case is about two or three hours per day, usually. You can adjust the water flow rate. Using more water makes the system slightly more efficient, but wastes water and, obviously, increases pumping costs. Using less water than 4.5 gpm. saves water, lowers pumping costs, but decreases efficiency. When I have adjusted the flow rate up to about 7.5 gpm, just to see what happened, the air coming out of my floor register went from about twenty degrees higher than house temp to about twenty five degrees above house temp. (This is a lot higher than my next door neighbor's increase with his "regular" heat pump, which only raises the temp abotut four or five degrees above house temp when outdoor ambient temps are in high thirties, he tells me.)

Rick, I too am amazed that this three ton unit uses only 3400 watts, since this is only slightly more than the use of two portable 110 volt electric heaters. (1500 watts each) In fact, when my wife has asked if she should turn on a portable heater to warm her art studio a few degrees when she hasn't had it heated for a few days, I say, heck no, turn up the heat on the whole house! The heat pump provides four times as much heat per dollar spent than the portable heater!

A couple of other points, for those who may be interested:

There are two basic types of systems available for a geothermal heat pump--closed loop and open loop. Mine is an open loop, as the water is not recirculated. A closed loop either runs water (with food grade antifreeze mixed into it, I THINK) in a loop down into the water in your well, or runs a water/antifreeze solutionn through several hundred feet of pipe buried about (in this area) five feet deep.

The advantage of the open loop system is it is cheaper to install, (tho you may need to drill a return well to avoid depleting the groundwater, if you don't have water running out onto the ground all winter, as I do.) Also the closed loop system remains equally efficient all year, as the groundwater temp remains constant.

A closed loop is somewhat less efficient, because the recirculated water gradually cools off throughout the winter, thus reducing the efficiency until it may even be as low as a "regular" heat pump.

To have a successful open loop system, it is necessary to have fairly good quality groundwater, so as to not have rapid mineral buildup, which is not a consideration in a closed loop system, since the water/ antifreeze solution is made up with high quality water anyway.

I also recommend a copper-nickel heat exchanger for an open loop system. Apparently I may have to "acid wash" my heat exchanger (although I have had no noticeable drop in efficiency after over two years of operation), and the copper-nickel exchanger will take acid washes better without dissolving, or something.

In the summer time, you can only imagine how efficient this unit is, considering it is using 50+ degree water rather than 90+ degree air to dump excess heat from the house into! (I almost wish I hadn't done such a good job designing the house; I've only had to use the air con part of the heat pump maybe ten or fifteen hours so far in over two years)

By the way, on another subject, you can save big $, in low humidity climates (like here in Oregon in the summer) by installing a whole house fan. I can drop the house temp by ten or twenty degrees in as many minutes if I turn on my "attic" fan when I get up at four of five in the morning (54 year old prostate, you know). This is because the dirunal temperature range in this type of climate can be up to about fifty degrees. When I can get the house down to maybe sixty degrees early in the morning, it doesn't really get very hot all day.

-- jumpoff joe (jumpoff@echoweb.net), January 19, 2000.

Rick, I have a sometimes flowing artesian well, it is true, but that has little bearing on this system.(For that matter, my house is up hill from the well, and my storage tank is over 100 feet higher than the well head. I have a 1/2 hp. pump, 240 volts, which produces 10-12 gpm, depending on well drawdown which can be as much as 28 feet at the end of the irrigation season) Obvously, if one had to pump from several hundred feet down, the pumping costs would become significant. I did not, in fact, include pumping costs, as in my case, they are almost negligible.

One reason "regular" heat pump power use is so much higher than "ground source, aka geothermal" is that, when the outdoor ambient air temperature gets cold, (depends partly on relative humididty, but generally seems to become important in my climate whenever the temperature drops below about forty degrees Farhenheit) the outdoor condensor begins to develop a coating of frost, which reduces heat exchange efficiency. To counter act this, the unit is forced to heat the outdoor unit to sublimate or melt the frost. The way this is done is to reverse the heat pump, making it into an air conditioner. Heat goes to warm up the outdoor unit, cold air is blown through the ducts. To avoid the interior temperature of the house dropping drastically (after all the air conditioner is running!) the heat strip turns on. This heat strip is the king of kilowatts!

Since the geothermal unit never has any condensation probems, being as how it sits inside the house (the basement in my case)) and being also as how the heat source is water which is nearly a constant 50 plus degrees fahrenheit, the unit never has to run in the air conditioning mode during the winter.

My three ton unit is on a thirty amp circuit, with ten gauge wire. There IS no heat strip. The only reason you might want a heat strip is if there is no backup heat source. Let's say the compressor has a breakdown. And you have no backup. And it's cold outside. In this case, a heat strip would provide you with "emergency heat" until such time as your friendly neighborhood HVAC repairman got your compressor repaired or replaced. I have a wood heater, so I opted to save a couple of hundred bucks by not having to install the emergency back up heat source, the extra breakers, and all that expensive (six gauge copper) wire.

My HVAC subcontractor and I actually measured the power draw while the unit was running. It was drawing 14 amps, which is how I arrived at 3400 watts (14 amps times 240 volts =3360 watts) (I rounded up to 3400 watts) By the way, this particular unit uses 4.5 gallons of water per minute whenever it is running, which in my case is about two or three hours per day, usually. You can adjust the water flow rate. Using more water makes the system slightly more efficient, but wastes water and, obviously, increases pumping costs. Using less water than 4.5 gpm. saves water, lowers pumping costs, but decreases efficiency. When I have adjusted the flow rate up to about 7.5 gpm, just to see what happened, the air coming out of my floor register went from about twenty degrees higher than house temp to about twenty five degrees above house temp. (This is a lot higher than my next door neighbor's increase with his "regular" heat pump, which only raises the temp abotut four or five degrees above house temp when outdoor ambient temps are in high thirties, he tells me.)

Rick, I too am amazed that this three ton unit uses only 3400 watts, since this is only slightly more than the use of two portable 110 volt electric heaters. (1500 watts each) In fact, when my wife has asked if she should turn on a portable heater to warm her art studio a few degrees when she hasn't had it heated for a few days, I say, heck no, turn up the heat on the whole house! The heat pump provides four times as much heat per dollar spent than the portable heater!

A couple of other points, for those who may be interested:

There are two basic types of systems available for a geothermal heat pump--closed loop and open loop. Mine is an open loop, as the water is not recirculated. A closed loop either runs water (with food grade antifreeze mixed into it, I THINK) in a loop down into the water in your well, or runs a water/antifreeze solutionn through several hundred feet of pipe buried about (in this area) five feet deep.

The advantage of the open loop system is it is cheaper to install, (tho you may need to drill a return well to avoid depleting the groundwater, if you don't have water running out onto the ground all winter, as I do.) Also the closed loop system remains equally efficient all year, as the groundwater temp remains constant.

A closed loop is somewhat less efficient, because the recirculated water gradually cools off throughout the winter, thus reducing the efficiency until it may even be as low as a "regular" heat pump.

To have a successful open loop system, it is necessary to have fairly good quality groundwater, so as to not have rapid mineral buildup, which is not a consideration in a closed loop system, since the water/ antifreeze solution is made up with high quality water anyway.

I also recommend a copper-nickel heat exchanger for an open loop system. Apparently I may have to "acid wash" my heat exchanger (although I have had no noticeable drop in efficiency after over two years of operation), and the copper-nickel exchanger will take acid washes better without dissolving, or something.

In the summer time, you can only imagine how efficient this unit is, considering it is using 50+ degree water rather than 90+ degree air to dump excess heat from the house into! (I almost wish I hadn't done such a good job designing the house; I've only had to use the air con part of the heat pump maybe ten or fifteen hours so far in over two years)

By the way, on another subject, you can save big $, in low humidity climates (like here in Oregon in the summer) by installing a whole house fan. I can drop the house temp by ten or twenty degrees in as many minutes if I turn on my "attic" fan when I get up at four of five in the morning (54 year old prostate, you know). This is because the dirunal temperature range in this type of climate can be up to about fifty degrees. When I can get the house down to maybe sixty degrees early in the morning, it doesn't really get very hot all day.

-- jumpoff joe (jumpoff@echoweb.net), January 19, 2000.