Geo-Thermal Heat Pumps

[Guest]

http://www.eere.energy.gov/consumerinfo/factsheets/ghp_homeowners.html

On average, a geothermal heat pump system costs about $2,500 per ton of capacity, or roughly $7,500 for a 3-ton unit (typical residential size). In comparison, other systems would cost about $4,000 with air conditioning. When included in the mortgage, the homeowner has a positive cash flow from the beginning. For example, say that the extra $3,500 will add $30 per month to each mortgage payment.

[280plus]

I'd be looking into that energy star loan. Incidenatally, I think their figures are low. The ductwork alone on the house i'm doing is $7000 THEN there's all the equipment, materials (pipe etc) and installation. The GTHP EQUIPMENT might cost what they say but I believe they are leaving out the rest of the job from the figures. There's either a bunch of trenches to dig or multiple wells to drill too. Their figures are skewed horribly or more like misrepresented.

I'm going off now. I'll check back in tomorrow!

[Guest]

What do you think about combining the use of a GTHP with either an earth-bermed or earth-sheltered design and some amount of solar energy usage?

Hi Barbara.    You linked to my "OurCoolHouse.com" website and I followed your link back here.

Tying Geothermal (GSHP) to Radiant heat (and cool) is EXTREMELY practical and not really that expensive (depending on your land etc).

I have geothermal radiant  heat, and geothermal ducted air (heat and cool).   My winter heating bills are a fracton of my neighbors (I live in the mounains of Western MD: 80" of snow on average).

I'm also earth sheltered (rear and side walls) and I also have an Energy Recovery Ventilator.  

And finally, mine is a passive solar design (no solar cells or a anything like that) which uses the nartual winter/summer sun cycles to heat and cool the house.

These things don't automatically make a house expensive, it's just a matter of giving up some other things to ballance the budget (like granite counter tops and 3-4 bathrooms

Phil.

[Guest]

Cold doesn't radiate like heat does, it's much more effective when actually circulated via a fan.

Actually, cold radiates EXACTLY like heat does.  Heat transfer through radiation is dictated by the temperature difference between the two radiating surfaces.  You are one surface and the slab/walls/floor are the other.  Heat always moves from the hot surface to the cold one.

A basement or cave feels cold because the walls are cool.

Radiant cooling can be very effcient, and the only trick to eliminating condensation is to make sure the surface temperature does not get below the dew point of the air.  You can do this by 1) monitoring the humidity, and controling the surface temperature, or 2) Dehumidifying the interior air and thereby raising the dew point.

Circulating the water from a ground loop through some air coils is a great way to pull the moisture out at a central location...  then the same water can be used to cool a radiant slab.  Remeber the slab doesn't have to be "cold" it just needs to be cooler than your body to generate a net heat loss.  

I actually can run my GSHP in reverse and cool my slab.  It only takes a few degrees to make a difference.  Cooling the air and blowing it around the house and hoping it's cool enough by the time it reaches the far side is pretty a indirect way to cool a person.

Phil
www.OurCoolHouse.com

[K Frame]

280,

"I have a little issue with the way they use the DHW heater for the slab. Most towns around here won't let you do that because in the summer that water stagnates in the slab abd then can contaminate your fresh hot water (or DHW) tank and make you ill."

They don't.

"This configuration keeps the domestic hot water separate from the radiant slab fluid, which can then contain an additive to prevent freezing."

National plumbing code won't allow hydronic water to be mixed with domestic hot water. The big concern is Legionaire's Disease.

[K Frame]

Barbara,

That's an AVERAGE cost. Friends looked into this option in the Springfield, Virginia, area, and were quoted costs of roughly $5,000 per ton, and that didn't include all of the excavation work to plant the loops.

Systems using wells are normally a lot more expensive depending on the number of wells you need.

If you have someone quote you a price, make absolutely certain that it includes all excavation and coverage costs, as well.

[K Frame]

"Are you familiar with the term "Cold 70"?"

I assume that you're not talking about the Igloo 70 quart cooler.

I'd really want to see some installation and usage costs on a system such as that.

I can't imagine that it would be any more effective than using a multi-speed system connected to internal and external thermostats and humidistats, but I can imagine it being a lot more expensive.

[K Frame]

"Actually, cold radiates EXACTLY like heat does."

Phil,

I said that poorly.

Cold air stratifies much more readily than heated air, and will produce virtually no convection currents. I supposed the best solution to that would be ceiling mounted cooling panels.

I need to read more about this. I'm still very dubious about the concept as a whole.

I found this link from UBerkley: http://www.cbe.berkeley.edu/research/radiant_cooling.htm

I'll read up on it, but I'm still quite dubious.

[Guest]

Welcome, Phil. I'm on my way to work but wanted to thank you for stopping by..I suspect I'll have a lot more to read on the subject tonight.

I love your house!

[280plus]

"I have a little issue with the way they use the DHW heater for the slab. Most towns around here won't let you do that because in the summer that water stagnates in the slab abd then can contaminate your fresh hot water (or DHW) tank and make you ill."

They don't.

Mike, if you look closely at the diagram of the heat pump setup you will see that it DOES show using the DHW for slab heat. You CAN use a DHW heater but CANNOT or SHOULD NOT connect it to the DHW you'll use for drinking, washing etc.

"cold 70" is a term coined for the phenomenon where the air temp is 70* but all the surrounding surfaces are much colder. Walls, floor, ceiling, furniture etc. Even though a thermometer will indicate the air temp is 70 people feel cold. Best example I can think of is a bank once where they had granite counters and brick walls. They would shut the heat off at night and all that rock in there would achieve something like 56* IIRC. When they turned the heat back on in the A.M. the air would warm to 70* but all the rock would still be 56* even by late afternoon. Those girls were FREEZING even though the air temp was 70*.

Why? Cold does not radiate, heat does. In effect their warm little (some not so little) bodies were radiating their heat to the cold surfaces making them feel chilly. You might look at it as the cold surfaces were pretty much "sucking" the heat out of them.

Anyhow, thats how "radiant cooling" works. As a matter of fact, now that Phil mentions it I DO recall something about cooling the ceiling. Honest, they do it in Germany.

I can't imagine that it would be any more effective than using a multi-speed system connected to internal and external thermostats and humidistats, but I can imagine it being a lot more expensive.

This is MY contention. Yes GTHP are considered to be the most efficient heat around however, I can't buy 40% savings over a well designed high efficiency oil fired system. I too would like to see hard numbers but unles you build 2 identical houses side by side one with GTHP the other with a good oil system and compare the reults it is nearly impossible to verify any of this.

40% over an old furnace, definitely. 40% over a high efficiency oil fired hydronic system? Not likely. Maybe 20% I'd buy.

They say 40%. %40 over WHAT!? They conveniently leave that part out.

Nice system Phil! I may be drooling...

I'm going to correct myself. While the diagram shows the DHW hooked to the slab I don't have enough info there to determine exactly what's going on. From what I am reading the heat pump heats either one or the other. As long as there is no way for slab water to find it's way back into DHW then it's ok. A DHW heater is another accepted way to heat a radiant system due to it's being designed for low water temps and there are those that use them. There WERE also those who were using them simultaneously for DHW. This was found to be a bad idea for the reasons described above.

[cfabe]

280 has touched on what I think is another phenomonen that is worth noting. You will only ever find "advanced" heating systems such as geothermal heat pumps in custom designed houses built by people with a focus on overall heating efficency. These houses almost always will tend to have other features to make heating efficient such as earth-berming, super insulation, very high quality windows, passive solar design, and also have a homeowner who isn't going to run the heat at 75F during the winter. So it's very hard to compare the real-world performance of a GTHP with a "normal" heating system because most "normal" houses are also built with leaky cheap builder windows and shoddily insulated to minimum code, and have homeowners who don't really care other than bitching about their bills.

In theory these systems are the most efficient, but in practice they may not be, espicially if the implementation is not engineered perfectly. In my area (northeast Ohio) there are more than a few houses built in the early to mid 80s using air source heat pumps. Lots of problems with these because of improper system design. In a heat pump system when the heat pump can't keep up with the heating load in the house, electric resistance backup heating is used. For air-source systems, I believe this usually occurs when the outside temp drops below the mid 30s F. So around here the home with air-source heat pumps have nice low bills in the fall and spring, but tremendous bills if january and feb if we get a cold spell. Geothermal does help this by keeping a more constant temperature heat source, but this is just one example of poor implementation. If these guys with air-source pumps had also had a natural gas backup furnace instead of electric, they'd be much better off.

[280plus]

yup, what cfabe said. Same for here in the 80's. They "intelligently" took a very efficient source of heat and coupled it to the worlds worst: electric resistance. With the results he(?) has described. They did start hooking them up to fosiil fuel systems but the heat pump fell out of favor due to the A. cooler discharge air temp and B. the electric heat fiasco. So it never really recovered from that. Nobody around here wants to hear the phrase "Heat Pump".Plus, and this is very important, more than half the "licensed technicians" around here don't have the first ideas on how to repair them properly. An air source heat pump is a VERY efficient means to heat your house down to ~40* Outdoor temp (ODT) but much below that and it frosts over which results in it needing to defrost. In order to do that it turns back into an A/C and turns on the electric heat to compensate for the cool air coming out of it into the house. Totally blows the efficiency rating out the window. So if your climate goes below 40* ODT I like to simply shut them off around 40* and turn to oil. Oil through a high efficiency boiler is the next most efficient of all the ways to heat. It blows natural gas and especially propane out of the water. Even if you're using a 90%+ gas appliance. Oil will still beat it on savings. GTHPs are not subject to the low ambient temps that air source HPs are as the ground supplies a constant 55+* which is more than enough to make a heat pump work and with no defrost cycle.

The reason heat pumps are so efficient is nothing is being burned or consumed to provide the heat. It is simply taking the heat inherently present in the ground (or air), concentrating it (if you will) and transfering it into your house.

[K Frame]

280,

The diagram is, at best, nebulous. I'm going by what they're saying, in words, on the website. As I noted, Nat. Plumbing Code won't allow heating and potable water systems to be linked.

There are water heaters available that have a tank for domestic hot water and a coil that sits in the tank. In that sense, it's no different from a boiler with a domestic hot water coil.

That set up is allowed by the code.

[K Frame]

I have a heat pump in Northern Virginia. It's a Trane, 12.5 SEER (I think). I installed it back in 1996.

Even during the coldest spells, where the temperature doesn't go above freezing during the day, I rarely see my auxilliary heat (the toaster, as I call it) come on.

I used to moan like crazy about a heat pump, because the heat it provides just isn't "warm." However, given the price of gas and oil over the last couple of years, I'm liking my heat pump more and more. I'm not seeing the ENORMOUS spikes in prices that my friends and family are seeing.

Yes, I'd like to have hot water heat, or steam heat (I grew up in a house with steam heat), but I'm comfortable in my house with a heat pump, and spot heating when necessary with a little electric heater.

[mfree]

The easy way not to get sucked into the "cold trap" is to remember this: there is no cold. There is heat, and there is no heat. Where there is heat, it will naturally and gradually make it's way to where there is less heat. Or, you can force it along. You can also gather a lot of little heat and concentrate it (heat pumps).

But there is no cold. Consider it like a vacuum or a darkness, it can't radiate as there's nothing really there.

[280plus]

The diagram is, at best, nebulous.

Yup, the way it appears the slab and DHW look linked but you're right, it could be an indirect water heater and an incorrect  diagram.

12+ SEER means you took "The High Road" when you purchased your system and now you reap the benefits. It get's a bit colder up here in CT though so our "toasters" (I like that one) come on much more often. That defrost is a killer. Does yours develop and hold frost on the outside unit when it's cold?? Another killer is an improperly charged system. If It's undercharged the heat will run much more to keep up and use those toasters even more. If it is overcharged OR undercharged it will not cool well either and, once again, run more often and longer than it should.

A 12+SEER Air Source Heat pump that switches over to a high efficiency oil fired hydro air system at around 40* (maybe a little lower) would provide very comfortable heat and be miserly on the fuel consumption. Now you're not digging trences or drilling wells either.

[280plus]

But there is no cold. Consider it like a vacuum or a darkness, it can't radiate as there's nothing really there.

I like that on too!

It reminds me of another axiom "Light bulbs don't emit light, they suck in dark."

Then there's "Is it the electrons moving forward or the holes where the electrons go moving backward that creates current flow?"

But I digress...

LOL

[K Frame]

Let's face it, folks.

The only thing in this universe that truly radiated cold was my exwife.

She'd open her mouth and the heat pump would come on.

[K Frame]

Any heat pump will develop a frost layer within certain humidity/temperature parameters.

Mine has an "intelligent sensor" on it that detects when ice has built up. It's much better than the old systems that were regulated by a timer.

[280plus]

Any heat pump will develop a frost layer within certain humidity/temperature parameters.

Yes, but if the ODT is far enough above freezing the frost will melt off during the "off" cycle as opposed to needing a defrost.

Mine has an "intelligent sensor" on it that detects when ice has built up. It's much better than the old systems that were regulated by a timer.

Yes, in the "old days" some had a timer that would electrically "ask" the heat pump, by means of a thermostat, every 30 minutes if it wanted a defrost and if the weather was particularly cold or HP was not operating correctly it WOULD go into defrost every 30 minutes and I pity the wallet that's got THAT going on.

Others had a pressure switch that sensed a lowering of air pressure between the condenser fan and coil, indicating that the fan was trying to draw against a blocked coil, and trip it into defrost that way. IIRC there was also a brand that used a sail switch in the airstream. As the ice built up the air velocity over the coil would slow to the point where the sail switch would cycle and initiate a defrost.

Another problem with the "toaster" type HP setup was if the HP failed and the system automatically switched itself over to "emergency heat" people would not know this and would be heating their houses with the toasters instead of HP. This too makes for a big electric bill. This caused some loss of popularity as well

[cfabe]

I believe that some/most of the heat pump systems had an indicator light on the thermostat that would illuminate when they were in "emergency heat" mode. Of course if you never look at the thermostat, that doesn't help much.

In my (future) house I think I'm going to do hot water heat using either in floor or base boards as a baseline heating system that will keep the house at 55-60 and wood heat to supplement. Advantage with hot water is that it's easy for  a layman with a little plumbing experience to install. In my area if a house is designed well there's really only a few weeks a year where a/c is necessary/desired, and I'd just get a window unit for the bedroom if necessary.

[Guest]

Ok, I'm lost..can the HP be backed up with another source of heat?

I would plan on the house having a second source of heat anyway, most likely wood for those chilly nights.

[280plus]

I believe that some/most of the heat pump systems had an indicator light on the thermostat that would illuminate when they were in "emergency heat" mode

yes that's true as long as you physically switch the t'stat to "Emergency heat" if it turns on automatically because the HP is not keeping up MOST will have no indication that you are using the strip heaters. There was at least one that DID give a fault light when things weren't right.

Barb, an  air source HP In Northern climates DOES need supplemental heat as they are unable to keep up once the outside air temp gets too low. Most automatically shift to a secondary source of heat. Worst case is switching it to electric heat. A ground source should not require any additional heat. Air source means it collects heat from the surrounding outside air. Ground source is your Geothermal collecting heat from the ground. A geo thermal is also what we call a water source HP as it picks up heat from a source of water. There are many ways to put heat back into the water once it has been removed by the HP and transfered to the space. In the case of a GTHP the water is reheated by passing it through the relatively warm ground. if you can expect to be without power for 3 weeks a wood stove and a good supply of wood wouldn't be a bad idea at all regardless of what type you have.

[K Frame]

"Yes, but if the ODT is far enough above freezing the frost will melt off during the "off" cycle as opposed to needing a defrost."

??


Here's my original statement: "Any heat pump will develop a frost layer within certain humidity/temperature parameters."

There's no but statement required; my wording makes it abundantly clear that frosting/icing does NOT occur all the time. My unit goes into defrost mode most when the temperature is between about 40 and 45 deg. F and the humidity is in the 50% plus range, which actually occurrs fairly frequently here in DC in the fall.



"I believe that some/most of the heat pump systems had an indicator light on the thermostat that would illuminate when they were in "emergency heat" mode. Of course if you never look at the thermostat, that doesn't help much."

I believe that all thermostats made for use with a heat pump with electric resistance heat have this light.


"Advantage with hot water is that it's easy for  a layman with a little plumbing experience to install."

DANGER WILL ROBINSON! DANGER WILL ROBINSON!

Yes, relatively easy to install, but the big question is, who is going to do your design? That's the kicker part.

I have very fond memories of telling a rather arrogant know it all (who for some really really liked me) that he had REALLY screwed up when trying to save a few bucks doing his own heating renovations.

He decided to pull the old, ugly, outdated cast iron radiators out of his house and replace them with baseboard units. Fairly common thing to do, I personally hate to see it, but I like the old CI radiators.

The only problem was, he replaced the radiators with similar lengths of slant fin. The end result? He reduced the amount of heat going into his rooms by anywhere from 2/3 to 3/4ths. His wife as NOT pleased with him, and he wasn't pleased with me when I told him he screwed up, and then proceeded to explain to him how he screwed up.

His poor ego.

[K Frame]

"yes that's true as long as you physically switch the t'stat to "Emergency heat" if it turns on automatically because the HP is not keeping up MOST will have no indication that you are using the strip heaters."

Incorrect.

At least that's incorrect if the T-stat is properly installed and is designed for use with a heat pump. And given that you need a heat pump thermostat to run the supplemental heat, chances are pretty good that you're going to have the proper T-stat with the little light.

If the emergency coils switch on for any reason, that little light is supposed to go on on the T-stat. That includes the system being switched to emergency, the system dropping into reversing mode to defrost, or the system requiring more heat than can be extracted from the atmosphere (usually a differential of about 1.5 deg. from the T-stat to registered room temp).

My 12 SEER Trane replaced a 6 SEER Rudd that had been installed when the home was built in 1979. The thermostat was original to the unit, as well, and it had the emergency heat light that lit under all conditions noted.

I decided it was time to upgrade when the reversing valve reversed one evening during a defrost and refused to unreverse.