geothermal heating/cooling

He found the unit was unserviceable. Local service people tore up his yard and his floors trying to find the problem, but without success.

So there he was with two extra wells on the property and a lot of subterranian pipe, but he finally deduced that the heat exchanger was leaking freon into the water and junked the whole thing in favour of a wood stove in the basement.

From his experience, an old heat pump is neither pretty nor cheap.

There is a great deal to learn to understand how to do this right. I must have spend several hundred hours over a couple of years learning about heat loads, unit sizing, ductwork design, loop design, etc. Plus my sheetmetal skills got a workout in running all the ductwork. I already owned a backhoe, so the ground loop installation was "free", but it still took a week of digging and 60 gallons of diesel fuel.

Ground loop heat pumps make the most sense in the following circumstances:

1) The heating demand is relatively modest -- the climate is not "severe cold". Say up to about 7000 heating degree days per year.

2) You want or need air conditioning as well as heating.

3) This is new construction, so you have freedom to design the ductwork and supply/return registers for the high air volumes needed for heat pump systems.

4) You have a conditioned basement or a first floor utility room to install the blower/compressor unit.

5) You run the ductwork through the basement or through dropped ceilings, and not through an unconditioned attic.

6) You have a couple of acres of "spare" land to run the loops through. The loops should not be under driveways or garages. The soil WILL settle in the area of the trenches, so plan for this when you landscape your yard. (You can't compact the soil too aggressively over your ground loop when backfilling, for fear of damaging the somewhat fragile polyethylene pipe.)

7) You have a contractor that will work with you. Most distributors will not sell directly to someone "not in the trade". You need someone with the tools and training to do the socket fusion "welding" of the polyethylene pipe to get your loop assembled and leak free.

8) You don't mind the lower register temperatures at the heating vents. Typical heat pumps run lower than human body temp when running maxed out, so the outlet air feels cold, even though it is heating the house just fine. You can improve on this with a two-stage unit, the FHP 4 ton unit that I have gets to about 100 degrees on the low stage, so the air feels at least somewhat warm. I put a lot of thought into supply/return placement, and the "drafts" have not been a problem.

9) You pay at least as much attention to designing the insulation and sealing of the house as you do to the HVAC installation.

10) You plan to live in the house for at least 10 years.

In the right circumstances, the performance of these units can be amazing. The economic payback period (trading the higher capital costs to the lower running costs) will depend on the price of energy over the long term. I'm pleased with the performance of my system so far, though I am still a few thousand dollars "in the hole" compared to the cheapest system I could have installed.

The first thing you need to get use too with any HP is lower register temperatures, about 115�, vs about 125� for gas, oil or electric forced air units.

You would also notice the same difference coming from wood heat to a gas, oil or electrice forced air unit.

Most contractors tend to undersize HP units for heating requirements. If the space now requires 100000btu/hr of heat with gas or oil, then you will also need 100000btu/hr of HP.

Then the second problem comes as now people want to use part of the HP 100000btu/hr to heat water. So now were back to 70000btu/hr HP. However you can add demand controls so when you don't need all the HP btu's for room heating you can divert some heat to water heating.

Next comes the complaint that the HP unit isn't worth a darn as it won't heat my home! Gee I wonder why!

A geothermal HP takes it's heat source from the ground temperature or a ground water source. 8ft in the earth the temperature stays pretty close to 50� year around and doesn't vary much.

A HP is most efficent at 45� for heating and is why geothermal units work so well as long as there not undersized and do not use electric strip heaters for back up heating.

I did a cost study one time for a building with the following results:

Natural gas= $.34/hr
HP (air over coil unit) = $.44
LP heating =$.84/hr
Electric= $2.34/hr
All forced air units with fuel heating cost only and can not be used for other types of buildings. Even tho the study is many moons old, the realtionship hasn't changed too much. The advantage of the HP unit was it also has refrigeration for cooling for the same cost.

T_Bone

Geothermal units are a forced air unit. This simplest explanation on the workings of a geothermal unit is it's an A/C unit. Uses the same principal as a semi refrigeration unit. For cooling (it's both a "furnace" and a A/C in one unit)it runs as a normal A/C unit, but uses the constant ground water temp for heat transfer in the condensor rather than "air" as most of us are used to.

In heating mode, the refrigerant is "reversed", in other words your normal "outdoor coil" becomes the "indoor coil" (evaporater and condenser switches roles) and the "heat" is generated from the compression of the refrigerant.

No heat generation or recapture directly from the ground water source.

I'm in SCMN, have an air to air unit. House is a 100 yr old "farm house" 2 story, 1900sq ft. Minimal (if any) wall insulation. 8" of ceiling insulation (walk in attic unheated) with very poor windows.

From the start of heating season in fall until "dead of winter" and from about Mar 1 until the end of heating season, I have about a $100 heating bill. A/C costs run me about $7-9/month. That's in 90 day temps with dew points in the 60-70 degree range running 20 out of 30 days.

A friend put in a geotherm unit in a similar house and has a propane backup (recomended supplement here in the "north country"). He runs the supplement unit once a year to make sure it runs and functions correctly.

Going from a double wide "trailer house" to this set up, he was at 800-900 gal of propane/month in the winter (dryer, hot water, heat) to about 150-250 gal/yr. That was with 3 teen daughter in the house. The only electric cost "different" is running the circulation pump for the ground water.

To have a complete understanding of the refrigeration process we need to define some rules to follow as it matters to use the correct terminology when designing or servicing heating, ventalating or refrigeration systems.

1) Cold only occurs at minus 460�R or absolute zero. Above that we only have a absence of heat or can be stated as lack of heat. This is very important to understand as it helps in understanding all refrigeration or heating processes.

2) The accepted slang term AC does not mean "cold" as the true meaning stands for "air conditioning", that is to heat, cool, clean, humidifiy or dehumidifiy common air.

3) The second Law of Thermodymanics states:
"heat flows from a higher temperature source to a lower temperature source" This is really important to understand when dealing with refrigeration or heating as one can quickly figure direction of heat transfer at any point in a process.

4) There's several types of common heat exchangers:
a) air to air b) air to liquid
c) liquid to liquid

5) All refrigerants have a direct relationship between temperature and pressure (called it's T & P) that is to say that a refrigerant at 100� may have a pressure of 196psig and at 0� a pressure of 24psig. With knowing the T & P of the refrigerant I would know I'm dealing with refrigerant 22 (R22) using the above numbers.

Example #1:
A simple refrigeration process can be explained as where liquid refrigerant (from the bottom of a condensor) is fed into a small diameter orifice (capillary tube) that runs into a larger tube (evaporator). As the refrigerant enters the evaporator the refrigerant expands into saturated vapor (vaporized fluid) thus dropping pressure thus lowering it's temperature, hence the refrigerating effect has just completed.

Using the above T & P already discussed above, the condensor would have a temperature of 100� and the evaporator would be at 0� thus our evaporator would try to gain heat from it's surrounding area as stated by the 2nd Law of Thermodymanics.

Notice we never talked about the use of a compressor in the above example to obtain the refrigerating effect as only T & P was responsible for the cause of refrigeration effect as explained by the 2nd law of Thermodynamics.

Some refrigerated semi trailers and rail cars use a expendable refrigerant based upon the above example.

A typical outdoor HP uses the same above therory of refrigerating effect. A HP just adds a reversing valve for direction of refrigerant flow and a compressor for reusing the refrigerant with-in a closed loop refrigerant system. 0n a typical HP we want to use the evaporator as a condensor sometimes and the condensor as a evaporator sometimes and a reversing valve accomplishs this. The compressor pumps refrigerant from the evaporator to the condensor.

To keep this short as possible we will not address Latent heat of compression, the effect that a compressor adds to the refrigeration cycle.

Notice we never mention using any fans for the above HP unit to complete it's refrigeration cycle nor to obtain the refrigerating effect. Depending on the desired results would we add a fan.

During the time that our outdoor HP is in the heating mode, the condensor is used as a evaporator. That means were trying to refrigerate the ambient air and thus obtain heat, (see the begining of example #1). As the HP continues to run the outside eveporator begins to ice from trying to absorb heat from the surrounding air as well gathers moisture. To defrost this ice build up we momentary reverse the refrigerant flow thus melting the ice and the "swoosh" sound our HP makes when it reverses refrigerant flow.

Now to increase the heat flow to our HP evaporator during heating mode we can add a liquid to liquid heat exchanger with taking heat from a ground source hence the name geothermal. Now that ground source heat could be obtained form well water or a secondary coil located with-in water with a ground source heat sink.

There's many different ways to accomplish a ground source heat gain but a liquid to liquid heat exchanger has the highest efficiency ratio.

T_Bone

My apologies, my post wasn't an attempt to discredit the information within your post.

For lack of a better place to post within the thread, I tacked it onto your's. I just wanted to get an explanation in simple language that most lay people might understand. It's a problem/situation I run into very very often when mentioned that heat pumps don't work in the "north country". Misinformation given out by those not in the know. You know how it is sometimes, if someone doesn't have a clue, they aren't going to make themselves look ignorant and say I don't know. They are going to give a story to boost themselves up.

Your information on any post is completely well thought out and can be backed up without effort should someone question it. Because you have researched prior to posting it. Never did I have a reason to try to discredit it. Again my apologies for giving that impression.
Bruce

LMAO, That thought never entered my mind but now that I reread the two posts it sure could have been taken that way. Boy without body language words sure can take on a different meaning :-)

I go into the teaching mode sometimes without any pre-thought as thats part of what I did when I was working, either with students or with other engineers not fimular with the whole picture of a refrigeration problem, so I took your post as a refrigeration problem that I needed to solve while talking with another engineer.

My mind set is to break down any problem to it's simplest form, so I tend type and talk the same way that I resolve problems in my head or in this case discussing refrigeration theory in block form.

That tends to make me supply to much information to a simple question or problem. I also don't get alot of feed back on this forum, for whatever reason, so sometimes it hard for me to judge just how much info I should include in my posts to relay my thoughts. Anotherwords am I boring people to death or am I helping or just confusing the issue.

T_Bone

But then, I have a BS in ag with attention to ruminant nutrition and genetics (I aced the ACT math part, hit a 49 on the English...LOL). I have also taken a few courses at the local tech school in HVAC. Have been a fully licensed insurance agent both health/life and property. Add all the normal experiences/knowledge that comes being involved in the farm for over 40 yrs, I can look at a picture and duplicate an item suited to my particular needs without a blueprint. But I will be the first to admit I'm a master of none of the above.

I'm not saying your posts are any of what you listed. Some of us read them like the daily paper, and I'm sure others read it like it was the Hebrew Bible. Just the nature of the dog dealing with such a wide spread base of people. You just can't please everyone.

Don't change your style on my account, you post just fine for myself.