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Geothermal back-up question

Posted by mariaswell (My Page) on
Sat, Mar 8, 14 at 20:45

I'm buying a house that has a 3 coil geothermal system with a heat pump. I don't even know what that means, I'm currently researching it to get a little more knowledgeable about the system in general, so please bear with me.

My question is about back-up heating that I've read about in several posts. Does this mean an entirely separate system, or merely a backup energy source? I'm having a 20kw diesel generator installed, does that satisfy the backup needs of a geothermal system? I live in a cold climate, I want to make sure I'm covered.


Follow-Up Postings:

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RE: Geothermal back-up question

“I'm buying a house that has a 3 coil geothermal system with a heat pump. I don't even know what that means”.

I don’t either; you’re not making any sense. Let’s start with you posting the make & model of each heat pump and whatever details you have on this system, particularly the ground loops. Where is this house?

What documentation has the original owner provided you with about this system?

Post back.

SR


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RE: Geothermal back-up question

Thanks for responding! The only documentation I have on this system so far is what's detailed in the sellers disclosure, which states the geothermal system itself was installed in 1998 and a new heat pump in June of last year. I've included a link for the model I have below. It states only ground loop, not whether it's open or closed loop (see I'm learning!). I live in northern missouri, where it gets pretty darn cold.

Here is a link that might be useful: Heat pump

This post was edited by mariaswell on Sun, Mar 9, 14 at 1:43


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RE: Geothermal back-up question

The reference to "3 coil" may be the number of well bores or ground loops.

MariasWell,

The geothermal and heat pump aspects of your system go together. Geothermal means the heat pump extracts heat (for heating) from the ground (earth and/or water) instead of from the outside air. it also injects heat (extracted from inside the house) into the ground when in cooling mode.

The benefit of this is that the ground is at a much more stable temperature year-round than is the ambient air.

Back-up does not refer to an accessory power generator (diesel or other). It refers to an alternate heat source.

Non-geothermal (air-source) heat pumps typically include a standard furnace (electric heat strips or natural gas) as the back-up.

This is necessary for air-source heat pumps for three reasons:
1) In case of compressor failure.
2) During defrost (the heat pump switches into air conditioning mode for a few minutes), the back-up heat source activates to warm the cold (air conditioned) air that would otherwise be blowing in the house.
3) At low outdoor temps (35°F or less, typically) air-source heat pumps may not be able to extract enough heat from the outdoor air to keep up with the required heating load, so the back-up activates (if/when the indoor thermostat calls for it) to supplement the heat pump's capacity.

Geothermal systems are MUCH less affected by outdoor air temperature being that they extract heat from the ground, not from the outside air ... so back-up for supplemental purposes is rarely needed. They also don't need to defrost. So that leaves the primary reason for back-up being as an alternate heat source in case of compressor or water circulation pump failure.

My neighbor had a ground-source (closed loop) heat pump installed a few years ago. His system has an electric furnace as the back-up but the heating elements are in fact disconnected (that would be done in the event of a heat pump compressor or circulation pump failure).


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RE: Geothermal back-up question

I would be concerned why a 15 year old geothermal heat pump had to be replaced and not repaired by the current owners. The premature failure could have been caused by a poor installation.

I recommend you hire a geothermal HVAC contractor to do a thorough evaluation of the system and the ground loops before you buy the house.


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RE: Geothermal back-up question

Do you have a pond on the property? "Coil" could mean pond loops - or if horizontal trenching, could be "slinky" loops. You should get specifics on the geothermal system from the current owner, including location (you don't want to find as you're excavating for new inground pool that you've got horizontal ground loops there!). Same with the heat pump - it may have heat strips used for Auxiliary/Emergency heat already installed. Ask the owner to walk you and/or your home inspector (who can then show you) through the operation of the system, including locations of breakers.

We have a GSHP with 10kW and 15kW heat strips installed, we generally keep them turned off 9 months of the year and they very rarely come on (that I see anyway) unless it's consistently below freezing - our electric bill takes a jump when average temperature for the month is 27 degrees or less (meaning nights below zero and highs below freezing all month). I don't know if your location gets as cold as it does here, but this winter has been one to test the system. Even then, I set my Aux Heat lockout (ask owner how to do that on your system, he should still have manual from new HP installation, hopefully that includes thermostat manual) to 25 and this past month the electricity usage was 74.66 kWh/day (whole house, not just heat) when average temp was 22.9, vs 75.10 kWh/day last Feb when avg temp was 27.5. We keep the heat at 67. HTH


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RE: Geothermal back-up question

Dadoes thank you for explaining things in such a clear, concise manner. I do believe I'm starting to "get it". I think the ground source air must also explain the lack of any dust whatsoever in that house. When I toured the property it had been closed up for about 9 weeks, and I was really struck by the fact that there was no dust on baseboards, ceiling fans, furniture, absolutely anywhere in that 3500 sq ft house. I'm sure good insulation accounts for a lot of it too, but I have good insulation in my present home and I have to dust and vacuum regularly.

Mike-home thank you for bringing that to my attention. The owner of the local hvac company that installed the new Carrier goes to my church, and I had the opportunity today to ask him why he replaced it. He told me that there was really nothing wrong with the old one, but that the current owner felt the newer units were much quieter than the one she had installed back in 1998. He didn't do the original install, but he has done all the maintenance on her system and told me she was meticulous in its upkeep.

Ajsmama my heart jumped a little in my chest when I read your post. The reason I am buying this house is for its incredible lot of 9 acres for a POOL I'm going to have built. It is a contingency of my offer that I have to get a pool contractor to approve a site on the property or no sale. He will be out on Wednesday, so we'll see. It does have a pond, and a septic tank, and the way the house is situated on the lot leaves only two areas where I'd like the pool to go. Theres a very nice flat area about a hundred feet from the house and to the right of the pond, and ideally that's where I'd like it built. I'm hoping that's not where the coils are. I'm waiting for the real estate agent to call me back, keeping my fingers crossed.

After all of that, I now know that in fact I do need a backup heat source, not just the generator I want to have installed. I completely forgot to ask the hvac guy about the backup system, but I will find out later today when I speak to the real estate agent. it gets very cold here in northern missouri, even so this winter was one for the record books. The kids had a few snow days off from school, as usual, but this year we also had many days where school was cancelled due to wind chill factors of -30. I'll have the geothermal system, I'll have the backup heat source, the generator for when we lose power at least once a year, and just to be sure, I might even install a wood stove, lol.


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RE: Geothermal back-up question

" I think the ground source air must also explain the lack of any dust whatsoever in that house."

Not sure I understand this statement... the air source heat pump transfers the heat via refrigerant lines between the indoors and outdoors. There is no exchange of dusty outside air and the inside of your house due to the air heat pumps operation.


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RE: Geothermal back-up question

Saltidawg, that was exactly my point, I just phrased it badly. I was impressed that a house that had been closed for a good while was completely dust free, and had an a-ha! moment of realizing it was due to the geothermal system, versus a regular furnace that pulls in air from the outside, creating dust. I hope I explained that right, I have no knowledge of hvac at all.


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RE: Geothermal back-up question

mariaswell,

My comment was based on comparing your geothermal to a heat pump... not to a furnace.

My bad.


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RE: Geothermal back-up question

Definitely find out about current aux/emergency heat (they must have something!), and location of loops - before Wed. Does the current owner, or perhaps town hall building dept, have any site plans/as-builts from when the geothermal was installed? You don't want to rely on the installer's memory from 15 years ago (if that was even the original installer who replaced the HP).

Depending on what else you plan on putting on the generator, 20kW should be able to run the GSHP and/or backup heat, hot water, well pump, kitchen. That's a big generator - automatic switchover? The only whole-house generators I've seen are propane or natural-gas. Of course you must have a huge diesel (home heating oil?) tank to run that.


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RE: Geothermal back-up question

Mariaswell,

With *very few* exceptions, home heating and cooling systems do not pull in air from outside, cool or warm it and blow into the house.

The blower unit inside the house recirculates the air in the house ... pulling it through a filter, then through the cooling coils (evaporator), or across electric heating elements, or through a heat exchanger on a gas furnace, then it blows into a distribution plenum, through the ducts and back into the rooms.

Some commercial systems do have a fresh air intake -- shopping malls, department stores, movie theaters, public auditoriums, etc. -- to provide fresh air to a large assembly of people, but that's different than home systems.

A heat pump is basically an air conditioner that can operate in "reverse" to provide heating instead of cooling.
-- Cooling mode (air conditioner OR heat pump): Heat is moved from inside the house to outside -- the ducts in the house blow cold air, the compressor unit outside blows hot air.
-- Heating mode (heat pump): Heat is moved from outside the house to inside -- the compressor unit outside blows cold air and the ducts in the house blow warm air. Think of it as air conditioning the outdoors.

An air-source heat pump picks up heat from the outside air (heating mode) ... or dumps the heat to the outside air (cooling mode).

A ground-source heat pump picks up heat (through refrigeration, Freon lines, same as a regular system) from the ground/earth or a water source/pond (heating mode) ... or dumps the heat to there (cooling mode).

Remember from physics, there's heat in mass/material (water, earth, air, etc.) down to absolute zero when molecular motion stops.


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RE: Geothermal back-up question

A lot of GREAT posts here. I think mike_home nailed it. I too am still suspicious that a HP was replaced only half way through its life cycle. Only a ‘nut’ does that or there’s something wrong. If the original HP was from 1998, then there’s a good chance it had a reciprocating compressor. I would choose that over a scroll compressor with regard to noise any day, especially since it’s located inside the house.

I would highly recommend getting a third party to independently inspect that system and at least verifying in detail its ‘COP’ - in writing, signed on a company letterhead. A serious attempt has to be made to locate the ground loops.

Buying a home with a geothermal system is a big plus. Not having all the details is a BIG minus!

IMPO

SR


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RE: Geothermal back-up question

Okay, You've all convinced me, I have a company coming from the city on Friday to inspect the system. I met with the realtor today and the owner was kind enough to let us rifle through her personal paperwork in search of the documentation on the system. I will say she is a meticulous records keeper, she has records for absolutely everything ever done to that property from building it in 1972 to the present. Kind of nice to have all that info.

The realtor asked her why she replaced the heat pump and she said because it was so much louder than the pump she has since had installed. She has been an ambassador of sorts for geothermal in this area, she had it installed in 1998, and since then people have come to her house to see, as she puts it, what all this geothermal nonsense is about. She was invited to see a neighbors new system and liked it. Perhaps as fsq4w puts it, she's just a nut.

She also had a whole house humidifier and an air purifier put in at the same time as the new heat pump, and it also generates hot water, which I didn't know previously.

The original heat pump is still in the basement, as well as the new one AND a backup electric furnace, as well as a 50 gal water heater that ties into the system AND a backup electric water heater. So my original question has been answered, I'll have a backup heat source. She also has two portable generators to run them in the event of a power outage, however I will be installing my own generator. I never bothered to look in here previously because I know nothing about any of it, and I was waiting on the home inspectors report to see if there was anything to worry about.

I will have all the reports from all the various inspectors/contractors by Friday, so we'll see what we see. But I feel pretty good about it all.


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RE: Geothermal back-up question

But where are the loops?


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RE: Geothermal back-up question

Ajsmama they are in the pond, pictured above in a previous post. The picture from this post shows the back of the house from right about where I'd like to place the pool perhaps just a bit further out. There's a good acre from the pond to the pool site, and short of hitting bedrock (highly unlikely) there's no impediment to building the pool there.

I meant to answer your previous post regarding the generator. I've decided to wait until the pool is installed and seeing if I'm going to heat it, and how I'm going to heat it, as well as remodeling the inside of the house before I commit to a specific size generator. When everything is complete Ill have an audit done to see what I need. It will have an automatic transfer switch, and I wanted diesel specifically because of its lower flammability and, to me at least, it's fairly easy to store. Coincidentally, the tractor that conveys with the house runs on diesel and there is a fifty gallon tank on site. I also have two portable 20 gallon tanks that allow me to refill at a gas station, so I think I'm covered for diesel.


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RE: Geothermal back-up question

A question I had was how did the original owner know that the replacement HP was going to be quieter? If she visited a neighbor’s installation and heard a big difference, then she may not be a total nut, in fact depending on the noise of her original unit, she may not be a ‘nut’ at all. She may just be, as am I, a ‘Geothermal Evangelist’.

The exact model number of the HP, indicating its capacity, was never posted. It should be marked on the HP. Might you have any further details of the pond loop or even the pond itself, such as size & depth, at this time?

I too like diesel generators.

IMO

SR


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RE: Geothermal back-up question

Home heating oil is cheaper - and I think (someone please correct me if I'm wrong), if you have a tank onsite, connected to autoswitchover generator, you would legally be allowed to get that tank filled by HHO delivery service (if one would come out once a year as needed) and not have to haul diesel in 20 gal tanks from gas station. I assume you have a pump to get the fuel out of the tanks?

Glad the loops won't interfere with the pool installation - you did check for where they were trenched to come into the house (should be easy to see the penetrations in the basement)?


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RE: Geothermal back-up question

A Geothermal Evangelist? I like it, I may convert into one myself. And you're right, she's not a nut at all, she just likes her comfort. The Hp is a Carrier GT-PX 50YDV, it's either a 5 or a 6 ton. The only info I have on the pond is that it's "a half acre pond with galvanized dock, stocked with catfish". I'll have to find out its capacity.

Ajsmama Mfa oil services that property for both diesel and a small propane tank. The 20 gal portable tanks are just backup for a worst case scenario, I'd have the means to get it myself if it couldn't be delivered. I may have to get a bigger tank as the 20kw generator uses about 50 gal in 24 hours at half load. If there was an extended power outage I'd be out of fuel in 48 hours. Something else to think about!

Now that I know where everything is I can clearly see the path the loops take from the pond to the house, in the picture I posted of the pond. It's the flattened area that leads right under the deck, which is where the entrance is to the walk out basement.


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RE: Geothermal back-up question

mariaswell,

As long as we're spending your money.

I watched Richard on This Old House TV connect up a system which allowed the heat removed from the house during cooling season to be diverted from the pond loops to the pool loops.

Thus you get to heat the pool, or contribute to heating the pool, during the summer. While the cost would not be free, the heat is after all waste heat and is sorta "free". (After paying for the installation.

In the version showed on TV, with a throw of a valve or more likely two you were back to the original heat pump arrangement.

IIRC, the unit installed uses a heat exchanger to transfer the heat from the freon to the pool water... in your case, presumably the transfer would be from the fluid in your system to the pool water.

Here is a link that might be useful: TOH Episode

This post was edited by saltidawg on Tue, Mar 11, 14 at 10:31


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RE: Geothermal back-up question

Saltydawg that is ingenious! I'll talk to the inspector about it on Friday when he comes out, maybe I can get a ballpark estimate on it. Thank you!


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RE: Geothermal back-up question

I hope you guys are still checking this thread, I discovered today that the three bedrooms built over the garage are not connected to the geothermal system. At least that's what I think. Help me out here, please.

I'll start at the beginning. When I first toured the house it was very nice and toasty, verging on too warm, until I got to the door that opens into the wing built over the garage that consists of three bedrooms. It wasn't just noticeably cooler, it was very cold. The realtor said the owner kept that part of the house closed off and didn't need to heat it since there was no plumbing in that wing. Sounded good to me.

Fsq4cw asked me a question earlier about the pond and the furnace and I had to look at the sellers disclosure to answer his question, and as I'm looking for what's stated for the pond I see right underneath the description of the geothermal system, it says "2 window ac units, 3 bedrooms over garage electric heat in ceiling". Nowhere does it clearly state the bedrooms are not connected to the system, but why else would those three rooms need both air conditioners and seperate heaters?

I've seen the electric bills for the past few years on this house, they are very low. I assumed mine would probably double as I have children and she is a single woman. But her electric bills don't include heating and cooling those three rooms, so the heating and cooling of those three rooms cancels out the savings of the geothermal system, doesn't it? Tell me I'm wrong, please.

And what in the world is electric ceiling heat anyway? Is there a reason it's not and/or can't be connected to the heat pump? I know you're going to want specifics on the ac and heating units in those rooms, which I don't have yet. I'll post when I do, but in case you need to know, the house was built in 1972, the geothermal installed in 1998, and the garage was built in 2003. The garage is 35x26 and connects to the main level of the house through a 16x6 covered breezeway, the bedrooms are built over the garage an breezeway and connect directly to an exterior wall. You can see in the picture the lower roofline is the garage with windows from two of the bedrooms.

I sure hope I'm making a mountain out of a molehill, and I hope too there's a way to connect those rooms to the heat pump. I really appreciate you guys taking the time to answer my stupid questions and your patience in educating me about all of this.


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RE: Geothermal back-up question

Why did a single woman add bedrooms over the garage? Does she have summer house guests? Seems strange that she wouldn't have connected those rooms to the HP when she built, since the garage was brand new.

Anyway, you really need to get specifics on the pond loops, the new HP (6 ton sounds big enough to add those rooms, but I don't know how big the house is - does the 3500sf include those rooms or not?), and the zoning. You need a Manual J calculation done on the whole house, including those rooms. Maybe they're not well-insulated? A blower door test before the calculations would be helpful. If the current system isn't oversized and can't handle the extra rooms, and the old HP is still there, you *may* be able to reconnect that and use that for the new wing, though that may be overkill since I assume it's 4-5 tons. And you may have to add new loops. Definitely will have to put in ductwork.

I don't know about electric heat in ceiling - seems a weird place to put it, radiant heat in the floors would have been better - even electric baseboards, I'd think.

This post was edited by ajsmama on Wed, Mar 12, 14 at 8:29


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RE: Geothermal back-up question

  • Posted by fsq4cw Mtl/Qc/Can (My Page) on
    Wed, Mar 12, 14 at 20:00

Regarding heating a pool with the existing HP, I wouldn’t get too creative as the existing HP may already have a ‘desuperheater’ that is already using that technique to heat domestic hot water.

The ‘electric heat in ceiling’ requires some clarification. Is it in the ceiling of the garage or the ceiling of the level above the garage?

“… So the heating and cooling of those three rooms cancels out the savings of the geothermal system, doesn't it? Tell me I'm wrong, please.”

Your efficiency going forward will depend on how you choose to space condition this area. One thing is for sure; you cannot use a forced air HP, as you now have, to heat the garage. It would be against code, as carbon monoxide from a motor vehicle could find its way back into the house through a forced air duct in the garage. So that’s out.

Your best option for energy efficiency and flexibility might be to install another geothermal liquid-to-water HP or a ‘triple function’ (forced air heating & cooling, full capacity hot water for hydronic heating of house or pool and Domestic Hot & Water DHW) geothermal heat pump. This way you can heat the garage hydronically, the house (heating & cooling) either hydronically or with forced air, depending which configuration is chosen and heat the pool as well, as Salti eluded to, at ultra high efficiency.

This all would be dependant on the total capacity of your pond. If the existing runouts from the pond were installed in a buried conduit there may be sufficient room to run an additional set of runouts for another HP without having to excavate, which would be a BIG savings in time, money and re-landscaping.

Regarding the size of the current HP just post the model number listed on the spec plate.

SR


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RE: Geothermal back-up question

Can't they run closed ducts (given a chase, that is, maybe coming from attic if the upstairs of main house has ductwork up there) from the finished part of the house to the bedrooms over the garage? I don't think anyone wants to heat a garage - definitely don't want a return there. Or is there a concern that even if the ducts are sealed and supply/return is in insulated space above the garage, that CO can enter the ducts? In that case I'd be worried even sleeping in those rooms right now!


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RE: Geothermal back-up question

Re: ajsmama

I guess it depends where you live that determines if you would want to heat your garage, particularly if it’s within the envelope of the building. What you’ve suggested would be OK. You just cannot have ANY ductwork in a garage in new construction or additions that’s part of the ‘central’ system for obvious reasons. Any negative pressure could circulate CO throughout the home killing, making the occupants sick or just reducing the IAQ.

It is usually ‘permitted’ in retrofits.

SR


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RE: Geothermal back-up question

I think Maria just wants to heat and cool those bedrooms more efficiently than they are now - suspecting that they were so cold during the showings b/c owner doesn't want to get a big electricity bill (Maria, you should request copies of at least the past year's worth of bills).

Cost to retrofit really depends on whether the current ductwork can easily be extended into that upper story (preferrably w/o going though garage) and whether the newer HP and the pond loops can handle the load, or if maybe the older HP still in place can be connected to pond loops. As you said, conduit would make it easier to add pond loops, excavation is possible but risk of damaging existing lines is there and I don't know if there would be a new location suitable for bringing them into the basement.


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RE: Geothermal back-up question

The house inspector was out yesterday and confirmed there is no ductwork in those rooms, and says the electric heaters installed in the ceiling did very little to warm the room an hour later. They are insufficient sources of heat.

This really is just the last straw for me, it has been a bit of a circus trying to get specifics regarding the geothermal system, the septic tank, the well and on and on. The sellers disclosure was all so vague that you really had to read between the lines to know what was actually being said. Both the owner and the realtor had several opportunities to tell me about the rooms in the garage and never did. It feels dishonest to me.

I retracted my offer yesterday. The house needs to be completely remodeled inside, it's been well maintained but it's a time warp back to the 70's. The pool, the generator, a large tractor mower to mow 9 acres, all adds up to a small fortune. I'm not paying a premium for a house with a geothermal system if it doesn't heat and cool the entire house. Im not paying for a five bedroom house if three of those rooms are uninhabitable.

The realtor left me several messages yesterday, so I know the owner is willing to negotiate. Fsq4cw that setup you've outlined sounds like the perfect solution to me and I'm going to have the owner pay to have that estimated. Tomorrow, maybe. Today I feel like being every bit as vague as they've been to me.

I had my very first Freudian slip yesterday. As the inspector and I were about to enter the house I turned to him and said "let's take off our pants so we don't soil the carpet". I MEANT SHOES!!! Dang it.


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RE: Geothermal back-up question

  • Posted by fsq4cw Mtl/Qc/Can (My Page) on
    Thu, Mar 13, 14 at 11:13

Re: ajsmama

If Maria only wants to heat & air-condition the rooms above the garage her best bet might be to just create a separate, zoned ductwork for this space that would be up to code.

Another possibility for expanding the pond loop, if necessary, might be if the pond is big enough and if the runouts are of a large enough diameter to handle the new increased flow and if the headers are buried near the pond, to add more loops to the pond, dig up the headers (near the pond), modify or replace the heads and use the same runouts back to the house without ANY further excavating, re-landscaping or foundation penetrations.

It’s ALWAYS vital to have an ‘As Built’ journal for every geothermal system that details ground/pond loop location, pipe/header sizes/location, HDPE runouts marked their entire length with metalized tape to facilitate future detection with an electronic metal detector, pressure testing measurements of ground loops and procedures BEFORE the ground is closed up, startup procedures and measurement, pictures & diagrams, signatures of the professionals documenting/verifying everything that was done and guaranteeing the delivery of a properly functioning and efficient system meeting that criteria of the day - dated and duly signed.

One copy should remain with the system, one copy for the owner and one copy to be retained by owner in another ‘safe place’, perhaps off site it case of a fire. The installer should retain another copy as well. Both paper and digital copies of all this material should exist in all four places.

Mistakes are VERY serious, inconvenient and costly! I know of at least one case (NOT my wife & I nor MY client!) that resulted in divorce - that’s 2-gargantuan legal battles, one with the contractors and one between the spouses!

Can you imagine?

IMPO

SR


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RE: Geothermal back-up question

Run Run Run

Vague disclosures and less than forthright information in the case of a possible home sale/purchase are indeed dishonest. In some jurisdictions, such actions can lead to the seller paying for remediation with severe consequences

You've stumbled into a couple of problems they were trying to whitewash you about. What else is there you don't know or haven't asked about?

I wouldn't give the place a second thought, and I would communicate your feelings to the two agents. They can have liability too.


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RE: Geothermal back-up question

So wondering how it all went?


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