Geothermal heat pump install with crawlspace encapsulation

[Country Geek]

I had started and participated in a thread or two here recently about geothermal heat pumps, trying to decide if one is right for me. I've decided to pull the trigger and I'll follow the install on this thread.

Background: I'm replacing a dual-fuel air-source heat pump. The backup furnace is propane. When I built my house propane was $1 a gallon. Now as we all know it's much more, and also much more volatile. Plus, the local market here is quickly evolving into a duopoly as the two big players (Amerigas and Ferrellgas) are systematically buying up all the mom-n-pops. So I just don't think conditions are favorable for propane heating any more. Last January, during the polar vortex, one month of propane cost me $850. And that's at a significant discount because I had signed a contract in the fall and was getting a commercial rate, plus I own my tank so was also getting a favorable rate for that.

My system is also aging and in need of replacement. The refrigerant it uses is being phased out, and the system is in bad shape because it's located in a crawlspace and 15 years of humidity under there plus critters messing with the ducts has taken its toll. To protect against the latter I'm also having my crawlspace encapsulated, which I'll discuss in another post.

I spent some time deciding on a system type. I first got a quote for a solar-assisted air-source heat pump. This is a regular heat pump system plus solar panels through which refrigerant circulates, making the heat pump more efficient. The research I did made me think this was more a gimmick to make a regular heat pump eligible for energy efficiency credits, than a real efficient system. I settled on geothermal because it's by far the most efficient plus I have the land to do a trench system, reducing cost vs wells.

Cost was a factor and here tax credits are a big help. There is a 30% federal tax credit on a geothermal installation. Plus the state of North Carolina has a 35% credit so in the end that works out to over a 50% discount on the system. I say 50% discount, not the 65% discount that would seem apparent because:

• The state tax reduction also reduces your state income tax deduction on your federal taxes, so for all practical purposes you pay federal income tax on the state tax credit
• The NC credit is capped at $10,500

I did a lot of doodling around in this spreadsheet: http://www.eia.gov/tools/faqs/heatcalc.xls. Putting in local values and playing around, plus the fact that I have the land to do it, a geothermal system looked like a no-brainer.

I'll be putting in a 5 ton ClimateMaster Tranquility with gas backup. It may sound funny to say I'm getting the gas backup after what I said above, but all research I've done shows that geothermal systems around here almost never need backup heat. The gas backup is just for peace of mind because I can run it off my 5500W generator in the event of an extended power outage (which ice storms out here can cause), or if a problem develops with the geothermal system. The gas backup will be manually controlled, not on a thermostat, so I can turn it on and off as I want. I expect to run it very seldom, but who knows, if the price of propane crashes, I could run it more. I will have 7 trenches, 150 feet each.

The trenches will be in my pasture. While the trenches are being installed and the grass regrown, the horse will be living in the training round pen and her stall. It's an inconvenience but she's old and doesn't need a lot of running room any more so she'll be fine.

Once this project starts my pasture will be completely torn up. So I've attached a picture of what it looks like now, because it won't look this good again for a long time! The pasture also has a french drain through it that will need to be avoided by the trenches, it's marked with the orange spray paint. Finally, the horse in her temporary lodging.

 

[Country Geek]

I mentioned in the start post that I will also be doing crawlspace encapsulation.

For decades the conventional wisdom and the building code in the southeast was that you build on a crawlspace with vents that you open in the summer and close in the winter. After a 20+ year study by our state university, that conventional wisdom has been debunked.

The main problem with the conventional wisdom is that in the summer the open vents draw in humid air, which condenses on surfaces in the crawlspace. Especially any HVAC equipment down there! This causes rust and water damage. It also encourages mold and mildew. Because of this, many crawlspaces around here, including mine, are not places you want to go, or to store anything you value that can't be wet (like tools, etc).

Another problem I have in the country is critters. In the winter the raccoons, possums, mice, etc, go under there to stay warm, aided by the fact that the larger critters have pulled off crawlspace vents. These critters then pull down the fiberglass insulation to nest in, damage the ductwork, etc. The ductwork damage is especially a problem because it not only reduces the HVAC effectiveness but it also draws in odors from the crawlspace... which can be bad because of the aformentioned critters, not to mention the mold and mildew.

The answer to this, and the new conventional wisdom down here, is crawlspace encapsulation. Basically the crawlspace becomes part of the conditioned space in the house. All the fiberglass insulation is removed from the subfloor and instead the exterior crawlspace walls are insulated. All vents and openings are sealed up. The floor is completely covered with 20 mil plastic that also goes up the walls and piers to make good, sealed barrier. Two duct openings are made so that the crawlspace is conditioned like the rest of the house, and/or a dehumidifier is added. There may be other steps I'm not remembering right now.

Since I'm having my HVAC redone, I'll do this at the same time. The HVAC contractor will remove the old equipment, the encapsulation contractor will do their thing, then the new HVAC equipment will be added.

There is much more info about this process at: http://crawlspaces.org/

 

[techman]

I would question the cost and complexity of the gas backup. If properly sized, with a geo thermal, you should never need backup. In my home, in colder PA, I have never had the backup heat on, except to test it. Think of it more as "emergency heat". I would save the money and use some of it to buy a bigger generator, so that you can operate the geo system during a power loss. I can easily run my 5 tons worth of heat pumps (2 geo, 1 air) with a 10 KW. I had an 8KW before and it could handle the load as well. You did not mention if you use propane for other needs, but if not I would keep it simple. Another backups to consider is a wood stove. One thing to consider is if you install a gas furnace with a coil on top, the furnace will see dust and moisture, and without some run time to clean and dry the heat exchanger, it could rust out and leave you stranded in some years.

Just my thoughts.

Paul

 

[wngsprd]

Thanks for sharing the crawlspace findings. I've often wondered about these very points.

We also have a Tranquility geothermal unit, and very happy with it. I look forward to your progress reports.

 

[Stimw]

The 3 ton geo that I had was on a 30 amp circuit! It took 23 amps for unit and 7 amps for the water pump.
I measured the temp coming out of a register on heat and the room was 70* and the air coming out was 90*.
They are VERY efficient depending on ground water temp. (my ground water temp 65*)

 

[BobRip]

My crawl space is sealed. The exterior walls are insulated concrete forms (styrofoam inside and out with concrete between). Plasitic on the ground is covered with about one inch of concrete. it works very well. A key point I have an air to air Heat exchanger and I modifed it to put more air in the house than is pulled out. This eliminated some mold smell in the crawl space by providing a slight positive pressure.

 

[whistlepig]

We have a geothermal closed loop with a WaterFurnace. It has the auxiliary heat option. Auxiliary heat rarely kicks in but last winter with wind chills of -30 the auxiliary heat kept of with the temperatures. The closed loop field is under our horse pasture about 50 yards from the house. For backup we use a pellet stove that we can run off a portable generator. We only use the pellet stove for backup heat. We also have the de-superheater option. Just some thoughts. Sounds like you have an excellent plan going. Geothermal is nice.

 

[Country Geek]

Thanks for you feedback. Here are my thoughts on it:

I would question the cost and complexity of the gas backup. If properly sized, with a geo thermal, you should never need backup. In my home, in colder PA, I have never had the backup heat on, except to test it. Think of it more as "emergency heat".

That's how I'm thinking of it. Also my house has high heat loss, with very large windows and high ceilings and the Climatemaster rep who did the calculation figured I might need the aux heat when the outside temp gets down to 20 or so.

I would save the money and use some of it to buy a bigger generator, so that you can operate the geo system during a power loss.

Well my house is already wired with a generator sub panel that is designed to be powered by a 5kw generator. The existing gas furnace is on that panel and the new one will be as well. So a lot of the pieces are already in place.

I can easily run my 5 tons worth of heat pumps (2 geo, 1 air) with a 10 KW.

I did discuss several options with my installer including a split system or type of system where a generator could power the geo heat pump. He was leery if that because of the startup demand from the compressor plus the relatively dirty power from a generator, plus the preponderance of circuit boards in modern units, he thought I would need a soft start kit and some extra voltage regulation to safely run my heat pump with a generator.

Another backups to consider is a wood stove.

I had thought of that because I like the idea. But the cost delta for adding gas backup was less than the installed cost of a wood stove. And a wood stove would take up a lot of space inside for something I might need one or twice a year, not to mention being more work.

One thing to consider is if you install a gas furnace with a coil on top, the furnace will see dust and moisture, and without some run time to clean and dry the heat exchanger, it could rust out and leave you stranded in some years.

Good point. I'll make sure to run the furnace at least a couple of times every winter.

 

[s219]

I would also skip the gas backup. We have a strip heater backup on our Climate Master system (a bit north of you in VA) and the only times I saw it kick on was when the power had been off for about 6 hours and the house got super cold, or briefly in the morning when it was super cold outside and we had turned the temperature down overnight. We have the controller set to automatically kick on the backup heat whenever the incoming air temp is appreciably colder than the set temp (I forget the spread, but it's probably on the order of 10-12 deg F).

I do think it's good to have a backup system, but definitely didn't see the point in springing for a gas system and our HVAC guy said the same thing. Given how rarely the strip heaters kick on, I think that was a good decision.

A side consideration for us was whether or not we really needed propane for anything, and we were able to avoid it all together. I suppose if you already have it, that's a different story. But still, I would really have a hard time springing for the extra cost / complexity of a gas furnace, especially even further south!! Our fireplace can put a big dent in heating requirements when we get it cranking, and I sort of count on that as the real backup.

 

[s219]

I did discuss several options with my installer including a split system or type of system where a generator could power the geo heat pump. He was leery if that because of the startup demand from the compressor plus the relatively dirty power from a generator, plus the preponderance of circuit boards in modern units, he thought I would need a soft start kit and some extra voltage regulation to safely run my heat pump with a generator.

We just put the Climate Master soft-start module on our geo unit today, precisely so that I could run easier on generator power (our particular Climate Master unit has about a 125 amp startup requirement, and it was noticeable even when running off the grid). With the soft-start kit, there isn't even a light flicker anymore. The kit was about $300 if I remember right.