Geothermal heat pump install with crawlspace encapsulation

[techman]

It's silly.

With no disrespect, it is not silly, it is thermodynamics and math.

Your area has an average ground temp of 50 deg. At 10' depth, there is a +/- 10 deg seasonal variation which would mean that you would see 45 deg at the loop without pulling any heat during winter. Now assume something like 25,000 BTUs average demand in the winter, for typical soils you would see 25000/600 feet* 5 loops is another 8 deg colder. This will bring you down to 37 deg in the winter with a single linear pipe. If the pipe density is higher, as in a slinky, you can have 2 or three times temperature differential, bringing you into the mid 20's or lower. Factors that mitigate that are soil types, or as you stated moisture.

Slinkies are preferred due to a smaller overall area is required and/or reduced digging time and cost.



Paul

 

[V1Rotate]

I know that wells are more expensive than trenches but wouldn't they be more efficient?
If your well went down a couple of hundred feet, you would almost certainly have water running by your pipes carrying heat away.

 

[techman]

I know that wells are more expensive than trenches but wouldn't they be more efficient?
If your well went down a couple of hundred feet, you would almost certainly have water running by your pipes carrying heat away.

Yes. Wells are generally more efficient due to moisture. You can have a dry well, which would have less efficiency, but still benefits from being deep enough to not have any seasonal influences. In that case you still have the "heat flow" issue which will cause temp variations around the drill hole. If you have a moist, or even better a well in water, than the efficiency can be quite a bit higher. Moist or barely wet can also experience ground freezing around the well hole when under high demand. The most common reason for bore holes is available land area. Smaller lots usually require drilling. the down side is that drilling will cost many times what a trench system would cost.

Paul

 

[cre10]

With no disrespect, it is not silly, it is thermodynamics and math.

Your area has an average ground temp of 50 deg. At 10' depth, there is a +/- 10 deg seasonal variation which would mean that you would see 45 deg at the loop without pulling any heat during winter. Now assume something like 25,000 BTUs average demand in the winter, for typical soils you would see 25000/600 feet* 5 loops is another 8 deg colder. This will bring you down to 37 deg in the winter with a single linear pipe. If the pipe density is higher, as in a slinky, you can have 2 or three times temperature differential, bringing you into the mid 20's or lower. Factors that mitigate that are soil types, or as you stated moisture.

Slinkies are preferred due to a smaller overall area is required and/or reduced digging time and cost.

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Paul

With all due respect please read my entire post. It's silly to move that much dirt for a 2 or 4 pipe system. The same could have been accomplished using a small bucket or trencher or using 5-6 slinkies. It could have saved the homeowner $2000 and had the same water temperatures.

 

[cre10]

I know that wells are more expensive than trenches but wouldn't they be more efficient?
If your well went down a couple of hundred feet, you would almost certainly have water running by your pipes carrying heat away.

Wells are good when you have rock, sandy dry soil, steep river bluffs or not enough space. Wells might be more "efficient" using 1200 feet of pipe on a 3 ton system at $6,000, but you can obtain the same water temperatures using more pipe with trenching, slinkies, or pond loops for $3,000. To me water temps being equal, "efficiency" is what costs the homeowner the least amount of money, but performs. For horizontal you don't gain a whole lot unless you go below 25 feet.

 

[cre10]

It is interesting to read about contact area of the geo field pipes. Contact area is nearly the same in any configuration. The big variable is the amount of area between pipes. The heat flow through soil is relatively poor. For most soils it is about 1 deg F/foot/BTU. If pipes are closer together, like in a slinky, the soil around the pipes will chill (or heat) more due to the pipe density and given heat flow. This results in a lower overall efficiency due to the chilling of the soil. One or two pipes in a trench, with trenches 8' apart is ideal, but impractical in some installations. It is documented, and I have also seen up to 20 deg swing in the trench (pipe) temps over seasonal changes. Some of that is ground/depth effects and the rest is low heat flow. My system reaches its lowest efficiency around march, when the incoming water temps are in the upper 20's. Last year was interesting as we had a good layer of snow from December onwards. The snow provided some insulation from the surface temps, and even though it was a much colder winter than usual, the incoming water temps were about 5 deg F warmer than other winters.

paul

Water temps in the 20's is pretty low isn't? What did you take into account when sizing your loop field and units for your home? What anti-freeze and percentage are you running? Most loops here are around 37 degrees at their lowest temperatures, but the poorly designed undersized ones can get much lower or very hot in the summers.

Loop design is extremely important and will save you the most money for operating efficiencies. Just round figures say if you have a 5 ton unit at 32 degree entering water temperature you will get around 49,000 BTU's of output. If that water temp is 50 degrees then you're looking at 64,000 BTU's of output running on 2nd stage. It is equally as dramatic for EER ratings too.

 

[MacLawn]

We have reversible Waterfurnace geothermal with floor heating and high pressure fan coil for AC installed since 2004. We have two propane fireplaces as heat backup and sometime for ambiance. So far our geo works very well but if I build our house today I would use mini-split units and I would invest saved money in PV panels and there would be money left to buy a tractor stuff. The modern mini splits are very quiet inside and outside as well, phenomenally efficient, easy and fast to install and replace, they are way cheaper than Geo and you get a zone for every room in the house and redundant sources of heat and AC as well. We have one in my shop office and one in a guest room for about two years. They are Fujitsu Halcyon but there are other brands that are as good or perhaps even better. Another advantage is that you can get by with much smaller generator because all modern one have "soft" start and you can turn some completely off during outage while maintaining comfort in at least in some areas.

Wow, red, I wouldn't have thought that! We lived in Japan about 30 years using those so called mini split systems, so I know them well. A huge problem with them is you need one for every room! Or at least one outside unit that can handle maybe 2-3 inside wall mount units. We never used that kind in Japan. We had five in our last house in Japan. At $1,000-$2,000 or so per unit, and our house here would need at least 8 inside units, I don't see how they could be cheaper than geothermal. Our house is small, only about 1,500 square feet now, but duct vents even in walk in closet! Could not do that with Japanese heat pumps (that's what we call them there, just heat pumps).

 

[Loadstar]

I would not trade my antique janitrol condensing unit for installed free mini splits.

 

[s219]

Geo systems in my area are almost all done with wells. Our system has 4 wells drilled 15-20 feet apart, each going down about 150 ft and grouted with bentonite. The wells were all drilled & grouted, and all lines run and installed to the geo-unit, in a single day (plus a couple hours the night before and a couple hours the morning after to move equipment). Cost wise, it was almost even with trenching but with a whole lot less land disturbance. I am sure that would not be the case in an area where the earth was not as amenable to drilling.

 

[Country Geek]

Just a quick update, a few days of rainy weather have put trenching on hold until it all dries out.