geothermal pond loop?

[Rob-D]

We heat and cool 2400 sqft plus 1800 heated only. Our unit is 4.5 kW producing about 18.5 kW of heating/cooling.
My observation was that during very cold windy nights (-10 to -15F) the geo run almost constantly keeping the temperature of the liquid at about 80 F. Therefore I have the temperature SP set to 80F for all heating season.
1 ton=3.5 kW=12000BTU/hour. So our geo is 18.5/3.5 = about 5 ton.

Thanks Ladia, sounds like we have similar winter conditions.
Of course several factors have to be accounted for. How well is your place insulated? Room height? Basement? R values?
For instance, I'm essentially heating 1500 sq/ft with R55 in the ceiling (14 foot height in the great room with an insulated basement. (1500 sq/ft)
If I add my workshop in I have another couple of hundred sq/ft. Right now I'm running a .75 nozzle at 140 lbs. which gives me about 106k btu's. I run about 10 to 15 minutes on the hour in cold weather so that means 106/6=17.6k btu/hr. to 106/4=26.5 btu/hr. This is why I'm thinking 2 to 3 tons the most here.
Chilly, the same for your space, it's hard to go by just sq/ft.

Rob

 

[Chilly807]

Exactly... we have 1550 sq feet of living space on top of a hill (read WINDY), plus 450 sq feet of attached garage which is occasionally heated. In really cold weather, (-20C) our system runs almost all the time if we don't have a fire in the wood stove. House was built in 2008, R20 in the walls and R40 in the ceilings, and it's TIGHT. Not quite R2000 spec, but close. No basement, on a slab.

I'd guess at 3-4 ton capacity for yours, but until all the numbers are fed into the software it's hard to say for sure.

Ideally, your system will just barely keep up with the coldest normal conditions you can reasonably expect to see. Too much capacity and you'll have compressor "short cycling" in warmer weather, too little and it'll be overwhelmed by the heating demand.

We've never used our back-up heating coils in the three years we've had our house, but we do augment the geo system with a wood stove, simply because I like wood heat, and the wood is free.

Out strategy has been to set the thermostat at 67 F to maintain a livable temperature while we're at work during the day, then start a fire when we get home at night. When it's time for bed, the usual house temp is ~74 F.

The geo system works well keeping the house at 70 F, but adding a wood fire drives us right out of the house with the added heat. The concrete slab is still quite warm, radiating heat whether the HP is running or not.

Sean

 

[Rob-D]

Exactly... we have 1550 sq feet of living space on top of a hill (read WINDY), plus 450 sq feet of attached garage which is occasionally heated. In really cold weather, (-20C) our system runs almost all the time if we don't have a fire in the wood stove. House was built in 2008, R20 in the walls and R40 in the ceilings, and it's TIGHT. Not quite R2000 spec, but close. No basement, on a slab.

I'd guess at 3-4 ton capacity for yours, but until all the numbers are fed into the software it's hard to say for sure.

Ideally, your system will just barely keep up with the coldest normal conditions you can reasonably expect to see. Too much capacity and you'll have compressor "short cycling" in warmer weather, too little and it'll be overwhelmed by the heating demand.

We've never used our back-up heating coils in the three years we've had our house, but we do augment the geo system with a wood stove, simply because I like wood heat, and the wood is free.

Out strategy has been to set the thermostat at 67 F to maintain a livable temperature while we're at work during the day, then start a fire when we get home at night. When it's time for bed, the usual house temp is ~74 F.

The geo system works well keeping the house at 70 F, but adding a wood fire drives us right out of the house with the added heat. The concrete slab is still quite warm, radiating heat whether the HP is running or not.

Sean

Thanks Sean,
We have radiant in the floors and like the house cool at night (~60ish), days about 62 to 66. I like wood too but certain woods make me sick so I shy away from wood unless it's really cold or going down to 20 or 30 below.
I was thinking about the system this morning and I think I'll run a sensor to the bottom of the pond to see what the springs keep it at this time of year. It's still cold here and this morning it was 12F out so I should get a good idea.
What i may do is run my microhydro and windmills in this summer and see what they give us for energy. I'm wondering if I can feed a preheater to the coils on the compressor from wind and hydro to reduce my total system size.

 

[eepete]

Harold,
Personally I think 4 tons is more than I need, I'll bet this place can run on 3 but he's the pro and I'll give him the benefit of the doubt.
Rob

The two speed compressor is a "must do". You're already in a high dollar area, so the extra cost isn't too bad. Once your at temperature, the lower compressor speed will maintain it. If you're changing the temperature, that extra tonnage will make it happen faster. This is what goes on in our house, and we only see stage 2 in use to maintain the tempurature if it's over 95 or under 10 degrees outside.

Our compressors are a 50% and 100%. Many are now going to 60% to 70% and 100%, which I don't think will be as good but there will still be a lot of benefit. Of course for cooling, the 50% is a double win because the system runs twice as long (but at about half the power so the energy use is the same) so humidity control is excellent. We don't have to run a de-humidifier in the basement.

Tnx for the numbers, Chilly. Our "Achilles heel" is our ceiling insulation. R25. Should have specified R30 to 35, but that put the price of the spray in foam too high. It takes a lot more time to do the thicker ceiling because you have to wait a bit for things to form. Our R25 was a two pass, and more than a few times a whole sheet of foam peeled off. We have a metal roof which really helps especially in the summer down here in hot NC. Cooling cost are more than heating costs. Our walls are R18. Fenestration ratio (widow sq. ft to house sq. foot) is about 11% with one room (the main living room) being the only one with lots of windows in it. Everything else is just a single window.

I've got dampers in so that I can zone the system, but I'm 2 years off from having the control system done. For now, I manually close down the dampers for the upstairs (not occupied) to just a crack, so we still get a lot of benefit from them.

All payback time calculations are maddening. I claim that if everyone could just move their payback periods for these sort of decisions out from 3 years to 7 years, you'd see much more efficient housing and people would have lower bills. It would not surprise me if the lower energy cost were close to the higher mortgage payments due to the more efficient choices. And when the payback time is about the same as your days left, it really gets hard but I like to think of it as leaving something better behind, and hope that the nieces and nephews will enjoy a few extra dollars in their pockets because the place might sell for a higher price. Of course you can only have that attitude if things are going well enought that you're not eating bird food in a 50 degree house :laughing:.

Pete

 

[Chilly807]

Rob,

I take it your current in-floor system was designed to operate with either an electric or oil-fired boiler? The reason I ask that is because of the typically lower water temp generated by a geo-thermal heat source. The hottest our floor water gets is about 90-95 degrees F at the heat pump, which translates to about 85 F slab temperature in the floor itself.

When we were in the design process of ours, the installer commented that they would use 6 inch spacing for the first three runs of pipe in the slab near the edges of the outside walls. The extra "radiance" would help to reduce a "cold edge" in that area. They planned to run 12 inch spacing in the main area of the floor. Normal spacing for oil-fired and electric boilers with a water temp of 120-140 F would be 12 inches.

When it came time to do the actual install, the guys doing the piping (who I think had more actual experience than the designer) simply ran the whole house on 6 inch spacing. I asked about it, they told me I would be able to run slightly cooler water that way, which boosted efficiency considerably. Looking at the efficiency charts for FHP (Florida Heat Pump) afterwards indicated that was indeed the case. The higher you want the hot water temperature to be, the lower your efficiency would be.

Sean

 

[Rob-D]

Rob,

I take it your current in-floor system was designed to operate with either an electric or oil-fired boiler? The reason I ask that is because of the typically lower water temp generated by a geo-thermal heat source. The hottest our floor water gets is about 90-95 degrees F at the heat pump, which translates to about 85 F slab temperature in the floor itself.

When we were in the design process of ours, the installer commented that they would use 6 inch spacing for the first three runs of pipe in the slab near the edges of the outside walls. The extra "radiance" would help to reduce a "cold edge" in that area. They planned to run 12 inch spacing in the main area of the floor. Normal spacing for oil-fired and electric boilers with a water temp of 120-140 F would be 12 inches.

When it came time to do the actual install, the guys doing the piping (who I think had more actual experience than the designer) simply ran the whole house on 6 inch spacing. I asked about it, they told me I would be able to run slightly cooler water that way, which boosted efficiency considerably. Looking at the efficiency charts for FHP (Florida Heat Pump) afterwards indicated that was indeed the case. The higher you want the hot water temperature to be, the lower your efficiency would be.

Sean

Sean,
Yes, I can even run it on a hot water heater.
I put the radiant in about 18 years ago and I was running out of money when I built this place so that limited what I could install. I used Radiantec out of Vermont. The tubes are an inch in diameter and filled with water and Ethyl about 40% if I remember. I have aluminum plates stapled to the bottom of the sub-floor as per Radiantec with a insulation and a reflective barrier below them. Each loop is 200 feet and there are 6 loops running three zones. I have an oil fired boiler running between 105 and 115F off a sensing system I designed. I'm redesigning it this summer using microcontrollers so I can regulate the temperature differential more accurately although the old regulator I built seems to be working relatively well although it's difficult to change the differential.
What I'd like to do is experiment with hydro and wind preheating the water before it hits the compressor in the hopes of saving outside geo tubes but I won't know this until I figure out exactly how much power I'm going to get from my stream. I'll have to build a dam and do a flow test. I was just thinking this morning that I may go with a Banki wheel because I have relatively low head.
I've been monitoring the wind in my front field for a couple of years and it will give me very good wind which I'll feed to my inverters to run the house along with my solar panels and then to a dump load (the compressor preheater).
It should be an interesting summer as I just got a 20k grant to run a 6.8kw intertie, right now my panels aren't running back to the grid.

Rob

 

[rustythe4x4]

When we built out house, we installed a 6 ton NextEnergy unit (forced air, no radiant) and had 12 vertical loop wells bored. the wells are 110 feet deep, the manifold is 10 feet below the surface. This is a closed loop system. We live in a cold climate (its 15 below celcius on March 26) and have NEVER turned on the back up heat, nor has the unit even called for the back up unit to be turned on for 3500 square feet. Our payback is calculated at 3.5 years when compared to a natural gas installation.

I researched vertical versus horizontal before deciding on a unit (all closed loops, open loops are NOT recommended in our climate/water conditions) and found that horizontal loops were not as efficient unless 10 to 15 feet below the surface, due to creeping frost levels, which can reach 7 or 8 feet. The next efficient was a horizontal loop with a "dip" in an existing body of water, but the warning was it can freeze the pond completely, even if it is 20 feet deep - my loop temperatures run at MINUS 10 celcius. The most efficient was vertical bored wells (mine is 4" bore with 1-1/2" poly pipe), normally 2 wells per ton for efficiency. Getting the vertical bored wells into ground water is even better, and mine are into about 70 feet of ground water. Calculated efficiency is 350% - whatever that really means.

Bottom line is find a GOOD REPUTABLE and CERTIFIED installer, and ask a lot of questions.

 

[Chilly807]

Bottom line is find a GOOD REPUTABLE and CERTIFIED installer, and ask a lot of questions.

Amen !

 

[Chilly807]

Sean,
Yes, I can even run it on a hot water heater.
I put the radiant in about 18 years ago and I was running out of money when I built this place so that limited what I could install. I used Radiantec out of Vermont. The tubes are an inch in diameter and filled with water and Ethyl about 40% if I remember. I have aluminum plates stapled to the bottom of the sub-floor as per Radiantec with a insulation and a reflective barrier below them. Each loop is 200 feet and there are 6 loops running three zones. I have an oil fired boiler running between 105 and 115F off a sensing system I designed. I'm redesigning it this summer using microcontrollers so I can regulate the temperature differential more accurately although the old regulator I built seems to be working relatively well although it's difficult to change the differential.
What I'd like to do is experiment with hydro and wind preheating the water before it hits the compressor in the hopes of saving outside geo tubes but I won't know this until I figure out exactly how much power I'm going to get from my stream. I'll have to build a dam and do a flow test. I was just thinking this morning that I may go with a Banki wheel because I have relatively low head.
I've been monitoring the wind in my front field for a couple of years and it will give me very good wind which I'll feed to my inverters to run the house along with my solar panels and then to a dump load (the compressor preheater).
It should be an interesting summer as I just got a 20k grant to run a 6.8kw intertie, right now my panels aren't running back to the grid.

Rob

It sounds like you've got quite the operation there... I wish I had the time and initiative to do something similar.

Sean

 

[Redneck in training]

Our compressors are a 50% and 100%. Many are now going to 60% to 70% and 100%, which I don't think will be as good but there will still be a lot of benefit. Of course for cooling, the 50% is a double win because the system runs twice as long (but at about half the power so the energy use is the same) so humidity control is excellent. We don't have to run a de-humidifier in the basement.Pete

Hydronic system differs from forced air in a sense that it has a heat/chilled liquid buffer tank that provides load for the heat pump independent of house heating/cooling demand. The cycling is a function of heat pump power relative to size of the tank. It seems to me that all hydronic heat pumps are single speed.

Another thing I would mention is to select heat pump optimized for your climate. They are not created equal. There is a difference in heating swimming pool in Florida and heating house in Canada.

When we decided to use geothermal system we didn't look at initial cost at all but considered factors such as comfort, quiet operation etc. At the end (six years later) it already paid for itself in energy saving.