New geothermal install

[woodgeek]

Interesting current thread on DX systems here:

http://www.greenbuildingtalk.com/Forums/tabid/53/aff/13/aft/79832/afv/topic/Default.aspx

I think that thread summed it up well refrigerant (DX) versus water/glycol loop. I think the soil side
thermal conductivity has to be limiting in most cases (except in aquifers that are slowly 'flowng'). So
the higher eff claims need to be based on side by side field reports. I could believe that there is
less pump work if the refrigerant is lower viscosity.

Personally, the heart of all these systems is the compressor, and the key to longevity is keeping
foreign matter out of the compressor wear surfaces and keeping the oil in the motor. It seems that
many of the problems (at least with ASHP) are from sloppy installers letting contaminants into the
refrigerant loop lineset. So, I would be much happier with my refirgerant loop being contained in
a factory sealed unit, rather than running through 100s of feet if field installed tubing.

 

[Ehouse]

google Heatgreen home heating for another interesting read.

I wonder if a Trombe wall or solar water heater loop hooked into a system and used on sunny days would give a ground loop time to recharge?

Ehouse

 

[DickRussell]

....I think the soil side
thermal conductivity has to be limiting in most cases (except in aquifers that are slowly 'flowng').

That's basically it for many systems, whether DX or buried plastic slinky loops. There are two factors on the plus side for a DX system. As seen in that equation I posted yesterday [#21], the total resistance to heat transfer (1/U) at any stage of the overall system is the sum of the fluid, ground, and tube wall resistances. The fluid (refrigerant) and tube wall resistances in a DX system are lower than for water/glycol flowing through a plastic tube. But even if they were so small as to be insignificant, there still is the resistance to heat transfer on the ground side, which selection of fluid and tube material won't change. So yes, the soil side usually is limiting.

The second aspect of a DX system that is a plus is the elimination of one heat transfer step. In a design with water/glycol fluid flowing through a closed loop, there is heat transfer from the ground to the fluid (we're talking heating mode now), a second heat transfer step that moves heat from the fluid to the vaporizing refrigerant within the heat pump unit, and a third step where hot condensing refrigerant from the discharge side of the compressor gives up heat to air moved by the blower (or to water in a hydronic system). The DX design eliminates that first step; ground heat vaporizes refrigerant directly in the buried copper tube. Each heat transfer step requires a temperature difference for any heat to flow, even if it's only a few degrees. Having a second temperature difference between ground and ultimately the vaporizing refrigerant means that the refrigerant must be vaporizing at a temperature (and pressure) that much lower than for a single heat transfer step. That means more work for the compressor to get the vaporized refrigerant up to a pressure (and thus temperature) where it can condense against warm air in the final step. More work for the same amount of heat delivered means lower coefficient of performance (COP), the usual measure of efficiency for heat pump systems in heating mode.

Finally there is that already discussed matter of getting replacement heat into the soil next to the buried tube and taxing the heat capacity of the ground in the excavated/backfilled area. As more heat is drawn from a chunk of soil, its temperature drops and one of two things must result. Either the refrigerant vaporization pressure/temperature must drop to compensate and keep the heat flowing, which reduces COP, or the reduced temperature difference simply limits the overall heat transfer rate and thus system capacity. It's not enough to reduce fluid and tube wall heat transfer resistances and to eliminate a heat transfer step by using a DX design and not consider the soil side limitations.

In the case of a ground loop run into an aquifer area in use for domestic water supply, running the woodstove for heat to give the ground around the buried coil time to regain heat won't hurt, but it probably isn't needed. The wetness of the ground and any movement of water through the area can move an awful lot of heat past the coil.

 

[woodsmaster]

Do the fans run all the time on these systems ? I recently worked on a house with geothermal and I don't think I ever heard
the fan shut off.

 

[Jerry_NJ]

My system has a two speed fan, the lowest speed is very quiet, but it can be heard. Even the high speed isn't noisy. The fan also has a third lower/slower speed that can be set for continuous run at the thermostat. I turn that off when I am not heating or cooling... even if I have the system on but don't expect to see much run time. The installation recommendation was to leave the fan on all the time and leave the HP on all the time in the automatic mode, it cools or heats based on settings and "never" needs to be touched again. I have a hands-on guy, and we like the windows open when the weather permits, so in the spring and fall the HP is completely off, including the low speed circulation fan. This fan is a plus when I'm doing serious wood heating, it help s move that heat around the whole house.

 

[sesmith]

Do the fans run all the time on these systems ? I recently worked on a house with geothermal and I don't think I ever heard
the fan shut off.

They do work differently than a conventional heating system in that they're sized much more closely to the heating needs of the building, instead of being over-sized, as are most conventional systems. They also put out cooler air. So as the temperature outside drops closer to their lower design temperature, the system runs more and more of the time in a given hour, until it's on all the time. Long run times like this are actually a more efficient way for them to run, and doesn't mean that they are having trouble keeping up (so long as the system is sized correctly). What this does do, is keep the house temperature very even. Mine rarely is any different than the set point I have it set to. It also has a variable blower on it and a 2 stage compressor to further control things.

My system will start running continuously at temps around 15 degrees or less, give or take. When it goes into the single digits, second stage will kick in as well. Usually in the early morning after a night a little below zero, the aux strip heater will come on for a few minutes periodically, to help the system out ( which will also be running in second stage). This is a system with a winter design temp of 2 degrees and a balance point where aux heat may be needed of 7 degrees.

 

[woodsmaster]

Thanks for the info I wondered about that. Seems like a lot of elec. to run the fan all the time. The house I was working on was medium in size and he said he had around a $300.00 elec. / month for 2 adults and a baby. I circulate water, have an old house andfamily of 5. My elec bill is less than $150.00 / month in the winter, but I also burn a cord a wood a month in the winter and a little in the summer for hot water. In the summer my bill goes up to 200.00 or a little more becouse of the air cond.

 

[woodsmaster]

Don't get me wrong I Like geo thermal and it's much more convienient than burning wood. I just don't like air blowing around.

 

[Jerry_NJ]

On my geothermal I can set it so the fan runs only when heating or cooling, the "run all the time" is my choice. And, when using my wood stove (fireplace insert) the HP fan running all the time help distribute the heat that is building up in the room with the stove - a big plus. With the duct work I have the noise of the fan in low speed is almost imperceptible.

I agree with the practice of not "wasting" energy, and that is why I set the fan to run only on heat/cool when I don't want to circulate air around the house. In fact there are several months a year, suppose at least 4, that the HP is completely off. P.S., goe or air-to-air, a "super heater" exchanger with the water heater turns air conditioning (cooling) wasted heat into hot water, great, this is truly "free" hot water... assuming one is air conditioning anyway.

 

[sesmith]

Don't get me wrong I Like geo thermal and it's much more convienient than burning wood. I just don't like air blowing around.

I see you move your heat around in liquid form. That works too. The air blowing with our new system is almost unnoticable. Very quiet, but we also replaced and reconfigured all the ductwork when the system was put in. Its quieter than all the fans I had running when we heated with wood. Our old forced air oil furnace was a dust maker. When the sun was right, you could see all the dust being blown around when it came on. The new system has a large merv 11 filter in it, so it works as a whole house air filter as well. FWIW, I couldn't buy firewood at $200 / cord (going rate here) and heat the house for less than this system costs to run. ( I never did buy the wood, though, when I did heat with it, as ours came from our wood lot...saved a lot of money that way).

 

[johnny1720]

I have been watching the forecast like a hawk lately. There is no cold snap in the near future. We have had daytime temps in the mid 30's to mid 40's. We are only getting down into the 20's at night. I have been reading my meter almost every day and we are using about 58kw per day which is an increase of about 18kw per day. So that means I am paying about $2.00 per day to heat the house when it an average temp of 34. I cant burn my pellet stove for less than $8.00 per day. I need to burn at least two bags of pellets @ $4.00 per bag.

So far so good with this investment.

 

[Jerry_NJ]

Looks good, congratulations. But, what?, 58KWH per day, or 40 KWH when you were not heating with electricity. That's a lot of "background" power consumption. $2 for 19KWH, that's 11 cents per KWH, wish were were that low, Jersey Central Power is charging a bit over 16 cents per KWH. It seems you too are all electric.

Or temperatures here in North Central NJ are a bit warmer than yours, but only a few degrees. Looking back to colder weather, more like you are having now, I'd say we were using about 45 KWH per day, including heat. Now we are all electric, including hot water, cooking washer/dryer, refrigerator, well... lights, the only other "utility" bill we have is telephone (and TV/Internet). And, yes, I burn a cord+ of season hardwood a year which cuts back on the KWHs on those months that I burn wood. Some of this wood is scavenged, included from my property, so I can take the work as exercise and conclude that wood is free less the cost of gas and wear and tear on my equipment.

In any case you are having the same experience I am having, I use wood for reasons already stated, not to save money over the cost of geothermal heat.

 

[johnny1720]

Yea 40kw is what I usually use per day. My electric rate was the 17 cents an hour then I got talked into to using an alternate energy supplier. Then it dropped to the 11 cents. I have a well that is 60 feet deep/electric range/electric dryer and now my heat is 100% electric. I am going to have my well looked at and see if that is drawing when not being used. I have always thought it might be but I never had a way of checking.

 

[Ehouse]

I had that problem with my well, turned out to be a crack in the pipe just above the check valve on the pump allowing the water to drain back and lose pressure. Look at your pressure guage and see if it holds steady after the pump stops.

Ehouse

 

[Jerry_NJ]

Right, with a deep well there is always (as far as I know) a holding tank that has a trapped air chamber which compresses when the pump is supplying more water than is being used (normal, in my case I can have the garden hose on full blast and the pump still cycles at about a 50% duty cycle). When the upper pressure limit is hit, the pump should shut off. As noted, there should be a pressure gauge and you should be able to see it pump up, stop, and leak down (assuming you have something on, say the kitchen faucet). Of course, with no use of water, the pressure gauge should just set at a reading, not moving up or down.

My well is about 100 feet and the pump is 220 Volt (telling outright it uses a lot of power). I think it is about 1 HP, or in the neighborhood of 750 watts. That is 0.75 KWH per run hour. If I assume only 500 watts, that running full constantly would run the meter up 12 KWH per day. In any case check it out, but I consider it unlikely that your pump is running all the time. You didn't mention how many people live in your house, how good people are at turning off lights, and if you're using tungsten bulbs, not CFL or other high efficiency lights. Lots of baths, laundry, dish washing and lights will put a lot of KWHs on the meter a day.

As for electric rates, I too buy from a third-party supply, cuts a few 10ths of a cent per KWH off my bill, and that cost is in the neighborhood of 11 cents per KWH, bur I also pay about 5 cents a KWH for delivery, thus the cost is 16 cents per KWH. That's the way it works everywhere the electric power market has been opened to competition. There is still no competition for the delivery system, all the money invested in wires/transformers/repair-crews... so even if one buys power from the (traditional) supplier, they will still see a charge for generation and one for delivery. Compare their generation cost with the cost of a third party supplier, don't compare the 3rd party supplier cost to your old total cost per KWH.

Edit: corrected 7.5 KWH to 0.75 KWH in second paragraph.

 

[sesmith]

Yea 40kw is what I usually use per day. My electric rate was the 17 cents an hour then I got talked into to using an alternate energy supplier. Then it dropped to the 11 cents. I have a well that is 60 feet deep/electric range/electric dryer and now my heat is 100% electric. I am going to have my well looked at and see if that is drawing when not being used. I have always thought it might be but I never had a way of checking.

Find someone with a multimeter with a clamp on amp probe on it, who is familiar enough with electrical work, to check for a draw on the pump circuit. This will have to be done from inside the main panel. There should be no current draw when the pump's not running. It wouldn't be a bad idea to check any of your circuits that have wiring run underground.

Another thing you might try is to buy a "kill-a-watt" meter, to use around your house to check all your plug in appliances. It can be a real eye opener. I found out just how much electricity was used by our stock tank heater a couple of years ago. I've since built a superinsulated horse watering tank that cut that usage almost to zero. I also found that our old dehumidifier in the cellar was using a lot of electricity and basically wasn't doing much of anything for the humidity...since replaced with a much more efficient one. Those 2 changes cut our electrical use by a third.

 

[johnny1720]

Yea 40kw is what I usually use per day. My electric rate was the 17 cents an hour then I got talked into to using an alternate energy supplier. Then it dropped to the 11 cents. I have a well that is 60 feet deep/electric range/electric dryer and now my heat is 100% electric. I am going to have my well looked at and see if that is drawing when not being used. I have always thought it might be but I never had a way of checking.

Find someone with a multimeter with a clamp on amp probe on it, who is familiar enough with electrical work, to check for a draw on the pump circuit. This will have to be done from inside the main panel. There should be no current draw when the pump's not running. It wouldn't be a bad idea to check any of your circuits that have wiring run underground.

Another thing you might try is to buy a "kill-a-watt" meter, to use around your house to check all your plug in appliances. It can be a real eye opener. I found out just how much electricity was used by our stock tank heater a couple of years ago. I've since built a superinsulated horse watering tank that cut that usage almost to zero. I also found that our old dehumidifier in the cellar was using a lot of electricity and basically wasn't doing much of anything for the humidity...since replaced with a much more efficient one. Those 2 changes cut our electrical use by a third.

I have had a kill-a-watt meter for over 5 years. I have a huge spreadsheet with appliances listed and how many KW they use. Previous to me replacing my electric hotwater heater with a propane tankless I was spending almost almost $250 per month on electric. I do have an amp meter at work with a clamp on it I should bring it home and try it.

I think the culprits are

-my dryer seems to only dry on high
-my well is below grade (water shoots out of the top of it)
-I have an old double door fridge that is not in the best shape, i have not ran the KW meter on it yet.

 

[woodsmaster]

Is it possible to have geothermal radiant slab heat ?

 

[pdf27]

Is it possible to have geothermal radiant slab heat ?

That's the recommended method of installing them, at least in Europe. Standard advice over here is that they're only marginally worth installing if you don't use radiant floor slabs!

 

[Ehouse]

Radiant slab heat? Most definitly. The key factors seem to be high mass, super insulated shell, well insulated slab (edges and under) and high flow rate through the tubing. As an example, my home (under construction) has a design floor temp. of 81* to maintain 68* in the living space for 3/4 of the expected highest demand conditions. A second unit (water to air) will provide extra heat as needed as well as cooling and DHW.

Ehouse

 

[woodsmaster]

Is it possible to have geothermal radiant slab heat ?

That's the recommended method of installing them, at least in Europe. Standard advice over here is that they're only marginally worth installing if you don't use radiant floor slabs!

Then it seems to me that would be the best way to go if building new. A lot less electric to circulate water around then to blow air.
Most folks over here do the air method probably for the ease of adding central air.

 

[Jerry_NJ]

Slab heating ain't for crap at cooling (air conditioning), that's what a heat pump is all about, moving BTUs both ways. Forced air provides a central means to filter the air and a means to transfer heat and cool to all rooms, upstairs and down. If one can afford both, then a radian slab could be a nice addition, but more economical to heat? I doubt it.

Johnny you haven't said what your needs are. How many square feet are you conditioning, how many people, how much cloths drying... 50 KWH per day in the cold days may not indicate any real losses. Your usage doesn't seem overly high unless you are living alone in a well insulated house of less than 1,500 sq feet.

You can see what the house is using when it is supposed to be off by watching the meter. If you have an older analog electric meter it has a rotating disk, for most, mine, one rotation is 7.2 watt hours. A digital meter must also have some sensitive readout. Turn off you heat, make sure the hot water heater is off, better too, unplug the refrigerators/freezers, turn of the TVs.... most lights and go out and look at your meter. If the disk I mention is rotating more than once in a couple of minutes (one per minute results in 60 x 7.2 = 432 WH) something is running that you should know about. If you really shut down the house, the disk should just "creep" around... if you can get the house completely off, the disk should stop.

Again, 50 KWH per day for all energy uses isn't a lot. Even at resistive heat 50 KWH is 170 KBTUs, someone using heating oil may be 110 KBU per burned gallon, or 1.5 gallons, at $350 that's $5.25. At my electric rate of 16 cents per KWH $5.25 buys me 32 KWH. Of course, most homes use more than 1.5 gallons per day in cold weather. Just trying to develop a parallel to what 50 KWH represents. With a heat pump you're getting way more than 170 KBTUs out of your 50 KWH. I use about 45+ KWH a day in this moderate cold weather, and with 2,000 square feet two story well insulated I'll place the this provides at least 275 KBTU heating per day/night, or little more than half of my power consumption.

 

[woodsmaster]

It certinly would be more economical to heat by circulating water. I'd be willing to bet it would Knock at least $50.00 a month
off most installs electric consumption if not more. It's the cooling that the slab isn't as good at.

 

[johnny1720]

Johnny you haven't said what your needs are. How many square feet are you conditioning, how many people, how much cloths drying... 50 KWH per day in the cold days may not indicate any real losses. Your usage doesn't seem overly high unless you are living alone in a well insulated house of less than 1,500 sq feet.

-I am heating a 2400 square foot plank house that was built in 1860, when I say plank I say until I moved in and started remodeling there were not studs on the walls. So if you can picture 18" to 36" wide planks going vertical between the floors on all outside walls and interior walls. There are two layers of planks everywhere. On the inside was plaster and lathe and the outside is tar paper and clap boards. So the thickness of the walls was only about 4 inches. I have since studded out more than 1/2 the walls and insulated and drywalled. I have replaced all 38 single pane original windows with new vinyl replacement windows. I also have about 45 inches of blown in insulation in the attic of my house. I either burn 2.5 bags of pellets for $10.00 per day or I burn about 4 gallons of fuel oil for $16.00 per day.

-There are 2 adults, 2 children ages 3 and 9 weeks.

-Last winter was pretty long and rough, i burned 2.5 tons of pellets and 800 gallons of fuel oil. The winter before that I used 650 gallons fuel oil and 2 tons of pellets. And to tell you the truth this is a significant improvement from what I used to pay. The first full winter I was in this home it cost me nearly $5000 to heat this place.

-My hot water is heated via tankless on demand, I installed this 4 years ago (it has already paid for itself)

-Prior to Geothermal I was using about 40kw per day on average according to my electric bill, it has increased to about 58kw per day.

-I have CFL bulbs almost everywhere, and all appliances are energy star including, dishwasher/freezer/beer fridge/old double door fridge which is also suspect.

 

[Jerry_NJ]

Sounds like an interesting house, I am not familiar with the construction.

Sounds like you've about got your arms around the heating cost and 58KWH a day for all what you said seems reasonable to me... indeed very good, and a way better than $5K in heating oil. Seems heating oil (is that what you make hot water with) is $4 a gallon, the way gasoline is going I suppose heating oil is on its way up too, thank God spring is almost here.

Does your HP have a hot water tap on the "super heater"? You'd need a tank, but as you can see the energy gains running a heat pump are significant. Better yet, in the summer when you are throwing heat away (into you ground loop) any heat going into you hot water needs is free...just the cost of the tank. I don't know how that would work with your investment in the "on demand" hot water, but if the tank was the feed to the on demand, the on demand would have to provide much less temperature rise, in fact none when the tank is full of 150 degree water, or whatever you HP is capable of generating.

Keep up the good work and enjoy your investments in energy conservation while looking out the window at cold/hot weather.