Pond Boss Forums INTRO Questions & Observations Geothermal Heat Pump

This is one reason I wanted to let you know that it is not complicated, unless you want it to be. Radiant floor heat is it's own system, whether it is heated by geo or otherwise. Using geo for forced air heat / AC is not any more difficult than a conventional system. Let the geo system heat the tank of water and let the radiant system do it's own thing. Personally, I let the geo system heat my domestic hot water, and keep the radiant floor system seperate.

I have been told 500' of pond loop is required per ton, and that is what I have. It might be different in other areas.

I bet a geo manufacturer could answer your questions and recommend a good dealer in your area.

I would hate to see the description of Ladia's gee-whiz system discourage anyone.

Geothermal is supposedly very popular now. Especially for new construction. The guy who sold the system to me told me (he installs the ground loops) that he was booked up for several years in advance. Now they have new drill that can pull the tubes underground without major digging. I also think that the installers got much more skilled, since I installed my system, (well there is a software) in calculating all the required specs. If you don't need AC (you can always add it later) the floor heating with geo is not much more expensive than forced air especially if you can lay the tubes by yourself.
By the way most of the utilities also sell the geo system.
Obviously the best and cheapest heating is insulation. Combined with HP it might also be the least costly to operate. If you use geo for heating only it is about as complicated as forced air.
The two system could coexist several ways. I would use two separate heat accumulators each with its own temperature control and circulation pump. One could be set to floor heating temp 90 - 110 F and the other to forced air temperature 160 F with house heating demand priority. Then you would have to replace the furnace with an air handler or add the air handler in series with the furnace so you will have a back up heating.

I agree. I think the controllers that would do the job without exotic solutions are on the market. Since the geo is more or less mainstream now the installers are better trained and more adept to do it right.
Geo is hard to beat in cost of operation even if the utility starts charging the retail rate (most utilities charge the wholesale rate now).

Ladia,
You mean you have one meter for HVAC and another for the rest of the house?

When you said above "using geo for heating only" you lost me. My system is a forced-air heating and cooling system, just like most conventional heat pumps. This is it's only function, the domestic hot water is just icing on the cake.

I know they make geo units that only do one thing...heat water. Some people use them to heat swimming pools and radiant floor systems. Is this what you were referring to?

Is your radiant floor in concrete or under a wood floor?

Yes we have two meters. The utility charges the wholesale rate just in the heating season.

There are three basic Heat pump arrangements: Heating only, cooling only and reversible heating/cooling. To achieve maximum efficiency it is important to use the heat pump optimized for your particular climate and type of the heating system such as floor, hydronic (with radiators) or forced air.

We have floor heating with PEX embedded in concrete slab. Since the efficiency of the heat pump is inversely dependent on the temperature differential the floor heating is probably the most efficient because it has the smallest temperature differential.

Needless to stress the obvious: The best heating is insulation, insulation and insulation.

Anyone here take advantage of the $2000 tax credit for geo installed after Dec 07 ?

Ladia,
That explains why your system is more complicated than mine. Again, mine is strictly forced air heat & cool, with the super deheater heating the hot water. I have pex tubing in the entire basement floor, in 6" of suspended concrete in the kitchen, and 3" suspended concrete in the master bath, but none of it is hooked up yet. I have not figured an easy way to use the geo system to warm these floors, since I am pretty much using all of the hot water the system produces for domestic. In fact, my electric bill stayed the same last fall when we quit using the A/C. The electric water heater had to take over. I might as well keep running the A/C.

I am thinking of just using a small water heater and pump to circulate 90 - 100 degree water through these floors. It won't be so much to heat the house, just enough to take the chill off the tile floors.

As you mentioned earlier, with radiant heat, especially in concrete, you can't just decide to raise the temperature because you are chilly. It takes several hours to make an adjustment, both up and down. Does your system look at the temperature and trend outside to decide that it's time to start (or stop) warming the floors? I don't know if I will need this or not, but it is something I would like to learn more about.

Seems to me that I got myself deep in the discussion about geothermal heating cooling so I should make one thing clear. I am not an expert on geothermal heating but I learned a lot while implementing geo in my own house. My intention is to share my own experience with my own geo system to help other people to avoid mistakes I made and/or help them to be better informed about the issues associated with the geothermal systems. My background is in control systems. I install and set up control systems for industrial processes (such as oil refineries and chemical plants) for living. Therefore I decided to design and make my own control box because of the shelf product was not available at that time. It was also fun project but if you ask me if I would do it again the answer is NO. I would do it again only if there isn’t an alternative.

My system is complex (not necessarily complicated) due to the fact that I have several zones each with individual temperature control. I have integrated whole house filter with the AC. The filter uses the same ducts but otherwise it is separate unit with its own fan and heat recovery etc.
Both the heat accumulator as well as HW heater have individual temperature control. I might add AC with all associated temperature and occupancy control for the garage/shop later on.
Switching from heating to AC is automatic. We have one "smart" thermostat (located in the kitchen) that has built in an algorithm to select heating and cooling mode but I found that it could get “fooled” in example by baking Christmas cookies that generates a lot of heat or when we used a fireplace etc. Therefore I added a logic that checks if the demand for heating or cooling is sustained and then switch. The heat accumulator is "charged" (kept hot or cold) only if there is a demand for heating or cooling. The original control system kept the accumulator charged even when there wasn't demand for heating or cooling for several weeks at spring or fall. All pumps are cycled every day for one minute to prevent sticking due to long inactivity etc. The control box also controls the cycle for HW recirculator so there virtually instant hot water from the faucets but the recirculator doesn’t need to run continuously.
The temperature in the heat accumulator is fixed so the system doesn't look at ambient temperature but I might add the sensor just for information.

I wouldn’t use direct heat for floor unless you can’t justify the cost of adding the floor heating to the HP. The HP will heat the floor four times cheaper at retail electricity cost and about 8 times cheaper at wholesale cost. The cost and complication will depend on your system. I don’t know if your system has separate fan coil or if it is all in single unit similar to furnace. It might or might not have heat accumulator and/or even provision for floor heating hookup (in ex: built in heat exchanger and circulation pump). One thing you need to know about floor heating is that the floor is cold to touch. It feels warm only if you have socks or shoes.

Ladia,
Mine is a self-contained unit (Waterfurnace)
It has a circulator pump built-in for the super-deheater, which can be switched off it you don't use it. (Why would anyone not use it?) It could be used for radiant floor heat, but I really think I use most all of the hot water it can make. At least in the winter. In the summer, I have both the passive and active 80 gallon tanks full of free hot water. But no need to heat the floors in summer.

Interesting conversation and observations.

MarkECIN, I don't know if you're still having trouble with your electric heating strips coming on too often, but if you are you might check that your water lines to the geothermal unit aren't freezing. Our unit is in an uninsulated attic area and we had some really cold days right after getting it installed. When the lines froze, the geothermal heat stopped working, when they thawed, it started working again. This can make it difficult to diagnose! If this is the cause the solution is wrapping the pipes or possibly building an insulated closet around your unit.

We're using a Climatemaster and we had our HVAC guy set us up so that the heat strips never come on automatically. Our thermostats (honeywell touch screens) still shift between indicating "heat" and "aux heat" as if they're using the auxiliary heat strips when needed, but it's really always using only the geothermal. If we ever decide we need the electric heat for some reason we can manually switch to "emergency heat" on our thermostat. I think this is a much better set up since if the geothermal isn't working or keeping up for some reason I'd rather find out by getting too cold than by a huge electric bill a month later. Of course, this might not be a good idea if you're leaving a house unattended during cold weather, but for us it works great.

Jersey,
Any conventional AC or Heat Pump unit can have a desuperheter installed for heating water. It's not restricted to geothermal. However, with geothermal units it's typically much more convienient as many have the desup built in or as an easily installed option.
In cooling mode the desuperheater acts as additional condensing capacity utillising some of the heat wich would be rejected (to the air or pond loop for example) to heat water. There is no reduction in system capacity.
With a heat pump in heating mode the opposite is true. There is a reduction in system capacity (10-15%) if the desuperheater is used.
So this is definatly one area where seasonal adjustments or an extended control set might make sense. For example, one wouldn't want to be paying to run the heat stips on high demand nights because 10% of their system capacity is diverted to heating water while they sleep.

Hot water demand tends to be transient and there is typically very little relation to demand and outside temperature. It's certainly important that the controls for HW heat be setup properly. Ladia and I had a discussion offline about this. Thier system was initially installed with no temperature control for the desuperheater. The desuperheater ran all the time the system was on regardless of the HW temperature. Other than being inefficient, there is a danger of scalding in a situation like that.

This is certainly one area I would quiz the installers about if I had one of these systems. It's important to know the temperature settings on the hot water heater and desuperheater settings and make sure they are set properly. It's information that you need to know anyway so when the HW heater is replaced it can be setup properly. The desup settings should be less than or equal to the HW settings. Some systems have additional controls for the desup circuit and can turn it off based on staging for example. I'd ask if this is being utilised and how its setup. It may be an option you have paid for and the installer never bothered to turn it on.

I agree with most statements of tejasrojas with one exception. If the building has large thermal mass such as floor heating embedded in concrete floor I would set the desuperheater temperature higher than the hot water heater thermostats to give it a preference. Loss of the heating capacity caused by heating hot water is usually only temporary (It will not cause noticeable discomfort) while it is significantly cheaper way to heat the hot water.

The logic that turns the heat strip on in forced air system should have reasonable time delay so the direct heat will turn on only when it is certain that the heat pump can't supply sufficient heat. It shouldn't turn on instantly when the temperature drops too low below the set point. In example when door is or window is opened for short time. I personally would disable the heat strips and re-enable them only in emergency. The short loss of comfort is not worth the money it costs.

I just learned the hard way why not use custom-built control systems.
I am currently on a business assignment overseas and will not make it home for at least one more month. My wife reported there isn't hot water in the house. The logic in my PLC disables hot water heater anytime the geo is running and re-enables it when it stops. That way the geo keeps the water heater charged preferably by the heat pump. The problem started when PLC requested start of the heat pump but it didn't start for at this point unknown reason and thus kept the water heater disabled. Then I spent few hours of figuring out how to override the PLC and instructing my wife how to reprogram the HP to stand alone mode, latch primary pump relay to always on, set heat accumulator SP in PLC cabinet to low temp so the logic would think that it is hot and didn’t try to start the heat pump thus disabling the hot water heater etc.
So now the house is warm and hot water is available.
Lesson learned:
The emergency PLC bypass should be built in the system, tested and detailed override procedures written. In other words I have to redesign the whole thing. It will be fun project. Well, until something unexpected happens again.

Actually did get the problem resolved. Electric transformer wasn't big enough to keep everything going, electric company replaced.

I'm reading everything y'all are writing as I have to learn now that we have this geothermal pond loop. But I cannot say it enough-- I don't miss those high LP bills we used to get!

Ladia, I just have to say this--you are a "wealth of information" and if gained by experience, I hope to someday be as smart as you about this geo stuff to where I can trouble shoot some problems myself too. Thanks for your input. I'm catching up on my reading on the forum. d

I have reading this forum with interest and it is VERY informative! I like to read about people who have 'been there, done that' before deciding on something. We live in south Alabama where the main concern is hot, humid summers. We are building about a 3 acre pond and a 'retirement' cabin (more like a house...2500 sq ft)using mostly all reclaimed wood and beams from old houses(will be timber frame.) We are very interested in geo thremal for the pond. It almost doesn't make sense not to go geo!I have read through these post and have a few questions. When you mention the power bill being MORE, is that just for running the system? I guess since we don't use propane gas at all,(we have an all electric heat pump) our power bill should be LESS, right? Right now our power bill runs around 250.00-300.00 a month, whole house. About what kind of savings should we expect from the geo? Also, looked at the Slim Jims. Has anyone used these and how does the price compare to the coils? ONE more question....does anyone that lives in the south feel like the air inside in the summer is comforable, in other words, not humid? I think I read somewhere this system is also a dehumidifier. We are also looking into siting the cabin to take advantage of passive heating/cooling. The south side will have quit alot of glass and am worried about overheating. Thanks for all your help! This is an awesome forum!

Southernbelle, welcome to Pond Boss. We're glad you found us.

Thanks JHAP! You'll probably see me around here alot. Going to need some advice on the pond too! Hoping to start in a few weeks. It's stream feed, so don't think it will be in danger of going dry with the geothermal. Also going to install a dry hydrant. Any forums here on that?? The cabin will be a good way from the road and the hydrant will also be a plus for insurance. Sounds like this is going to be a working pond!It will heat/cool, supply hot water, put out a fire, provide fish and hours of enjoyment. Anything I'm missing?

SB, I'd advise you to start a separate thread. I believe that several folks here have dry hydrants but I'm not positive.

You came to the right place for advice, some of might even be correct advice.

I found the dry hydrant thread-sorry!! Didn't think to do a search-duh!

Southernbelle, on our geo system we have the fan that runs constant for filtering the air (they just recommended to run it that way and we have been, you don't have to)so it costs a little more to run it that way. We do have a dehumdifier that we had on our previous system that we had the installer hook up to our geo system. Works fine that way. (PS...I'm originally from Louisiana so I know all about those hot humid summers).

Ladia, what's your take on running the fans constant? I'm still learning here. d

Southernbelle,
Check out
http://www.tractorbynet.com/forums/
IIRC there were several dry hydrant threads there.

Matt

thanks Matt--who would have thought to look there. You guys know all the secrets!

Hi Sbelle...welcome.
Your project sounds like a wonderful undertaking. Please, be so kind as to allow us to tag along as it progresses. Start a thread for your pond...and...please start a thread for your home construction. Get a photo hosting acct established and bring us pics and descriptions. We love it. The inspiration that you provide is the fee we charge to play.
-
Is this the dry hydrant thread that you found?

Fair enough, but this scenerio is correct only if the aux heat is disabled. Otherwise, when outdoor temps fall to 85-100% design temps, aux heat is going to kick in to maintain the hydronic loop. It's really more of a question of capacity and how often the system demand is near or at full capacity.

I mention this because, as you know, some of the desuperheater controls are quite primitive. The default mode for one paticular unit consists of nothing more than a high limit set at 140F attached to the desup inlet line. The desup runs anytime the return water is under 140F even if aux heat is on. Adjustment consists of moveing the high limit to the desup output to lower the temerature. One has to pull the fuse to disable it.

Other systems have adjustable desup controls that one can match to the WH control and have additional control logic to shut down desup when aux heat is called for.

Some systems extend this control set with multiple stages so desup can be shut down before aux heat to allow the system time to meet the demand while running at full heat pump capacity. If the system still cannot meet demand additional stages of aux heat are turned on.

The better control for hydronic systems monitor outdoor temperature and use this information as part of the control loop. I think this is clearly the best way as the floor loop temp can then be matched to demand. The desup can be shut down as system reaches max capacity.


I have never disabled ours as I have to travel too much to see it as worth the risk. Because ours is an air source heat pump, we make an attempt to provide suplementle heat (wood stove fireplace insert) whenever the outside temps fall below ~35F for an extendend period. This is not because of aux heat, but we try to minimise system usage when defrost cycles are required.