Pond Boss Forums INTRO Questions & Observations Geothermal Heat Pump

Yet another VERY interested reader. I'm in SE Iowa, building a large shop/garage this spring.

I'm trying to decide among several options...

1. Install GEO (using pond or otherwise) for the house only and tie it in the note for the shed. Heat shed with in-slab radiant using propane water heater.

2. Install GEO for house and shop...is this even possible using one unit?

3. Forego GEO altogether...not likely, as I spent $2000 on propane this past fall, and while it's down a bit now, LP will probably climb back eventually.

Pond is about 150' from the house, so it's definitely doable. Just not sure how much experience local installers have with that type system...gotta talk to 'em about it, I guess.

My house is probably not too far from your location as we are south of Indianola. We heat and AC our house and garage (about 4000 sqft) with GEO. It was installed 2004 by LesMes based in Truro. They sized the unit and specified all the components such as pumps, thermostats, tubing, fittings etc. and installed it. My observation is that those guys understand the plumbing part pretty well but have only enough knowledge about the controls to make it work. After talking to other contactors I think that they are all like that.
At the end, after about one year of operation, I made several small changes to the "plumbing part", fixed few leaks and replaced the controls altogether.
Our heating electric bill in January was about $100.

Ladia,

Please share these changes and tweaks with the group, maybe we could all learn from your findings.

What was your average monthly heating bill before the changes were made? After?

First I measured temperature exiting from all ports of the heat accumulator in both heating and cooling mode. There was significant temperature difference between top and bottom discharge pipe in cooling mode. The cooling loop was originally connected to the same pipe as heating headers getting higher than desired temperature. After relocating the Toff to the bottom port (return to the HP) performance of the AC improved significantly.
The original control system provided only temperature control in 5 zones while the HP operation was controlled by temperature in the accumulator. Therefore the HP was needlesly running for about an hour or more/day even when there was not demand for heating or cooling.
Switching between heating, cooling or standby had to be done manually. It didn't provide temperature control of hot water that often overheated and popped overheat protection in water heater. When the weather got cooler and AC stopped operating there wasn't hot water until the protection was reset.
Therefore I bought small PLC (LG because it comes with programming software), 24V transformer, 10 relays, two dual temperature controllers, 1 60A contactor, terminal blocks etc and small cabinet. All together for about $500. The PLC has 24 discrete inputs and 16 discrete outputs.
All thermostats are connected to PLC inputs, all zone pumps and zone actuators, desuperheater pump, water heater, HP start request and reversing relay are connected to PLC output. One of the two loop temperature regulators controls heating and cooling temperature, one loop in the second controls HW heater temperature (desuperheater pump). The thermostats in the HW heater are set to lower temperature than the desuperheater loop therefore the electric heat is always turned off as long as the HP keeps the water hot or anytime when the HP is running. HP starts only when there is a demand for heating or cooling. Switching between cooling and heating mode is automatic. The PLC also controls recirculator of the hot water and turns all pumps on for 1 minute/day to prevent sticking. It also keeps track of number of starts and time running in each operating mode but I didn't analyze that part yet.
Beside relocation of chilled coolant for AC I added ports for possible future heat exchanger to heat HW solely by the HP and use electric heat just in the case HP fails.
Added ports and valves in the HW (desuperheater) loop used for descaling of the desuperheater heat exchanger. Added air trap consisting of 3 feet of vertical pipe Teed to suction of the outside loop pumps. The pipe has a valve in the top to let the trapped air out. It was needed only first few months of operation.

I also installed thermometers on every manifold and pressure gauges to outside and inside loops.

I would make just a guess that the total house electric bill decreased by 20 to 25 USD/motnh (about 10%). 10 USD comes from the heating and 15 USD from HW.

Wow. My brain hurts. What is a PLC?

Programmable Logic Controller. Think computerized super version of the old 24-hour on-off 110vac switch grandma used to fake being home while she was on vacation.

There is not a simple solution to complex problem. Geothermal heating is complex thus the control system is also, not necessary complicated, but complex. Leaking pond is not complex but the solution is complicated. Ask me about that one.

I don't know what I'm missing, but on my geo system I turn the thermostat up if I'm cold and down if I'm warm. Not really too complex.

Sounds like what I used to say Jersey... Until I got that first $700 heating bill. I have found that it pays to know the intricate workings of the system.

It is like modern cars. You start the engine and drive. That is not complex. Look under the hood. That is complex.

I believe that to get peak efficiency from a geo system, it must be understood, monitored, adjusted on an as needed basis. Many changing factors continually determine the adjustment frequency. Any of you who have paid an electric bill where the emergency heat strips were on more than they should have been will agree.

Since the heat pump can do more than heat/cool your house the control system should allow you to take advantage of it. Example:
The heat pump can heat HW four times cheaper than direct electric heat and heat it for free when AC is running. Therefore the control system should be smart enough to turn the direct heat ON only when the HP is not available due to failure, being turned off etc.
The main challenge is to match the HP and the controls to particular house. Ideally the HP should run continuously at extreme condition while still maintaining sufficient temperature inside the house. That is the American way designing it.
In the Europe they design it for about 70-80% load and then cover the deficit by direct heat. The thinking is that the peak load is required less than 10% of heating/cooling time while the HP, ground loop and total cost of installation is significantly less. Additionally the smaller HP cycles less.

When the system is new it should be mandatory to check not only if it meets expectation but if there is room for improvement in efficiency and/or comfort.
Example: Typical setting for floor heating temperature is 110 F. But I found that it works as well at 90F. While ago the HP run almost continuously for few days during very low temperatures and high wind. It was able to maintain only about 90F of liquid entering the floor because almost all loops were ON. But the temperature in the house was still maintained at the desired SP. Therefore I set the HP set point to 90F. Since efficiency of the HP is proportional to inverse of the temperature differential I expect that the lower temperaure rise will save some energy.

Wow Ladia...you are really up on this subject like a pro's pro!
-
...you better not turn out to be another one of Dwight's cats

Well my pond is leaking and the HP heat exchanger is in it. Will exchange geo advice for pond advice. I NEEEED POND HEEEELP.

Looks to be about $2,800+/- a year vs propane (so my 5 year payback should be close to target). This year has been cold, moreso last month, payback could be sooner as I'm sure I would have had larger LP bills than previous years. It will be intersting to do an overall analysis once I get the 5 years behind me.

Wow, if mine would have been that much more I would have been regretting putting geo in but of course we both know that meant something was wrong. It will be interesting to see once your sensor is repaired what you average down the road. d

Thank you, that was exactly the type of information that I was looking for. I'm following this thread closely, this is a facinating subject.

Propane, NG, heating oil etc are subject of swing in the price due to demand, speculation etc. Because the electricity generation and distribution is highly regulated (and is generated mostly from coal) it doesn't suffer unpredictable price swings.
Considering the cost of hydrocarbon fuels in the past several years my geo already paid for the difference in installation cost geo versus propane furnace. My cost was significantly higher due to installation of floor heating and air-conditioning.
We paid in average (and that is very rough estimate) about $70/ month for heating between December and January. Since the utility charges .041/kWh for the heating we have used about 1700 kWh/month. That is equivalent of about 58 therms, or about 41 gal/propane or about 5.8 million BTU. Heating the house by direct heat it would require about four times as much energy. We heat about 3700 sqft and the system was installed in fall of 2004.
I don’t do such calculations for living so, please, check the numbers before you take them as face value.

Now I don't have practical experience with a ground source heat pump, so with that disclaimer out of the way....
These systems should be less complex than a comparable air source system.
The driving force with these systems is using the heat stored in the ground vs air so there is less variation to deal with.
Right off the bat that means you don't need the energy robbing defrost cycle when the air temps are low. You are running an antifreeze solution through a closed circuit so you don't have to worry about the neighbor's cottonwood tree clogging up the outside heat exchanger.

The big variable with ground source is that the engineering and installation of the loop is critical as that is not pre-sized and tested by the manufacturer. However the tools and test equipment to evaluate the loop are common and inexpensive.

In a ducted system they are both equal in their complexity and unfortunately designers and installers have a pretty poor track record in executing this part of the system. The most efficient, magical box of engineering in the world can't overcome shoddy or poorly designed duct work. Again the tools for evaulating this part of the system "should" be standard kit with with a qualified contractor.

The accepted standard for sizing both air and ground source systems is called "Manual J". It works, but requires carefull and accurate input. Garbage in garbage will win in the end everytime.
Down here, in Texas, systems are usually sized for AC load. An oversized system can be worse than undersized as failure to control humidity has led to more than a few houses being dozed due to mold infestation. Variable speed and dual stage heat pumps can be a good way to deal with the extremes.

In the end there are fairly simple and objective methods to measure the systems perfomance and there should be a set of inputs the contractor used to size the system. It's a simple matter of comparing A to B.

The subjective areas are the inputs to the "Manual J". A certain margin of error is endimic here as the HVAC Co. can't be responsible for the building envelope.

I have tracked all my utility usage for the past years meticuously and know how much it changed year to year, what my averages were, etc. etc. Ladia is so correct about the swing and demand factors. Over 10 years I've watched swings in my own usage and utility prices. I have watched my LP prices go up over the years $1.10 in 2003 to $2.48 in 2007; thus, you can understand my decision to forego geo once we put the pond in; it wasn't if--it was when. I watched electric go from .0897 per kwa to .10/.11 2008. I would suggest anyone thinking of going geo to do their math based on their own situations.

The geo system can be simple or complex. Generally the forced air is about as complex as furnace.

Floor heating is another story altogether. Since there are many floor loops it is easy, if structured properly, to zone each room with own temperature control. The HP also heats HW so that loop also has to have a temperature control loop and has logic that disables direct heat when heat from HP is available. The heat/cool accumulator also has to have own temperature control. Then there is AC with its own temperature control and there is logic switching between heating/cooling. Because of large time constant of the floor heating (0.5 deg/hour) the mode of operation can't be changed forth and back like in forced air. My system uses high pressure AC that works very well but it makes whole house filter integration difficult. So there is logic in the system associated with that etc.



If you put the loop in the pond the biggest expense it the underground line from the house to the pond. So if in doubt add more coils in the water. It will increase the cost only marginally. Ground loop is another story. Over killing it will not improve or hurt the function but hurt you pocket.

My point which, I probably made poorly, is that the closed loop, ground source system setup properly should require less adjustment and maintenence that a comparable air source system.

Clearly any system can benifit from enhanced control and monitoring. No telling how many megawatts are wasted in this country because of dirty air filters or clogged evaporators on forced air systems. Variable speed blowers provide a means for a dehumidification cycle but few systems are being installed with the humidistat required to utilise this feature.

I could go on but the point being that there is nothing specific to the geothermal cycle that requires the consumer to be conversive in ladder logic to enjoy the benifits of these type systems. They are little different in their maintenence demands than the refrigerator purring away in the kitchen.

Multi-zoned, multi-staged or mixed systems are by their nature more complex be it geothermal, air source or a boiler system. The system designer and installing contractor are the keys.

I have to respectfully disagree about the complexity of the geo system. As a forcd-air system, it is really no different than a typical heat pump. It just exchanges heat in water instead of air, a much more efficient process.

One benefit of a geo system, as mentioned before, is it uses its waste heat to heat water. I do this process in a standard 80 gallon electric water heater, with the breaker turned off. This tank feeds another 80 gallon tank that takes over if needed, but at least it always receives water significantly warmer than it would directly from the well.

Now if you have radiant heat in your floor, especially in a concrete slab, you do need some fancier controls because of the thermal mass. This is a whole different topic.

Assuming geo with floor heating and AC.
Since each room has at least one but usually several floor loops it is easy to control temperature in every room (zone) separatelly. As opposed to natural gas, oil or propane furnace the heat pump can heat HW cheaper than direct heat. In fact it will heat HW for free by waste heat when AC is running. All this require temperature control for each loop.
So typical three bedroom house will have:
1.) Eight zones (kitchen, living room, bedrooms 1,2 and 3, garage, bathroom 1 and 2.
2.) AC temperature control (one for whole house or also zoned).
The zone thermostats for floor heating use different temperature algorithm than thermostats for forced air. The issue is a lag time between introducing the heat in the room and the temperature response. For forced air it is measured in minutes. For floor heating it is measured in hours. The thermostats are actually simpler because they are not programmable.
3.) HW temperature control with a logic that would enable direct heat when heat pump is not available.
4.) Heating/cooling accumulator with two heat and cool temperature control loops. The control loops control the temperature in the same vessel but have their respective sensors on different outlets.
5.) Logic switching between heating/cooling mode.
6.) Recirculation pump "excersise" function to spin all pumps for short time every day to prevent stiction. That is especially important for variable speed pumps set to low speed because they might not start after one season of inactivity.
I see the difference in the fact that for furnace forced air all the controls are more or less standard and built in the system. Just add a thermostat and you are ready to go. Geothermal with floor heating is designed according to specifics of particular house. I believe that purposely made programmable system for such application are already on the market making application of the geo and its efficient use easier.
When I built my house I was quite naive and thought that the guys installing it will install all the necessary equipment and proper controls. Only later on I learned that it wasn't necessarily the case. They made it work reasonably well and it was about it. So I built my own system. It was fun project but after the experience I would buy off the shelf controller and use it. Therefore I would strongly advise to avoid custom made systems based on a PLC and similar for most homeowners. The issue is maintenance and repair when something goes wrong. Most homeowners will be better off with off the shelf product that can be troubleshot by average HWAC tech. I built my own control system so I can fix but I doubt that average heat pump or HWAC tech could come to my house and deal with possible problems. Heck I have problems to fix program bugs etc sometimes.

Integrated of the shelf control systems are available from
http://www.tekmarcontrols.com/literature/a.html

Wow, Ladia. I missed your responses (several, along with others) over the past several days.

Now, I'm wondering if this is even something that I should attempt here (small town) with local vendors. When I first thought about this in '01, the ONLY outfit doing it within 35 miles didn't instill lots of confidence. The sold the HP and would install it...but (pre-pond) argued amongst themselves for a couple weeks as to how much tubing (digging & $$$) would even be required. I walked away...

I'm only 40 mins from Iowa City, so maybe there are others there I can talk to about this.

My shop will not be attached, but sit perhaps 50 feet from the house. It will have in slab radiant, I've installed it before, and will this time. Home has LP fired forced air...not sure how these 2 systems will (or even could) be tied together. Shop radiant can easily be supplied by 60 gal HWH, AC, perhaps just a window unit - I won't live in the thing!

...probably simpler to keep the systems separated.