Michigan Bosch Closed Loop - Questions and Issues (operating cost, pump failure, loop pressure)

Hi - this is my first post here - I apologize in advance for the lengthy post, but I want to ensure I give all the details. I could really use your help and advice. I am a "DIY" homeowner who is new to Geothermal. We had our home built in 2019 - 3250 sq ft in the metro-Detroit, MI area. House is well insulated - spray foam interior, 1" foam exterior. We keep the house at a constant 70*.

We've had some significant issues with our builder, and although his HVAC subcontractor seems like a good and knowledgeable guy, I can't help but have some skepticism when my gut is telling me something is wrong with our system. I'd like really like to learn so I am able to troubleshoot and potentially repair/maintain simple items going forward. I don't want to have a service call every time I feel something may be "off". I do plan on having another company come out to inspect it soon but want to have some base line understanding on things.

The system is Bosch SM060 on a horizontal closed loop system. Unfortunately, I don't know the length of the loop. From what I can tell, he did install the loops at a good depth - allegedly 6' and from what I saw, I believe it was at least 5' if not 6'. The flow center is a Geo-Flow, model 1333-1391, produced August 2018. It has 2 Grundfos pumps, UP26-116U. The installer used alcohol (methonal?) as antifreeze - I saw him fill the system with it in his flush cart. It should be noted, I am on a well and he filled with unsoftened well water.

I have 3 concerns I was hoping this community could help with:

1) We've always been disappointed with the cost to run this thing. I have nothing to compare it to, as this house was never on propane or natural gas. I have a reduced rate dedicated meter and panel for the geothermal. It literally only has the geothermal and the hot water heater on that entire 200 amp panel. I can share a detailed breakdown of run times and energy usage by month. Here's a brief breakdown of our last 6 months of costs and usage (costs are JUST for geo and hot water panel) - does this seem normal?

- Jan 2022: $424 / 3,137kw / 648 hours total heating run time, 3 hours on Aux heat
- Dec 2021: $270 / 2,021kw / 357 hours total heating run time, no Aux heat
- Nov 2021: $257 / 1,922kw / 260 hours total heating, 1 hour on Aux heat
- Oct 2021: $157 / 1,166kw /11 hours total heat, 61 hours total cooling
- Sep 2021: $157 / 997kw / 11 hours total heat, 88 hours total cooling
- Aug 2021: $281 / 1,800kw / 297 hours total cooling


2) One of the flow pumps seized. I noticed last month, in Dec - it was very hot to the touch. I pulled the bleeder screw and the rotor is totally locked up and not spinning. I tried to free it, but it's definitely locked up...bent the flat screwdriver trying to break it loose. Additionally there appears to be a lot of white "scale" on the outside of the working pump. Interestingly, I don't see this on the side of the non-working pump. I've attached a picture below- pump on the left is seized (and now disconnected), pump on the right is functioning and shows the white "scale". Is that anything to be very concerned with?

In retrospect I realize this was probably a major misjudgement, but I had disconnected the bad pump and noticed my lights don't dim nearly as much when the unit fires up with it disconnected. Reading a few older threads on here, I got the impression that these are fairly large pumps and some folks have found that running 1 or downsizing actually yields some operating savings. I think I've proven, via #1 above, that isn't the case for me. I'd like to replace it and it seems like something I can do myself. Is this as easy as turning the 2 way valves, unbolting the bad pump, and bolting in a new? I found the same pump online for just over $300 and can order and replace it if it's that straightforward. If it is, can anyone give me the step by step on which direction to turn the valves (they are on the sides of that flow center) to ensure I don't screw anything up?


3) I've had the ground loop topped off once before, by the original installer, sometime during the 1st year it was installed (2019). I recall him saying it was a little low (I had the impression it was marginal) and he topped it off while he was here - didn't indicate it was critically low. I wanted to be able to monitor it, so I bought a loop gooser and just checked it today. While running, on a 20* day here in MI, I am getting 8 PSI on one port (lower) and about 5 PSI on the other (upper). Also, the upper port had a thin layer of ice (frozen condensation) on it. I had to use pliers to loosen the cap to check the pressure because of the ice. To add - I have no expansion tank, just the piping to/from the unit with the flow center plumbed in. Low pressure concerns me greatly - I understand pressures can vary depending on the time of the year, but should it drop this low or does this indicate a leak? Should I boost this up right now with the gooser? My concern there is, aren't I slowly diluting the concentration of antifreeze in the system each time I add?

Thanks in advance - I'm hoping with this forum's help I will learn more and become more comfortable and capable with my Geo system.

 

have to run but some quick feedback
1) electric consumption looks pretty normal to me. hook up propane to your house for a year and report back what that costs

2)I don't have one, but I think the UP26-116U is widely ridiculed for being overly power hungry for not much increase in flow over the version with 99 in the model number. do some searches on this forum and you are bound to find some threads on it. Its hard to comment on whether or not you actually need two 116 pumps but you could get some tools and try to figure out flow rates you have with one of them running. not sure if the 116 has this but I remember the 99 allowed you to set one of three speeds so you could actually dial in the speed more appropriate for your loop setup. heat pumps need 3gpm/ton. I think you have a 5 ton unit there so you need to flow 15gpm (really only in stage 2 when working hardest but no way to dial it back when heat pump is in stage 1). Reducing pumping to what you truly need would be one way to make you system more efficient and get the electric consumption down (somewhat don't expect miracles/50% drop). haven't replaced one but I think what you posted is accurate - turn valve to isolate pump from loop, extract pump and reverse for new pump (generally I'm sure there is a more detailed version out there). the wite stuff you see if probably dissolved salts in the loop water that deposited when your pump burned up evaporating some water leaving salts behind. not sure straight well water was the best for your loop but I probably wouldn't worry about it unless some other water/loop based failure happens in quick succession
3) you want positive pressure in your closed loop with that setup. you are showing positive pressure so not sure if there is anything to worry about. pressures vary with season - geoflo (maker of your flow center) has a nice "white paper" on loop pressures here: https://www.geo-flo.com/presentations-and-tech-documents/

 

First, thank you for you replies!

Bummer - I've heard that from both companies that I have had out here over the 3 years (installer and I did have one other independent company come out) - I'd be crying harder if I were on propane.

I'm currently trying to research, but is there a way to check/calculate based on actual installed equipment what my flow requirements are? Everything I am reading shows folks calculating off known piping sizes and loop lengths. Unfortunately, I don't have this information. If it'd help optimize the system and long-term operating costs, I'd absolutely consider swapping over to one or dual 99U pumps.

Thanks, currently trying to read through the various materials. Everything I had seen thus far (and what I recall being told, but I could be off) is that something like 30-40 PSI is optimal. Would having lower pressures like I currently do degrade performance/efficiency?

 

I am probably wrong in this and it's a fairly rudimentary analysis, but doesn't this indicate that something is wrong, as it seems like propane would have been much cheaper? I'm not saying Geo isn't more efficient or cost effective, but I am not seeing it on my end - indicating something isn't right with my setup.

The following example is using actual January 2022 usage:

Geothermal (and hot water tank) consumption: 3,137kW
I found a conversion of 3412.14163312794kW per BTU
I found another conversion of 91,500BTUs per gallon of propane

As such, 3,137Kw consumption is 10,699,299 BTUs.

10,699,299 BTUs is 116.93 gallons of propane.

Let's assume even an 80% efficiency furnace, I'd need 146 gallons of propane.

Propane in my area is currently $2.40/gallon. Let's be conservative and say I am paying $2.50/gallon:

146 gallons at $2.50/gallon is $365.

My electric bill for just geothermal and hot water was $424.

Wouldn't I have been $60 cheaper heating with propane?

 

You're missing a major factor in your analysis. All heat pumps are greater than 100% efficient. A properly installed geothermal heat pump should be about 350% efficient.

This means you are getting ~3.5 times the heat output than what you calculated. So, your equivalent propane bill would have been 3.5 X 365 = $1,277.

You saved 67% on your heating costs by using geo instead of propane.

 

That august data seems suspect. 1800 kWh to cool? What you keeping the house at in the summer?

The other numbers don’t seem that crazy. I have a well insulated/air sealed 2,400 sq ft home with a 4 ton unit. My usage in August was 770 kWh, but we keep the house at 75 *F.

For January we were at 1,840 kWh to heat, keeping the house at 68 *F.

I’m located in SE CT for reference, so probably milder weather.

 

It looks like Sensi doesn't log avg temp so I guess I can't say definitively. On heat, we keep it at at constant 70*. With A/C, we usually bump that up to about 76*


Thanks for the discussion everyone - like I mentioned, just trying to learn and optimize if at all possible.



Would anyone be able to point me in the right direction on how to calculate a proper pump sizing? I don't know the field length or specs. Can I calculate based off incoming and outgoing pressure differentials or anything?

 

you need to do a manual J calc to size the system correctly. It will determine your heat loss/gain. Search cool calc in google and a free website will come up that will help you perform the manual J. It will take some effort to perform, but more time consuming than difficult. From there, compare your heat loss/gain calculated to determine if the HO is sized correctly.

For the loop, you can use loop link rlc to calculate the size of the loop and figure if it’s sized correctly.

 

you don't say how your hot water is being produced - assuming electric resistance or heat pump hot water heater? do you have a desuperheater in the geo unit? all of those things can influence electric use and depending on configuration might explain the higher electric use in August. For instance, say you have a desuperheater and electric tank water heater. During winter months, the desuperheater is likely to create nearly all of your hot water and it won't create any in the summer months. So if you had an electric hot water heater, it would be cranking in August possibly skewing the electric meter data (ie geo goes down but hot water heater goes up).

If you don't have a flow measuring meter installed on the ground loop (most don't), you can get the ground loop flow rate by measuring the pressure drop across the geo unit's heat exchanger with the flow center running. With the pressure drop, you go to the unit's performance data chart (find online) and that will tell you what the flow rate is. You will have to correct for antifreeze concentration to get the right flow rate. Pressure drop is measured using needle like tools inserted into your Pete's Plugs. I'm assuming you have those since you indicated your geo contractor added water to the ground loop in #3 of the original post?

 

I think he is talking about sizing of the loop pump not the geo unit's size (which is what the manual J would be for). If he had all of the loop configuration, then sure he could use loop link RLC but he indicates he doesn't know any of the ground loop info. So measuring the system in use (via the Pete's ports) are really the only viable way (or dig up the lawn).

 

thanks for the correction. I didn’t read it close enough. On second read, now see he was looking for pump information.

agree the easiest solution is to pull pressure differential from the PT ports and calculate the flow rate than compare that to the manual.

 

Thanks everyone - to explain further:

I have electric hot water, on the same electrical panel as my geothermal. I do have a desuperheater, with a separate (unpowered) hot water tank as a holding tank for it.

I do have a pressure gauge (loop gooser I recently purchased) and have the PT ports on the geo loop. I'll take measurements to confirm but from what I had seen earlier this week, with the unit running, it was a 3 psi differential. Both were low (I think this is considered too low anyway) on pressure - 8 psi on one, 5 psi on the other. Being that it's a new pressure gauge, I can also find a way to validate that it's reading pressure properly.

Should I add some water to up the pressure? I had seen online that ~40psi running pressure in winter is acceptable. Is it advisable to increase to that?

 

Do you have a hybrid water tank or a regular resistance heat hot water tank?

Your setup, with a buffer tank, is similar to mine. I have a 40 galling buffer tank with an 80 gallon hybrid hot water tank.

Are you sure your desuperheater is on? My contractor forgot to turn mine on (was just a switch on the side of the control panel), but luckily I noticed it pretty early.

Those pressure drop numbers seem low, but I believe you want to have the heat pump running for a bit when you take them and have the desuperheater off.

There’s another recent thread (titled something like 89 degree air too low) where someone posted an article with how to measure pressure drop correctly.

 

I think this is the performance data for your unit but confirm: http://www.millpondmech.net/uploads/3/4/4/8/34482690/sub-sm_rev_c_engineering_submittal_06.2021.pdf You need the performance data to understand your unit and the measurements you are getting plus it will probably answer some of your questions too

I didn't see desuperheater production in the performance data I linked to but generally, during summer months when in cooling, desuperheater probably won't run until the incoming water temp is more than 60 deg. In heating, the desuperheater will probably produce hot water at virtually all incoming water temps. Even though it might produce some hot water during the summer, it will be a fraction of the amount produced during the winter (like 25 to 50%). So, your electric resistance hot water heater is going to run alot during the summer and probably never during the winter. this is what I was outlining in post 10 above and is likely the reason your August energy use seems skewed. Heat pump hot water heater would bring down the electric use in the summer but I wouldn't go doing that upgrade until your current electric hot water heater needs replacing.

the performance data I linked shows pressure drop for various incoming water temps but I didn't see one for 30deg range. regardless 3psi pressure drops looks like you probably have 8 or 9 gpm which is fine for your stage 1 but not for stage 2. So you probably do need two pumps. My guess is the second pump could be the 99 unit (to work with the 116 you currently have) or both pumps could be 99s. again, althoguh these are single speed pumps, I think you can set one of three speeds to better dial in the total flow. Others will be able to comment on this better than me.

I would refer to that white paper I linked prior regarding loop pressures. With your system, you need positive pressure across all seasons. My recollection was positive pressure is a mixture of fluid expansion/contraction as well as the ground loop pipe expansion and contraction and that greatest positive pressure was actually during the winter and not summer but that paper better explains it more than I can do in a few sentences.

 

Thank you all so much for the additional info!

- I have a regular old Bradford White 2-element water heater
- I actually did have the desuperheater off. I forget when (sometime in Q3/early Q4) or why I turned it off, but it's been off for a few months. The installer drilled the fear of God into me to never ever leave that switch on if I am killing the well pump or draining the hot water tank as even a few seconds with no water will fry the desuperheater pump.
- You actually brought something to light that was described improperly to me. When the unit was installed, I was told by the builder (not the installer) that the desuperheater effectively allowed me to have almost free hot water in the summer, as the unit would first dump the heat to the buffer tank during the cooling cycle. He further told me that in the winter, it doesn't help nearly as much. A quick Google search showed me that this isn't accurate. Desuperheater is back on!

Lastly, I sincerely appreciate the additional information regarding pressure drops and flow rates. I will sit down this weekend when I have a few quiet mins to read through it all and start assessing my system.

Again, thank you all so much!!!!

 

Its a common misconception people make with the desuperheater and when its useful. I don't know why when data tables show the opposite. I broadly outlined what my waterfurnace unit does and I fully expect your bosch unit to follow the same pattern if not function identically because there wasn't desuperheater performance listed in the bosch manual I linked. Why this is the case has to do with the refrigeration cycle and the various temperatures of the gases/fluids in the cycle but I haven't really studied it in depth.

 

My water furnace series 5 with desuperheater makes hotter water in the winter vs the summer.

 

FYI, the pressure in a pressurized loop is to ensure no negative pressure occurs when pumping. A vacuum can cause pump failure due to cavitation and is bad for pipe connections.

Also, a desuperheater is just a small heat exchanger before the reversing valve. It will lower the effective output to the house during heating mode, and will increase it during cooling mode when being used. It is best left on under most conditions.