Ground water heat pump + natural gas

TekWarrenFebruary 4, 2014

Long time reader but just registered for some help on my specific home HVAC setup.

Recently purchased a new home that is around 15-16 years old. The house had some sort of energy audit by the previous owner and he had extra insulation and some other things done.

The HVAC consists of a Goodman 95% efficient nat gas furnace as well as a ground water source heat pump (can't recall the brand at the moment). I'm fairly certain there are no electric heating strips used. When the thermostat is set emergency mode, the nat gas furnace kicks on.

Throughout this whole last year even after having everything check out last year I'm still left wondering how best to use this system. The previous owner said he ran in EM mode all winter (Michigan) and stated he figured it to be cheaper (?). Maybe offset electric costs? I ran mostly using the heat pump last winter, after having it checked out. This winter I am running EM mode just natural gas trying determine differences. I have a rising electric bill (instead of going down!) and now a gas bill on top of it all. I know electric usage is relative my family's habits but I tell you I am pretty anal about shutting things off when not in use, even minimal lighting at night!

This winter and last I run a constant temp all the time, whatever feels comfortable to us. This year it's been at 67 day and night. The blower runs 24/7 which concerns me but the temp seems to remain rock solid. I don't think the blower is stuck on as I can turn the temp down and the blower will turn off. I'm assuming the blower is maintaining more constant temps throughout the house but I don't know if it is adding to my electric bill (versus turning on and off with the furnace). Filters are change religiously.

If I go back to "normal" mode on the stat using the ground water source pump as the primary can I efficiently utilize set back temps? Everything I read says set it at one temp and leave it. But I wish I could somehow get a better balance of the two heat sources I have available to me or at least use them most efficiently. My wife and I are out of the house ~10hrs a day during the week so that is a lot of time for a possible setback temp but I'm not sure how much is safe or cost effective.

I have a lot of questions I don't even know how to ask still. I specifically asked the HVAC tech ahead of time I wanted familiarization but I didn't get much. I know he did some maintenance a year ago and repeatedly mentioned how good things looked when he cleaned them. A pressure meter was installed that has a floating bead to show active water pressure. He also did something with the fan wiring I think to increase it or something...not quite sure.

I keep wondering if I need a better tstat to handle these two types of heat sources? I would assume that it is ok to handle them since the previous owner was not the kind of guy to skimp or do things half-.... I looked up a bunch of info on it and can't remember the model honeywell it is at the moment.

Thanks to all who take the time to read and comment on this long post! Any input is GREATLY appreciated!

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You have a geothermal heat pump and a 95% efficiency gas furnace? If that is true, then I agree the previous owner did not skimp on the HVAC equipment.

What are your current gas and electric rates? This will help determine which fuel is cheaper to operate.

What are your annual heating costs? If find it curious you have the two most economical systems to heat a house yet you set the thermostat to 67 degrees. Do you like it that cold in the winter?

Depending on the blower you have, running it 24/7 will use a lot of electricity. You should let the fan operate in auto mode and save a lot of money.

Don't assume anything about your thermostat. I have read about the most expensive systems being installed with an inappropriate thermostat. Post the model number for comments.

    Bookmark   February 4, 2014 at 10:48AM
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Now your asking me to do math which an IT guy should be able to do but this one sucks at it LOL. I need to dig into it more but I'm thinking the electric rates would be lower. I think I can look and see what last years electric usage was, we have a smart meter now but not sure how far it goes back. I don't remember electric going as high as it is now, and I was using just the geo thermal then. Nat gas bills where next to nothing last year, but do have hot water heater, dryer, I think that its it on gas when not using furnace.

The temp is based on comfort level honestly. Its just my wife and I. I could go warmer but it just isn't necessary and I am cold wuss by nature.

The blower has always been in auto mode, I've checked it multiple times throughout the year and even switch to on and auto again. It will spin down, or it did the last time I checked it if I drop the temp. I'm just wondering if the tstat keeps the circulation going constant in order to kick the furnace on less? We do have a finished basement so in the summer constant circulation may be beneficial(?) but in the winter I'm not so sure. I don't need the basement heated necessarily. There are a good number of returns, a larger one in each level and main level in each bedroom, I keep all the doors open.

-I will get the model info tonight and reply with that. I didn't know if there might be more "advanced" tstats available now that might better handle my equipment. When playing with things last year I did find that the nat gas will kick on if I increased the temp quite a bit (not sure how many degrees) while running in normal mode with the geo-thermal as the primary.

Even with my zero knowledge of HVAC it seemed odd to me as well to have a 95% gas furnace on top of a ground water heat pump... And to top it off "they" found the gas more efficient. Both have met our needs in terms of heating so far between this winter and last.

Thank you for your time.

    Bookmark   February 4, 2014 at 11:34AM
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Natural gas prices are low right now. I suspect it costs less to heat your house with the gas furnace. The rates will determine if this is true or not.

I am not sure what your thermostat is doing with respect to the blower. Do you have a humidifier? If yes, it may be turning on the blower to circulate the air through the humidifier.

    Bookmark   February 4, 2014 at 11:40AM
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No humidifier. The furnace, or some function of it actually removes moisture from the air. There is a pump...device that shoots water through a hose from the furnace equipment to the sump drainage. It is not constant and not a lot when it happens. I suspect to keep the basement dry.

    Bookmark   February 4, 2014 at 12:01PM
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What you are describing is a condensate pump. The furnace produces the condensate and flow outs out into the pump. This is pumped over to the sump. I have the same configuration in my house. The blower should not be turning on when this occurs.

    Bookmark   February 4, 2014 at 12:20PM
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I'm really throwing myself for a loop here... Studying the graphs more I guess i'm only using slightly more electricity for last month compared to a year ago. And actually a bit less gas! I know the first part of the winter I used nat gas last year before I had the geo thermal checked out but I am sure I was using geo in January...maybe not. I may be making a bigger deal out of the costs part of this than it is.

    Bookmark   February 4, 2014 at 12:21PM
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I will have to try to watch/listen when the excess water is pumped away to see if the blower is running at that time. I think I have become used the the air sound/movement so that it is not as noticeable, that and I am always down in the basement when the water is being moved so I will check for this.

    Bookmark   February 4, 2014 at 12:25PM
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The model of my tstat is a Honeywell FocusPRO TH6000 Series.

I actually emailed the previous owner and he was kind enough to call me last night. It sounds like his reasoning for using the natural gas over the geo thermal is that one year the pump went out. I didn't get (nor am i knowledgeable enough to assume) if this was the actual well pump or a pump in the geo thermal unit. I'm thinking the well pump feeds the geo thermal. There is also underground sprinkling and he said he ran it every day for 5-6hrs (several zones, large yard) so he was working that pump pretty good. I am not running the sprinkling anywhere near as much. So it almost sounded like that scared him away from burning out another pump as well extending the life of the geo by only using it for cooling.

He did have it all figured out cost wise and said it was costing just over $800 a year in gas...but prices fluctuate.

Still debating if I should go back to using the geo but use setbacks, the nat gas will kick in to accomodate for larger drops but will this wear the system?

I did test the tstat again last night by dropping the temp and the blower will stop if I drop it several degrees. I set it to drop to 65 at night and during the hours we are away at work but that is only 2 degree drop so I'm not sure how much difference it will make but it will prevent the blower from running 24/7. Should I have a larger drop? I wouldn't go below 65 I would up the "at home" temp if anything.

Also any thoughts using geo as primary (the way the stat would normally operate) and using setbacks? Seems like I always read that setbacks are not good with geo but in my case the backup source is not electric strips but the nat gas.

Thanks for any help.

    Bookmark   February 5, 2014 at 9:45AM
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You should have separate pumps for the geothermal and "underground sprinkling". I'm a bit surprised that the well serves multiple purposes. I thought geothermal required it's own dedicated well or else you experience the problem of the water being depleted like happened here.

    Bookmark   February 5, 2014 at 2:30PM
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I could be wrong (likely) I am really not knowledgeable in this area...for that matter the previous owner may not be either and was rambling a lot. It *sounded* liked he thought whatever pump went out was due to excessive use and he mentioned the sprinklers. I don't know that water was actually depleted from the well, sounded like just a pump failed or overworked.

I guess what I'm trying to get out of this is if I can use my geo thermal with setbacks, assuming the nat gas will kick in when necessary (it will I have obvserved this) OR if I should just use the nat gas furnace at 95% efficiency.

If the geo is more efficient I don't want to not use it based on the worry of the previous owner that the pump will fail again. If it does, I of course have the gas furnace as unfortunate as it would be to have a failure I still have another option. If the geo did somehow in fact lead to the failure of the main well pump, then I would reconsider. I think from my digging and trying get info for insurance purposes, that my geo is open-loop so that water may in fact come from the main well right?

    Bookmark   February 5, 2014 at 3:11PM
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You touch upon an issue that is sometimes overlooked. If your energy costs are identical for the gas heat and heating with the ground source heat pump, you are better off using the gas furnace since you will have less wear on the more expensive equipment.

If the energy cost is different, you get into some slightly more challenging calculations. In order to make the best comparison, you need to know the life time and repair costs for your equipment.

    Bookmark   February 5, 2014 at 3:33PM
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That makes a lot sense, and may be what the previous owner found and was trying to tell me. He specifically mentioned prolonging the life of the geo by using just for cooling in the summer. The furnace appears to be fairly new and the geo "unit/pump?" which sits in the same utility room is fairly small and looks a bit older, perhaps originally installed with the house (1997). He left me with a good bit of records so I might be able to verify that.

Maybe for now I just run the gas and program a few degrees of set back temp during the day?

    Bookmark   February 5, 2014 at 3:47PM
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I am a proponent of large setbacks. When no one is in my house daytime durning work week, there is generally no HVAC running. Sometimes in shoulder seasons, the dehumidifier is running because I live in a very humid climate.

    Bookmark   February 5, 2014 at 4:27PM
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There is no harm is having a large set back with a gas furnace. I use a set back of 71 to 64 degrees at night. The temperature rarely ever gets down to 64 degrees, but even if it did there would be no harm.

I was hoping one of the geothermal guys would comment on your set up. My gut tells me the geothermal system has some issues. You should have it serviced in the spring so you can keep cool in the summer.

    Bookmark   February 5, 2014 at 4:59PM
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Assuming that gas is the way to heat, It would be good to have an expert's guidance on how much inactivity is good for the ground-source system. Even if it is not to be used for heating, it is possible that it should be turned on and run in that mode during cool weather periodically to keep the system in good shape.

I used to run night time set-backs into the 50s at night and to 50 during the day when I lived in cold climes. I don't mind, even like, sleeping in cool conditions. I do, however, like it warm when it is time to get up.

I moved a pretty good Honeywell, set-back thermostat 5 times before Katrina finally killed it. It was used on gas heat-only, oil heat-only, and then on three gas heat/cooling systems. Four of them were in houses that I was renting.

    Bookmark   February 5, 2014 at 6:11PM
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First of all what make/model geothermal heat pump do you have? Do you have an ‘As Built Book’ that should be in the mechanical room detailing the design of the ENTIRE system and ALL initial measurements at start up when things were (supposedly) running right?

What ARE the correct details of your ground heat exchange system? How many and how deep are the boreholes, if vertical? Is it open loop? If so, how deep is your well? Is your gas furnace a single speed blower or variable speed?

If your system is open loop, a big factor affecting efficiency would be the depth of the well and the power required to pump the water up from a deep well as this is not a closed, balanced system as any closed loop system is, pressure of water pumped up equals pressure of water being pumped down, more or less, like an elevator with counter weights to balance out the load.

Some things just don’t add up. You mention an ‘under ground sprinkler’. If this is part of your geothermal system then it is known as a ‘soaker hose’ and while sometimes installed in vertical borehole systems, it is more common for horizontal loops that are more likely to be affected by extended periods of dry weather. Its purpose in horizontal loops is to rehydrate the ground and increase conductivity with the geothermal piping. Horizontal loops may also be more prone to areas with voids between the soil and the ground loops during extended periods of dry weather. This is less of a problem with vertical boreholes as they’re more likely to pass through the undisturbed overburden into solid rock and hopefully fissures with water passing by.

Sounds like the previous owner installed a GREAT system. What does this meter with a float actually measure, feet of head, PSIG, or GPM? Is it made by Blue-White or Dwyer? What does it say exactly when the system is running?

I’m not a big believer in set backs with heat pumps. Even a basic T-stat can do a good job. You can experiment to get an understanding of how things work. However, my own experience with our own geothermal set up is to 'set it & forget it', don’t ‘micro-manage’ the system and just let it do its thing. I KNOW our system runs more efficiently when I leave it the hell alone (which I often won’t) - and I’m supposed to be the expert!

Regarding the reliability of the geothermal system, it should be able to run for YEARS without any problems. Don’t be afraid to use it!



    Bookmark   February 6, 2014 at 1:51AM
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I'll try to answer some things as best I can and comment on all these items (appreciate all the input!)

I had everything checked out/cleaned last year, there are no functionality issues that I can tell. I used gas for part of the winter last year and also the geo, both heated just fine, geo also cools just fine. It just worried me that the previous owner used the gas rather than the geo when I had assumed geo is so much more efficient.

He ran the tstat in EM mode to force gas only (which is what I am doing now). I would like to use the geo if it makes sense to.

Is it safe for the equipment to run geo with a setback? Maybe a large enough setback that the gas does the leg work in order bring the initial temp back up, then the geo maintains?

The home is very well built and sealed, energy audit was done and insulation in key areas was added. The previous owner did all this and left me with a packet of info on all of it.

The geo is a Bard, I'll have to double check the model. I know nothing about how the loops are run and honestly I'm still not 100% on the open vs closed. I will ask the previous owner who installed the geo therm unit and maybe I can get some answers. There is a manual about the unit but I don't recall seeing much more than that regarding the loops and such.

Fairly certain the blower is variable. When I have the temp the same 24/7 it it is constantly moving air but at pretty low even speed.

The sprinkling may be an unnecessary variable I/he threw in here. It is not part of the geo system as far as I know. Previous owner mentioned the lawn sprinkler system and that he watered every day for 5-6hrs (large yard) and that this may have led to whatever pump went out that he had to replace. The way he explained it made me think that the main well was feeding the sprinklers, geo, house, everything and the figured he had overworked it or something. Maybe this isn't how it works and these things all have their own pumps.

The meter the tech installed last year I think shows PSI and when I have pulled the ring to make it show a reading it always between 5 and 6, normally around 6. I think this is good?

I'm trying to understand why the owner would install a nice new nat gas furnace on top of the geo but I think it all goes back to whatever pump failed and him thinking that it would put less stress on it. -I'm glad to have to have options! But wondering how/if/should I try to figure out a way to utilize both? Smarter tstat?

I know there are a lot of holes here and I apologize for that.

    Bookmark   February 6, 2014 at 11:16AM
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