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Thread: "Charging" Geothermal Field

  1. #1
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    "Charging" Geothermal Field

    I'm doing the controls on a geothermal upgrade project that we've just completed. This was the replacement of 25 year old heat pumps and associated mechanical equipment on an original 90s geothermal system that was installed when the building was built. The system has not run well for years due to failed compressors, etc in the old units. Now that the upgrade is complete, we're finding that when too many zones are heating at once the geo loop temperature falls faster than the field can keep up. There's only 5 heat pumps on the system but they're each 15 to 20 tons so the load can be significant if they all run at once.

    The mechanical consultant is suggesting the issue may be due to the fact that the HVAC was not operating this summer during the project/construction and therefore the field has not been "charged" with heat through the summer months.

    On all the past geo projects I've worked on (admittedly not that many) we were typically expecting a sort of constant geo field temperature year round, I had not previously heard of this concept of "charging" the field in one season to be ready for the next season. It seems to me that this could be an issue also if say you had a mild summer and then a cold winter. This building has never had any backup or supplemental heating system in the past.

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    It sounds like the field is too small for the load. Was the field size documented when it was installed?

    It is true that up to a point, the earth is used to store the heat during the summer. But it has limits. That is the reason geo manufacturers specify that the system must not be used during construction. The load is higher because the house isn't complete so the heat in the field is depleted during November and December (for example.) Then the occupants move in and find that the system is using auxiliary heat during January and February. WaterFurnace's policy is that they will not honor warranty if the equipment was used during construction.
    AOP Rules: Rules For Equipment Owners.

    Free online load calculator: http://www.loadcalc.net/


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  4. #3
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    Quote Originally Posted by zzip7 View Post
    I'm doing the controls on a geothermal upgrade project that we've just completed. This was the replacement of 25 year old heat pumps and associated mechanical equipment on an original 90s geothermal system that was installed when the building was built. The system has not run well for years due to failed compressors, etc in the old units. Now that the upgrade is complete, we're finding that when too many zones are heating at once the geo loop temperature falls faster than the field can keep up. There's only 5 heat pumps on the system but they're each 15 to 20 tons so the load can be significant if they all run at once.

    The mechanical consultant is suggesting the issue may be due to the fact that the HVAC was not operating this summer during the project/construction and therefore the field has not been "charged" with heat through the summer months.

    On all the past geo projects I've worked on (admittedly not that many) we were typically expecting a sort of constant geo field temperature year round, I had not previously heard of this concept of "charging" the field in one season to be ready for the next season. It seems to me that this could be an issue also if say you had a mild summer and then a cold winter. This building has never had any backup or supplemental heating system in the past.
    B S
    Sounds more like that "Mechanical Consultant" is trying to cover his own BUTT! How much warmer does he say the ground will be? 5, 10, 20F. The field should never change more then a few degrees up or down, any more and its not large enough.

    Any #'s on the field temperature under the old system?

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    Quote Originally Posted by pecmsg View Post
    B S
    Sounds more like that "Mechanical Consultant" is trying to cover his own BUTT! How much warmer does he say the ground will be? 5, 10, 20F. The field should never change more then a few degrees up or down, any more and its not large enough.

    Any #'s on the field temperature under the old system?
    Yeah this is what I thought. There is was some talk of getting me to program the controls to prevent more than 2 of the 5 heat pumps from running at once, but that doesn't really seem like it's going to be a real solution. I suggested that they need to consider adding more supplemental heat because I also think the geo field is undersized. I don't have the old temperatures though.

    But right now, with no heat pumps running, the temperature levels off around 15C (59F). When all the units run, it drops to around 2C (35F) within about 15 minutes and then all the units trip on low pressure.

    The consultant said he expected a geo temperature of ~30C (86F), but I can't say I've ever seen a geo system that warm in the winter. So I don't see how we can "charge" the field with that much heat.

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    Quote Originally Posted by zzip7 View Post
    Yeah this is what I thought. There is was some talk of getting me to program the controls to prevent more than 2 of the 5 heat pumps from running at once, but that doesn't really seem like it's going to be a real solution. I suggested that they need to consider adding more supplemental heat because I also think the geo field is undersized. I don't have the old temperatures though.

    But right now, with no heat pumps running, the temperature levels off around 15C (59F). When all the units run, it drops to around 2C (35F) within about 15 minutes and then all the units trip on low pressure.

    The consultant said he expected a geo temperature of ~30C (86F), but I can't say I've ever seen a geo system that warm in the winter. So I don't see how we can "charge" the field with that much heat.
    86F that's 30 higher then ground temp. Ask him how the A/C's are suppose to operate with that incoming water?

    Bring units on 1 at a time, when the temp begins to drop continually you know how many units can operate at a time.

    How much is this clown getting? Get 10% for doing HIS job!

  7. #6
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    If the loop has antifreeze/water mixture, all the equipment I've dealt with allows operation down to 15F.
    AOP Rules: Rules For Equipment Owners.

    Free online load calculator: http://www.loadcalc.net/


    There = not here. Their = possessive pronoun. They're = they are
    It's = contraction of it is. Its = the possessive form of it
    Too = also. To = expressing motion. Two = 2
    Then = after that, next. Than = indicates a comparison.
    Questions should end with a question mark "?" Statements end with a period "."

  8. #7
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    Quote Originally Posted by kdean1 View Post
    If the loop has antifreeze/water mixture, all the equipment I've dealt with allows operation down to 15F.
    There is glycol in the system, but the units see a ~20F deltaT across their coils. So I think the issue is that when the loop supply temp gets down around 35F or less the temp is around 15F by the time it leaves the unit which is around the trip point on these units.

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    Quote Originally Posted by pecmsg View Post
    Bring units on 1 at a time, when the temp begins to drop continually you know how many units can operate at a time.
    That's what I have done for now while they go back to the drawing board on this, because people are freezing in the building. I am only able to run 2 continuously, but this doesn't work as due to the size of some these spaces and the amount of glass they need to run most of the time to keep the space temp up. So if we actually want to maintain the space temp in the building we're going to end up having all the units running at once on a cold day.

  10. #9
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    Simple logic would seem to indicate that with a heat sink as large as a planet - any heat added or subtracted to it by a comfort cooling system is only going to have a small effect and very localized impact. I don't depute that there is Some heating-the-field effect to be had in cooling season - but I can't imagine that it could last more than a few weeks. And I would think that any "charging" of heat would have primarily come from the summer sun heating the ground (which provides about 300 BTU's per square foot) rather than from the cooling system rejecting heat to the ground.

    By the consultant's logic you could let a building 'charge' with heat sitting in the sun all summer and then have that store of heat 'saved up' for use all winter.

    If you have the correct fluid and the correct flow - your 'heat exchanger' is very likely to be too small. <g>

    Has it been very dry where you are? Lengthy rainfall shortage? Drought? I have often wondered if a field loop works measurably better in wet soil than in dry soil - due to greater heat exchange efficiency. Has the building been added to over the 25 years? Any other changes to it? Color? Wall/roof materials?

    Based on your description it seems like they have to either add field loops or wells - or supplement the building loop with an additional source of heat. <g>. But let's start with "if it worked 25 years ago - why doesn't it work now? With answering the first "IF" first being the correct starting-point. <g>


    PHM
    ----------


    Quote Originally Posted by zzip7 View Post
    I'm doing the controls on a geothermal upgrade project that we've just completed. This was the replacement of 25 year old heat pumps and associated mechanical equipment on an original 90s geothermal system that was installed when the building was built. The system has not run well for years due to failed compressors, etc in the old units. Now that the upgrade is complete, we're finding that when too many zones are heating at once the geo loop temperature falls faster than the field can keep up. There's only 5 heat pumps on the system but they're each 15 to 20 tons so the load can be significant if they all run at once.

    The mechanical consultant is suggesting the issue may be due to the fact that the HVAC was not operating this summer during the project/construction and therefore the field has not been "charged" with heat through the summer months.

    On all the past geo projects I've worked on (admittedly not that many) we were typically expecting a sort of constant geo field temperature year round, I had not previously heard of this concept of "charging" the field in one season to be ready for the next season. It seems to me that this could be an issue also if say you had a mild summer and then a cold winter. This building has never had any backup or supplemental heating system in the past.
    PHM
    --------
    The conventional view serves to protect us from the painful job of Thinking

  11. #10
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    So he charges the ground, but it doesn’t dissipate in to the earth away from the tube?
    Isn’t that the point of geo?
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

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    Quote Originally Posted by Poodle Head Mikey View Post
    If you have the correct fluid and the correct flow - your 'heat exchanger' is very likely to be too small. <g>

    Has it been very dry where you are? Lengthy rainfall shortage? Drought? I have often wondered if a field loop works measurably better in wet soil than in dry soil - due to greater heat exchange efficiency. Has the building been added to over the 25 years? Any other changes to it? Color? Wall/roof materials?
    There haven't been any real changes in the building configuration or layout since it was build. It's a municipal rec centre with a large gymnasium, fitness centre, and a small admin office area. The weather this year has been pretty typical for the area, normal summer, and so far pretty normal fall. Lots of rain as we always get here on the Canadian west coast.

    You comment about a heat exchanger made made me think though. The original system had the building loop directly piped with the geo field system in a primary/secondary configuration. The new piping arrangement has a heat exchanger between the geo field and the building loop... Wonder if that heat exchanger is under sized for peak load.

  13. #12
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    Time to check the approach? <g>


    Quote Originally Posted by zzip7 View Post
    There haven't been any real changes in the building configuration or layout since it was build. It's a municipal rec centre with a large gymnasium, fitness centre, and a small admin office area. The weather this year has been pretty typical for the area, normal summer, and so far pretty normal fall. Lots of rain as we always get here on the Canadian west coast.

    You comment about a heat exchanger made made me think though. The original system had the building loop directly piped with the geo field system in a primary/secondary configuration. The new piping arrangement has a heat exchanger between the geo field and the building loop... Wonder if that heat exchanger is under sized for peak load.
    PHM
    --------
    The conventional view serves to protect us from the painful job of Thinking

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    I had a customer w/geothermal connected to 150t of chillers. The ground/earth "overheated" during our winter so they installed an air cooled fluid heat exchanger until a cold snap froze the heat exchanger and ruptured lots of passages. At our 1st meey=ting I asked a few pertinent Q's and all of a sudden the meeting came to an abrupt ending. It seem that I put some peoples expertise in jeopardy as "they" had self engineered the system design and screwed things up. The customer spent $400k doing "in-house" renovations w/o any good results. The Co-curator told me that I have a nasty habit of asking "the wrong Q's" ,I smiled and said "Why thank you,Sir,I appreciate the compliment" as his neck and face and bald head turned an odd shade of red.LOLALOT.

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    Quote Originally Posted by TechmanTerry View Post
    I had a customer w/geothermal connected to 150t of chillers. The ground/earth "overheated" during our winter so they installed an air cooled fluid heat exchanger until a cold snap froze the heat exchanger and ruptured lots of passages. At our 1st meey=ting I asked a few pertinent Q's and all of a sudden the meeting came to an abrupt ending. It seem that I put some peoples expertise in jeopardy as "they" had self engineered the system design and screwed things up. The customer spent $400k doing "in-house" renovations w/o any good results. The Co-curator told me that I have a nasty habit of asking "the wrong Q's" ,I smiled and said "Why thank you,Sir,I appreciate the compliment" as his neck and face and bald head turned an odd shade of red.LOLALOT.
    Yup... As the controls guys we are there to drop those questions quite often, since it seems that we're the ones who have to plan out how all the different parts are actually going to work together.

    I have a lot of customers who really appreciate us asking those questions if we can, before it gets too late.

    Sent from my SM-G950W using Tapatalk

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    Did the loops get flushed properly. Some of it could be air-locked and not circulating through part of it.

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    Plate HX could be an issue if that is what has changed over 25 years of operation.

    You can make an iceberg underground! I also feel that seasonal "recharge" could be a factor along with the HX and new properly functioning equipment.

    Is this horizontal loops, slinkeys or drilled wells?
    A dying culture invariably exhibits personal rudeness. Bad manners. Lack of consideration for others in minor matters. A loss of politeness, of gentle manners, is more significant than is a riot.
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  19. #17
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    Lets assume and "expect" the system including the loop was installed properly ~25 years ago.
    25 years is an expected time frame for the equipment to fail and be replaced. We replaced a 5 x 10-ton municipal system last year after 30 years of use.
    With the loop temperature dropping that fast I suggest you start with #1 the circ pumps are designed for the flow rates, #2 the loop is flushed and burped properly.
    I do not agree the consultants comments!.....but then again experienced geo consultants are a rare find
    Attitude is the difference between and ordeal or adventure

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