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geothermal vs. airsource

probably restarting an obvious thread here although i ran back through the last couple months and didn't see anything that jumped out.  i apologize if my search wasn't exhaustive enough.

The thing that chased me over to the heat pump forum was actually the EIA price/btu comparison chart posted on a propane vs. oil thread (where i normally troll - well hopefully not)

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I'm glad i clicked on it, although i don't need the help for conventional fuels, I noticed the efficiencies for heat pumps.  now i had never thought of it this way, but of course they would enter in a table like this with efficiencies greater than 100% because they deliver more btu's per kwh than direct 100% conversion of kwh to btus through resistance heating.

so to develop a comparison model you look at how many more btu's and that becomes an efficiency greate than 100%.

and i was long aware that ground source heat exchange could keep heat pumps producing when outdoor temps dropped below operating parameters for airsource.

The thing I hadn't wrapped my mind around was whether ground source was actually more efficient than airsource. you figure you got a fan moving air or a pump moving water. maybe i can see moving the amount of air involved as more power consumptive and the heat exchanger as larger so there is a little bit more load on the refrigeration compressor from the head loss across the heat exchanger. But i hadn't considered that to be such a significant source of savings.

well, according to the EIA worksheet, an 8.3 HSPF airsource is 240% efficient while a 3.3. COP groundsource is 330%.  If i read the fine print these differences are not related to temperature zone and percentage of time running on backup assumed not to affect groundsource.  They have a separate chart below that calculates operating efficiency in certain geographies from the HSPF although i guess there must be some allowance for an avg. ambient in the HSPF because in a very few, very warm locations, e.g. Miami, the corrected HSPF is actually higher than the nameplate HSPF.

So as best I can tell, the 90% difference between groundsource and airsource is related to the efficiencies of heat transfer. I wouldn't have guessed it was that high.

you learn something new everyday.

so I missed my opportunity to caress a bunch of these babies at AHRExpo because I was so busy chasing down hydronic control and pumping strategies and i have to start from scratch.

While the minisplit airsource is a fairly robust approach, one other thing that attracts me about a groundsource approach water to water is that it will retrofit into most any radiant hydronic application and it isn't a split unit.  rather you get groundwater feed and return in one side and system feed and return in the other.  so that seems to me like it should be a cheaper unit to design and manufacture than a mini-split with the exception that you just aren't going to see as many units esp. early in market adoption but there are always going to be less situations you can use water to water.

And where do i go for entry level primer like converting tons to btus for comparison to boiler capacities. how one calibrates for higher desired water temp. in that equation and what are the highest water temps  available. what do horizontal field sizes look like in terms of pipe length and dsq. or cubic area of ground most appropriate to those pipe lengths. and what manfuacturers and distributors are big in these so I can look for actual unit costs. Because getting stoked on all the energy savings can be dashed by the infrastructure investment.

After all wind and solar are free, so we would all have them but for the cost of the infrastructure (and those fussy reliability problems so add storage or grid back-up to those infrastructure costs).

And one thing occurs to me which is not specified in the EIA worksheet.  I'm going to assume that their 'typical' efficiencies might be calculated with condensor temps around 140. am i right about that and how much do higher or lower design water temps affect the efficiency?

Pointers appreciated so i can learn enough to ask some real questions.




  • Jack
    Jack Member Posts: 1,045
    Geothermal is great...but

    It is very pricey. The day the enormous tax credits go away is the day that business evaporates over night. Basically, they are selling tax credits. That was what happened to the solar business. Better to look at mini splits which are tickling the COP/HSPF's of the geo for a fraction of the cost. Also, I think the max output on the geo water to water is not above 140. Correct? Back in the 70's I was doing geo with a glazed solar system heating a pool and driving the hp with pool water. Had to be careful on the cooling side though. Also, I think you have to look at pumping costs as well.
  • SWEI
    SWEI Member Posts: 7,356

    on modern VRF ASHPs are competitive with those on older GSHPs. The latest batch of GSHPs with VRF have raised the bar even higher.  I would suggest a consultant,  engineer, or contractor who is up on the latest offerings as the field is changing.
  • icesailor
    icesailor Member Posts: 7,265
    Groundwater Source?

    I'm not trying to give opinions either way. But if the Geosource is groundwater, there are some things that probably aren't in the equation. Wells aren't cheap. And you probably need two of them. One as a return injection well. Even more important is the quality of the groundwater. All the X GPM's of 55 degree water mean squat if the quality of the groundwater has the ability to totally insulate the HX in 6 months. Or, the ability to seriously restrict the injection well screen. What do you do with the overflowing water on the return well? Where I used to work, there was always someone that thought that "common Sense" was a monetary value and put in one of these systems going back to the 1970's. I never saw one work more than two years because of water quality issues. There's something to be said about the quality of air. Its always around and as long as we keep breathing it, it should work on a heat pump compressor.

    Then, there's that chart with the electric costs.

    They always give you costs in some listed by the power company's as something like ".015 per KWH" or some really low number. Having seen the hydronic heating market eliminated where I used to live by the power companies advertising these teaser rates to get everyone to switch to electric resistance heating, I didn't buy it. I saw customers leave for electric heat because of this "$.015 per KWH rate, but that didn't come until you used over 2000 KWH's per month. I would say, take the whole sum total of your monthly bill and divide it by how many KWH's for your true monthly cost per KWH.

    They never did, but then again, a lot of them were stuck with their decisions.

    No one ever tells you what their actual true monthly costs are. Its a secret. Sort of like how often you have personal relations with a significant other. Its just not discussed. Bragged or lied about. Little or no truth.
  • archibald tuttle
    archibald tuttle Member Posts: 810
    too good [read expensive] to be true

    so i'm guessing there is a second wave early adopter problem on the expense

    side for water to water.  I can't think that the heat exchangers are much more expensive and

    there is no split, but maybe the units ain't so mini if they are aimed

    at boiler replacement (only one i've even found is Bosch 10 Ton (still can't find reliable converter of tons to btus)

     sounds like this unit is actually a twin 5 ton if i read the literature right, although i can't believe they wouldn't be using variable speed compressors to adjust for load rather than staging - that seems so 90s.

    i am as skeptical as the next guy, maybe more so, when someone says something is green but costs a ridiculous lot of money.  costing a ridculous lot of money is the opposite of green in my book, because if it is really green it won't be widely adopted and if it is just a tax rebate scam I detest it for that reason.

    all that said, radiant heat can risk being ridiculously expensive when you look at some of the emitter systems but i was doing this on a shoestring out of mother earth news 30 years ago when nobobdy was interested in paying for 'radiant' heat.

    i wouldn't be planning to pump groundwater and reinject.  i'm looking at ground and/or pond loops.

    i've got an excavator and lots of space and it clears my mind to dig holes so not too much opportunity cost on that side.

    I've got ponds and unlimted flowing water but they are a little far from the buildings.

    i'm still contemplating.  thanks for the input.  i gotta friggin go to work.  details at 11.

  • RJ_4
    RJ_4 Member Posts: 484
    heat pumps

    Two interesting installs        (1) A high end residential ground source heat pump job,  In northern Ca with piping set in wells hundreds of feet deep, everthing looked to be installed and grouted correctly,  the problem   when the soil around the wells was moist the system worked ok, when the soil was dry the units would trip on high head the cooling mode.

    (2) A large software co in Silicon valley ca   large heat pumps using a pond for the heat source, worked ok until the geese moved in, some of the goose poop ended up around the coils in the pond effecting the heat transfer.
  • Jack
    Jack Member Posts: 1,045

    I worked on the Geysers geothermal power plants ,in Healdsburg, CA back in '77. A bunch of dry steam wells would be piped to a small power house. It was great because rather than on a nuke where you could work on 1" ss piping for a year and never find out what was going to go through it, on the geo plants a couple dozen fitter and welders would build a plant that you could see coming out of the ground. Check out the Geo Heat Center at Oregon Institute of Technology in Klamath Falls for some high temp geo info.

    On residential systems we used to also use a ditch witch to trench and install poly solar collectors on edge and bury them with sand. Drip irrigation on top to keep up the heat transfer. I think it was Sola-roll we used. Of course that was in the Napa Valley and you didn't have to worry about freezing ground.

    The other thing about geothermal systems is you had better have an A1 guy do it. Wells and piping, ductwork, HP and controls. Not for the faint of heart,imho!
  • archibald tuttle
    archibald tuttle Member Posts: 810
    thanks for the war stories

    so one real world complication i imagine i need to think about is good heat transfer between the coil in the ground and the ground itself.  I'm thinking 1" black poly maybe 4 500 foot coils manifolded reverse returned though 2" to the heat pump.

    the biggest complication i've seen reported is poor heat transfer in those coils.  some folks talk about constantly saturating the ground to get transfer.   i'd probably rather avoid that approach in favor of careful use of dense fill - i don't know sand, stone dust some clay? surrounding the actual pipe.

    my best estimates dealing with a few guys who have put in some of the early systems around here is they calc 25,000 btus per 500 ft. coil. and i'm targeting a 100,000 btu appliance so seems ok.

    also my best estimate is that 1 ton is about the equivalent of 25,000 btus. 

    i don't know but i'm thinking my cheapest alternative may be something intended as a water heater rather than a boiler to get going or i'm going to have to piece my own together.

    i'm kind of into giving this a shot but i've got a year to mess around, bury pipe. think it through, etc.  i've got almost infinite space and an excavator so i can overdo the ground exchanger coils.

    so i'm down to individual battle level questions that will come from time to time as i pursue this.  open to any recommendations for good price point water to water units including hot water heaters vs. 'boilers'.


  • Harvey Ramer
    Harvey Ramer Member Posts: 2,217
    Ton of Refrigeration

    1 Ton = 12,000 BTUs

    Geofinity (Modine) has a hybrid geo unit. Water to water and water to air. Good combination, don't you think. Radiant in the winter and AC in the summer.

    The bigger you make your loop field the better off you will be. I would try to do intelligent pumping as well.

    At this point with conventional heat/cool geo units 115°F water is the max you should design for. 120° is the absolute max and should only be used if you are running ODR.

    There are some heat only geo units that will do 140°

    Those are the parameters last I checked.


  • RJ_4
    RJ_4 Member Posts: 484

    Water furnace   makes a good product and I believe they have engineering available
  • Techman
    Techman Member Posts: 2,144
    geo vs air

    Across the board, what is the lowest evap temps heat/cool that the refrigeration system/compressor will be subjected to?
  • Eastman
    Eastman Member Posts: 927
    a lot

    And one thing occurs to me which is not specified in the EIA worksheet. I'm going to assume that their 'typical' efficiencies might be calculated with condensor temps around 140. am i right about that and how much do higher or lower design water temps affect the efficiency?

    don't assume, pick a major company like waterfurnace and check the online docs. you will find tables that indicate cop is highly dependent.
  • TonyS
    TonyS Member Posts: 849
    water to water

    I heat my home with a water to water heat pump. I had a well that was clocked at over 32 gpm and 5 ft from the surface.I also have a stream aside of the house for discharge. Water temps remain constant at 55. Hydronic separation with a 40 gallon buffer tank controlled with a tekmar reset control usually running 100 degree water through radiant heating system. COP depends on water temp discharge which changes with outdoor temp. Water from well #5 ph so cupronickel exchanger was used and seems to be holding up well.

    The downside is noise, unit is 36000 btu and compressor is in attached mechanical room. Very annoying. Compressors dont seem to get quieter with age.

    It works well and is very cheap to operate. Invested in a inverter constant pressure pump to maintain correct flow rate but will replace with smaller pump and cycle stop valve to get same results with lower pumping cost.

    I have seen some of the systems that use closed loops and wells and have heard the prices people pay for them. To me it doesnt make any sense. Air to water heat pumps will give the same comfort and the money saved will put an entire array of photovoltaics to run it. Efficiency becomes moot at that point because the air to water system would run for free. Photovoltaics have been dropping in price and I really like the plug and play convenience of micro inverters.
  • TonyS
    TonyS Member Posts: 849
  • archibald tuttle
    archibald tuttle Member Posts: 810
    lowest evap temp

    right, so i haven't ground truthed thes modeled numbers yet but according to this nice chart from virginia tech that has nationwide mean well tempature contours, we're about 50 degrees. with a swing at 6 ft.depth of 10 deg. +- and 7 deg. +- at 8 ft. depth.  That actually depends a little on soil type and their chart shows my soil types (dry sand) having swings as low as 5 deg and 3 deg. at those depths but the text suggests dry soils with higher air content have less storage capacity and are subject to higher swings in temp so i went with the more accentuated curves for now.

    So that suggests conservative low evap temp of 40. that doesn't seem as rosy as most of the geothermal equipment manufacturers represenations, e.g. water furnace says that the temperature 3 feet below the frost line is between 55 and 70.  I assume they sell a lot of units in Georgia.  I'm particularly unimpressed with their documentation on this temperature question.  Installation simply specifies 15GPM standard, 20 GPM if temp is below 50 deg.  and 25 GPM for some other unspecified issues with load and ground resource.

    there is no table and no discussion of how this affects efficiency or how hydronic supply temps affect efficiency. although maybe i could go to a pump manufacturer and try to calculate what the pumping load would be as between 15 , 20 and 25 GPM on the required length of loops.

    The tech at this point all seems focused on staging, not variable speed compressors. I don't know if you would get modestly different running load amps if evap temps are at the lower end of operating range rather than higher, or simply get the same amps with lower water output temps.  Probably has a variable meterting valve before the evaporator designed to keep the same apparent load on the compressor but that is just a guess.

    So assuming you got the flow rate, maybe low ground loop temps keep the second stage running more.  that is an obvious extra electricity load.  but there just is no literature on any of this i can find on their website.  maybe i should be checking another manufacturer.


    PS  - i notice folks talk about pond sourcing. i've got ponds out the ying but the water temps there aren't gonna be any 40 degrees. Again, I think they are focused on Georgia, might be a growth market given this winter, but I'm disappointed in the documentation - not only because i have to retch at all the climate change crap and subsidy talk but because there is not much of substance there to help anyone really look under the hood.  the savings calculator is a useless black box.
  • archibald tuttle
    archibald tuttle Member Posts: 810
    water furnace docs not worth paper not printed on


    i notice a link below to another manufacturer i'm going to go check but i could find nothing useful on water furnace site.

    i also notice he's got a great result but he's using open loop surface discharge with 55 deg. water.

  • archibald tuttle
    archibald tuttle Member Posts: 810
    thanks for first hand heads up


    you must live in a slightly more friendly zone.  our well water is 49-50.  so that isn't right out but not quite as good as what you've got.  i do have streams although the discharge piping would be on the order of 500 feet.  i guess if i put in 2" and that is going down hill that doesn't create an insurmountable load.

    although i do have an old 20' dug well that is much closer that i could try and i bet that could take 20 gallons a minute. although i've got several buildings to do eventually and if i start bumping that to 40 or 60 gallons a minute don't know.  Don't know if i could get a well with those yields either.  I've got that kind of supply with ponds no problem but then we're talking longer lines and lower temps.

    i have fairly infinite space and my installation tools so ground coils aren't out of the question compared to what folks might have to pay if they don't have acreage and an excavator. But I still think low 40s is the best i'm likely to deliver by late winter from horizontal install.

    Aside from ph are you running the ground water right through or is the cupro-nickel exchanger to keep the open loop water out of the heat pump itself?.

  • TonyS
    TonyS Member Posts: 849

    The actual amount of water going through the Geo is 4-1/2 gpm. With fresh water you only need 1-1/2 gpm per ton. Close loops are double that. I was just saying that my well could easily feed the geo unit and all the house usage. No need to dig another well.

    Cupronickel is offered by all manufacturers as an option, cheap insurance as well water can change over time.

    I also filter the water with one of those centrifugal sediment removers, they work well and are very easy to blow out even when the units running.

    The pipe going to my stream is only a couple of inches underground but pitches continuously toward the stream so it drains down when finished. Never had any trouble even with sub 0 weather.

    I dont cool with mine...chilled water is a pain to insulate and pipe. Ductless mini inverters are to good to waste your time and money on chilled water. So you wont need a desuperheater option, they only work in ac mode. If you want to make domestic hot water you can pipe it like a boiler with an indirect water tank.
  • TonyS
    TonyS Member Posts: 849
    One other thing

    There is no magic to them, the press likes to talk them up but they are just a heat pump with a water cooled condenser and in your case it just thinks its 50 degrees out all year round. Just a plain old Copland compressor and a couple of heat exchangers.
  • icesailor
    icesailor Member Posts: 7,265
    Well Yeld:

    I have to ask:

    A well and pump at:

    20 GPM is1200 GPH or 28,800 Gals. per 24 hour day.

    40 GPM is 2400 GPH or 57,600 Gals. per 24 hour day

    60 GPM is 3600 GPH or 86,400 Gal.s per 24 hour day.

    Do you have wells that can sustain these kinds of numbers and a place to get rid of it?

    If you have ponds, do they have something that will allow those sustained yields?

    Are they "Perched Water Ponds" (above the aquifer) or "Groundwater Ponds" where the pond water is the level of the ground water?

    I was called in to a large commercial public building that was designed as a truly green building. It won awards for being such a green building. The architects ripped out the entire fossil fuel heating system. With no back up. Cold groundwater was never an issue. It was UNLIMITED. They installed 4- 160 GPM pumps in 4-10" wells. The mechanical room was most of a cellar area. I believe it was a Water Furnace design and equipment. It didn't work for heating or cooling. Everything in the entire system was based around this underpowered system. The manufacturer of the equipment walked away or became difficult to converse with. The installing contractor was paid and wanted nothing else to do with it. The mechanical designers were no where to be found, and some guy in Rhode Island in an office, controlled the whole operation with his lap top. I never saw more than a 10 degree Delta T at the HX's. I told the powers to be that the HX's needed to be cleaned. ANNUALLY and they hadn't been cleaned since installation. Speaking to the driller, the screens were set in glacial shells and had high TDS levels. I wasn't doing any part of any of the repairs. I was there doing some plumbing. The problems with the buildings were so bad that they had a change of administration. Smarter people than I were brought in because they had cheaper ideas. One being that as far as I know, the HX's still haven't been cleaned. But the pumps still pump at 160 GPM. Its cold in the Winter when it is cold, and employees use electric heaters to stay warm. And hot in the Summer when it is hot and the employees use fans to blow air at them. .

    I'm sure that there are GWHP's somewhere that work well. How well is the question. I'd like to meet one that has been running and saving $$$ for as long as the basic, average fossil fuel heating system.

    You never know what's going to screw the pooch (as some of us sailors say). Who ever knew that Goose Poop would screw up a pond system.

  • Eastman
    Eastman Member Posts: 927
    edited February 2014
    here is an example

    click on the specification pdf

    go to the section on performance data

    might need to decipher a few acronyms

    it seems like that table is for full capacity, though. i wish there was one at partial load. i also wonder how hard these sytems would be to integrate with wood.
  • archibald tuttle
    archibald tuttle Member Posts: 810
    thanks for the pointer

    i looked at that unit but so much for thoroughness.  the Specificiation link is the only one i didn't click on because the singular usually means lingo for architects to spec that particular product,e.g.: will be a dual circuit heat pump with dual hydronic high nickle heat exchangers and really neato controls, etc., etc., etc. --  so i looked at the brochure and at the installation manual thinking that that kind of info would be in one of those.

    chagrined, as i am, went off to read the stuff. So generally what i expected.  The only thing about the performance table at the end of the packet is it isn't clear whether there is any carryforward of the pumping correction added to ASHRI/ISO calculation at the beginning of the packet.

    the ISO calcs associate EST (entering source temperature) with different technologies. For Ground Loop they use 32 deg.  That is maybe a hard case but quite more realistic that the 55 to 70 deg. touted in the Water Furnace brochure  (maybe when I saw that I thought they weren't serious and that is my excuse for skipping the link i needed).

    Once you have a technology associated you can assume a source pumping rate and they include a calculation so I believe that the ISO COP includes the water pumping electricity, but apparently only the pumping loss of the heat exchanger itself.  And, to complicate matters, they use round numbers in their performance table instead of matching the typical scenarios from the ISO test. So I can't precisely compare the ISO calc and the performance table to see if the performance tables include pumping load or not.

     (It is explicit that they factor 15% antifreeze of leaving water temps are below 40 deg. That seems a little on the cautious side if they've got a good flow switch and controls although I guess it can help with nuisance lock outs. I have found it is safe to run water down to 35 in chiller towers as long as you have good flow monitoring but they do have much more open passage heat exchangers. Antifreeze is such an ambiguous thing.  Finding one that doesn't have a corrosion and btu penalty is like finding a decent battery for storing intermittent energy - i.e. might make it practical. But i digress . . .)

    The reference calc for the performance table appears to leave the pumping correction out. But there is a reference table of pressure drops, presumably just across the heat exchanger. But the reference equation for the pumping correction in the ISO calc is ambiguous itself. It appears to only contemplate the pressure drop of the heat exchanger itself, but there is going to be head/lift if you are pumping out of a well (somewhat offset if you are reinjecting) and the piping loss for well, surface water source or for the ground loop.  So one is still in the dark as to whether this is really an adequate comparison.

    I could use some help here because I'm rusty on parallel piping technique to calc. the drop for a multiloop reverse returned ground setup.  assuming 500 ft. maybe even 1.25 to reduce head loss, you get about 29 PSI for a single 500 ft. run (although I'm not sure if you need to adjust that for loose coil burial or whether bends over a certain radius look 'straight' to the pump.

    If I read explanations correctly, parallel piping doesn't reduce that head loss but increases the flow for a given head loss so what i should do is divide my flow rate by the number of loops.  then i get a more manageable 2.95 psi drop for 4 loops.

    and maybe another 1.5 psi for 250 ft. of 2" main.

    if I call it 5 psi to be conservative their pumping calc would add 181.3 watts of load or about 3% more than the calcs in the performance tables for 30 deg. EST and 100 deg. ELT which is pretty close to the ISO scenario and shows an equivalent COP of 3.1. So that would drop the COP to 3.05 or conservative rounding to 3.0.

    So as i work it out not too much of a factor.  Obviously the ground loop temp is a much bigger factor. The COP if the EST were 50 deg. would be 4.0 or a .9 increase. Increases in 20 deg. increments about that art .7 which suggests that the antifreeze penalty for 15% is about .2 on the COP as that is the only difference between 30 and 50 vs. 50 to 70 and 70 to 90. That is commensurate with their antifreeze tables but, their tables give figures for 10% antifreeze and 20% antifreeze but not for the 15% they choose as typical.  Again, there is a disconnect between their tables over the course of the literature.

      Would be helpful if they were a little more explicit about the calculations so you could convert them to actual water temp but seems like extrapolation at .35 per 10 degrees would give me a COP of 3.45 of 3.4 allowing for pumping at 40 deg. water temp and running 15% antifreeze.

    So the biggest crap shoot from all the horror stories like ice sailors green building is water quality and protecting the heat exchangers.  I have high ph, not quite coca cola grade but getting there - its. rock water.  But not a lot of dissolved minerals. Closed loop has better ability to treat and have stable water quality. So I need to learn better what are the best ph buffers and which would be the best antifreeze to choose with these heat exchangers?

    MEanwhile, I'm going to put a temperature gauge on my incoming domestic water and monitor for a while.  It is 5 foot underground runs 200 feet in 1.5" poly from another building which is connected to the well by another 100 feet of pipe, so the first morning flush should give me a pretty good conservative estimate of ground temp to work with.

    Any other help with whether my estimate of pumping as a single digit effect on the COP is correct. Heat Exchanger maintenance (and assuming that the key threat to the exchanger is from the exchange fluid side and not the refrigerant side?) 

    another sunday novel

  • Techman
    Techman Member Posts: 2,144
    edited February 2014
    evap temps

    With an evap temp of 40*f would that give a Freon temp of 20* ,inside the evap ?Like AC.
  • archibald tuttle
    archibald tuttle Member Posts: 810
    modest misunderstanding

    got it on the lower pumping assumptions for ground water, although you've got fairly low tons in service.  the water furnace hyrdronic to hydronic is looking for 15 gpm on well water, obviously at full operation -- it is two stage.

    But their figures are still a little more conservative, because that would be 2 gpm per ton, but close enough for government work or seat of the pants  - which all of this is until it is more affordable. i don't care how much rationalizing you can do about the theoretical savings, sticker shock is still sticker shock. 

    what the hell do these things cost. I'm not looking for super proprietary or snide competitive sniping between wholesalers and manufacturers kind of pricing that would get dan all worked up in a lather.  i'm talking ball park.

     i notice that everybody pushing them offers savings calculators, but no prices. kind of says to me, if you have to ask you can't afford it.  and they do give the rebate numbers at $2100. if that is 30% which i've heard quoted then we're talking 6 or 7 grand?

    got to see one of these centrifugals although i'm pretty sure i'm talking closed loop.

    how long has yours been in service? any noticeable degredation of heat exchange.  you'd need pretty good logging to really track that i would think. i would hope for you 6 or 7 grand you could just plug into a usb port and take a month's readings for every 5 minutes or something.

    i'm ambivalent about cooling.  we use whole house fan approach and it works great. only a few days a year i wouldn't mind the dehumidfication i could get from the cooling side.  if i used it cooling wise, it would just go into an hydro air handler for a couple key spaces with the condensation handled principally at the water to air exchanger, and limited feed ducting with insulation in unfinished space.  of course that system could double as heating supplement in the winter because that core area of the old house is the only part that isn't radiant floor at the moment, but that still would require the higher temps. might look at retrofitting a couple floors in hear and getting off high temps all together.

    that said, the water furnace is distinctly a reversible heating and cooling appliance, albeit there is the desuperheater option. but i seem to recall that earlier discussion on the thread suggested that an appliance that was not compromised by reversibility could be an even more efficient heating appliance.  I don't seem to see this in the water furnace line.  anywhere else?
  • archibald tuttle
    archibald tuttle Member Posts: 810
    with 20 deg. freon temp you get . . .


    water furnace seems to recommend antifreeze if the LST (leaving sourcewater temp) is under 40.  If it is 40 going in, of course it is going to be under 40 so i'm beginning to factor that into my planning, although i have to do some[sorry]  groundtruthing. This would be the coldest time of year for the ground coming up so i'm going to install gauge on my cold water infeed that has long ground run in plastic from another building.

    anything else to worry about with 20 deg. freon?
  • TonyS
    TonyS Member Posts: 849
    Here is a performance chart

    on the unit I have.
  • archibald tuttle
    archibald tuttle Member Posts: 810
    geez they rate em in Kw

    can't friggin win.

    i assuming you have 036 maybe .  extrapolating from the BTU capacity I think the 120 is a little bigger than the Water Furnace model i was looking at and has modestly better COPs (10%) at given conditions.

    They do have a 40 deg. table in their charts, nice.

    still haven't seen a heating only model . . . are they really better on the COP end?

    are the compressors slightly more efficient, more likely to eventually get variable speed compressor technology just like the fluid pumps we have now?

    as far as hot water, i hear EPA is going to be making some big push for heat pump hot water heaters. typical of them to push something that is expensive and not parrticularly workable. you're talking a delta T of load of maybe 70 degrees.  of course the ELT is much lower but the desired LLT is up there at the high end of design.

    someone, can't remember who, and when you reply to one message you can't see the rest - how bout fixing that dan -- suggested an indirect. i don't get how that is gong to work wiht any kind of recovery. all the controls i know bump system output to max, maybe 180 or 190 degrees to make hot water.

    i guess if you can put up with buying a really expensive water heater and waiting 4 or 5 hours for recovery, its perfect.  that does kind of describe solar but there is a reason so few people have adopted that and its been around longer than any of these technologies.

    not to mention that on demand gas water heaters are getting to be reasonably bomb proof.

    thanks for the charts from another manufacturer though. gives me something to go on and competing manufacturers to price. my local whosesaler has bosch so now i'm up to three.  how much do these friggin things cost - give or take? i assume it is kind of an entry level thing so you don't pay a lot less per ton on larger units although without variable compressors you may sacrificew a bit of efficiency at low loads.  But I've got enormous place and multiple buildings so i'm more likely to buy a big unit if the price per ton is better.  at some point i'm sure they stop making them bigger and you stage the units (beisdes internal staging).

  • Techman
    Techman Member Posts: 2,144
    edited February 2014

    With a 40* evap and 20* or so Freon temp then the following holds true ,I think. AC is 12,000btu/ton/evap/per horsepower, 5t=60k btu=5 HP comp motor.there is 15,000btus of heat rejection . Assumeing a 20* Freon temp then that changes the btu/ton/hp ratio. At 20* Freon temp, that  turns into refrigeration , at 20*the btu per hp is about 9,000btu. 12,000btu is still one ton. This is from the comp mfrg , chart of suction press/evap temp range,vs btu, thing.
  • Eastman
    Eastman Member Posts: 927

    what type of system are you trying to heat --what temperature do you need at design conditions.

    you can see from the charts that the cop drops off if one needs high system temps. i was surprised though, that the btu output doesnt drop too much. and i wonder how that compares to airsource.
  • archibald tuttle
    archibald tuttle Member Posts: 810
    edited February 2014
    system temps mixed


    I get that the lower the temp you can take your btus the better the COP. As you noted the btu capacity is not so much affected by the high load temp.  Rather it is the running amps. 

    I'm trying to visulaize the push pull in heating mode.  So the compressor has to

    create enough head to condense at a given temperature.  so I think the thermostatic expansion valve would throttle in such a case and you get higher head pressures, thus more compressor load. This is the source of the decreased COP. It isn't that you get significantly less BTU's, rather you use more electricity per btu.

    This is the compliment of the effect of low source temp which lowers the BTU potential significantly with only a modest increase in electric consumption. The key factor is the difference between the source and load, the less difference the better, but it manifests in slightly different ways.

    my loads are part floor radiant that i run on the warm side in glass rooms.  120 is plenty. when i'm feeling parsimonious i drop the design to 110 -  working on automating multiple honeycomb shades to cut his temp; and part baseboard with a fair amount of element and aggressive reset that stays at 148 supply down to 20 outdoor temp. (highest tabled LLT for the water furnace, the Genesis doesn't chart above 130.  Don't know if they rated up on btu's and would move outside the parameter if they charted higher or what is actually that different between these manufacturers. I still have yet to see a heating only unit and whether it can peform any better by being optimized for unidirectional operation. that has been touted for heating applications but haven't found any)

    with more radiant coming on line I'd say the load will be split about 3/4 radiant, 1/4 baseboard.  So i'd be supplementing for some of the load with propane in coldest weather until i finish figuring out radiation for the original kernel of the house that has baseboard.

    i'm using an indirect for hot water now, so i guess i can heat pump into that when i'm not fulfilling heat demand but at a temp of 148 it isn't exactly going to be quick recovery or at the better end of the COPs - but even at 2 it is still a modest hedge against propane.  would do alright for overnight and daytime recovery. probably have to

    supplement a couple days a week. Thats going to take some control

    strategy, and, knowing my luck, nobody has made the control that will do

    what i need.

    At my summer propane prices, a COP of 2 would only be a 15% savings. average cost since i buy up to half of my propane during the season could hedge 30% there although I'm sure more storage would be a cheaper hedge, esp. because electricity will inflate just as fast as propane (absent the spikes), not least of which, because of all the stupid alternative energy mandates and

    rebates for heat pumps coming out of my electric bill, my electricity

    prices are going to pace propane so i suspect that advantage will be

    fairly constant over time. (i'm ambivalent about whether i should take a

    rebate from a program i disagree with so i have more money and resouces

    to fight programs like that, but i digress . . . ).

    I've gotten a little interested in this technology in the same way i was interested in radiant floors 35 years ago. If I can do it on the cheap and help in any small way to improve the availability of a good technology in other than high end applications I might be inspired to invest more opportunity cost and maybe even a few more dollars to get something like this going albeit i got a hundred acres, so a couple more thousand gallon propane tanks will fit pretty easily.  Additionally I am looking for ways to move my radiation loads towards 110 degree temps, not only in the experiment house of glass where i live, but in several other residential and work buildings. And i need to spend some time plotting out how much time i spend in the range of design temps vs. the real world.  With envelope, radiation and outdoor heating season medians vs. design  I can probably get an average COP towards 3 which starts to look a lot better.

    still trying to figure out what one of these units costs. that is still a highly guarded military secret.  i'll find out about the Bosch at local wholesaler this week.  Also still searching for the mythical heat only unit optimized for heating service if such a thing exists. and trying to check my calculations on source pumping wattage.

  • NYplumber
    NYplumber Member Posts: 503
    Air to Water

    Good conversation going here. Curious to read the outcome if you ever go through with the install.

    Have you looked into the Daikin Altherma? Less pumping loss, no need for glycol, no worry that the ground will dry up, etc. There may be competitors to the Altherma, however I have not looked into it.
  • archibald tuttle
    archibald tuttle Member Posts: 810
    edited March 2014
    NY Plumber et al

    we're probably in about the same ground and air temperature zones. 

    the Dalkin Altherma website is pretty lowlevel marketing to end consumers.  no good info i could find on how these units compare to the ones i've been looking at.

    I did just find the multi-stack company out of wisconsin and talked to the only engineer i have yet to find at any of these companies who offered comparative knowledge of refrigerant suitability.

    I have been asking for any info on units optimized for heat.  As best I can tell, the physical units multistack has are about the same but are designed to run and have specs for both 410a and 134a.  (I will be getting back to them to see if 404a or 407a are possible considerations as well as I'm told there is a considerable price advantage, at least for the 404a over the 134a, and that performance characteristics are somewhat similar but it has higher Global Warming Potential (which i don't worry about much, i'd prefer to know how it does as a refrigerant, this is, after all refrigeration we're trying to do here. typical of focus on the wrong thing, it is ten times easiers to find comparisons of the Ozone Destroying Potential and the Global Warming Potential of these materials rather than their refrigeration potential - esp. with regards to heating.  There is a fair amount of discussion with regard to cooling as R-12 replacement in cold temp food storage applications. It's fine to note the ODP and GWP given the regulatory focus, but the friggin' regulators seem to be forgetting one thing, refrigeration=civilization. So you aren't just cutting your nose off to spite your face when you make a mistake in regulatory judgment here, you are cutting off arms, legs, reproductive appendages, etc. Thus an overly precautionary level of regulation is actually antithetical to precaution  - but I digress . . . ). There is also a 404a alternative 407a.  Again it is very hard to find useful cost comparisons, refrigeration operating characteristics with respect to geothermal heat pumping, inluding information on the date of expiration of any patent which may be an indicator of future cost (absent the reality that there may eventually be regulatory risk on high GWP refrigerants).

    The important distinction between R410a -- used in most heat pumps that are really repurposed air conditioners -- and R134a is the acheivable spread in geothermal application between leaving source water and leaving load water.  for 410a it is 105 deg.  for 134a it is 135 deg. (hey dan, since we're all so concerned with efficiency here, it would be nice if there were some button that would allow us to insert the degree symbol). The efficiencies are fairly similar and the head pressures for R134a are actually med. rather than high as experience with 410a.

    That makes it intuitively obvious that 134a is far superior for heating provision from heat pump systems.  The downside for reversible systems is that the cooling capacity (not efficiency) is about 40% lower.  That doesn't seem like much problem for our climates in the NE as the spread between indoor and outdoor design temps is smaller for cooling than it is for heating meaning that the cooling load for any given space will be less than the heating load by perhaps a similar or larger percentage.  Insofar as I can see, the idea that anyone would sell a geothermal heat pump north of the mason dixon line with 410a is part of what is setting the industry back and earning a buzz equal to early low flow toilets.

    More than half of the early adopters I've surveyed have abandoned their geothermal systems or sold the houses disgusted with the performance. Yet when you inquire into what went wrong you almost always find that the pump was incapable of heating because the source and load temps were not properly matched, although they might have been if a different refrigerant had been used.

    I'm a 'heating help' kind of expert at this point.  I'm operating on research, intuition and anecdote. So I don't mean to say that the sample I've taken is scientific or truly representative of this industry  It is just the impression I have gotten.

    But the more I look at it, the more I see that refrigerant choice is potentially critical. Open to correction here.  And would like to understand what the actual present costs vs. future costs of these refrigerants is, weighing patent lengths, actual manufacturings costs, markets, etc. Anyone who has sophisticated knowledge in this area or pointers to same, much appreciated.

  • Techman
    Techman Member Posts: 2,144
    Refrig temp/press

    Just a thought.This is on the Freon temps/press for different freons.  On a 95* ambient the head press/temp is no higher than 120-125*f condensing for each of those freons you mentioned . That 135*f for r-134 is a little high.
  • archibald tuttle
    archibald tuttle Member Posts: 810
    not sure of the math to derive that . . .

    an engineer at multistack gave me those spreads.  do you think the R410 spread is on at 105 but the R134 is more aggressive at 135?

    looking at their literature,

    they table their 410A units up to a 63 degree spread and never show out of range conditions in the tables.  they go up to 125 degree spread in their 134a table and show it bumping into limits when the tables go higher so perhaps he did the math in his head and missed by 10 degrees.

    i assume the spread is a function of having greater latent heat. is that a function of greater density as a liquid, higher heat of vaporization giving coordinately higher enthalpy of condensation, other factors?


  • Eastman
    Eastman Member Posts: 927
    mixed temps

    i wonder what the best way to configure such a system is. if the btu load is dominated by low temp radiant, one would hope for great cops. perhaps two storage tanks, one for each temperature, but then the question is how to control such a setup.
  • jumper
    jumper Member Posts: 1,667
    where am I?

    If most of the time weather isn't too extreme what is the advantage of geothermal? But if I live where there's 2000 hours of bitter cold and another 2000 hours of scorching heat and electricity is expensive,then .....
  • SWEI
    SWEI Member Posts: 7,356
    Seasonal balance

    Roughly equal heating and cooling loads increase the viability and longevity of most ground-source heat pump installations.  If the two are widely disparate, a heat or cold plume can build up, which slowly reduces COP over time.  With sufficient groundwater movement, the problem is masked when the plume shifts to someone else's land.
  • archibald tuttle
    archibald tuttle Member Posts: 810
    interesting point

    no way i'll have as much cooling load. of course i could just pump surface temp or solar heated water during the warm season into the ground loop to improve the transfer of surface temperatures into the ground at that point and stay ahead of that effect.

    still trying to figure out the refrigerant trick.  costwise the 134a and the 410a seem pretty similar but the spread for heating seems better with the 134a.

    and in the slightly more than idle curiosity i'm tryng to figure out why the 134 has a higher spread although a lower cooling capacity (which, as i mentioned on the loads, doesn't matter that much to me. i might do a little cooling just to put heat back in the groun that )
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,217
    PH Chart

    You can find your answer to the refrigerant designs in the PH chart. You should be able to find them with a google search. They are a little difficult to read so you may have to study a bit on that as well.


  • icesailor
    icesailor Member Posts: 7,265
    Moving Groundwater:

    Groundwater is always moving unless it is "Perched Water", which isn't actually "Groundwater". Just water trapped in an impervious bowl. Groundwater is always moving toward you , then away from you. Which direction is the question. The USGS and your State usually have the information. If you find Hydrology maps for your area, you will find higher elevations of groundwater than others. Like everything else, the higher water flows to the lower water. The land elevations and the groundwater elevations are shown above "Mean Sea Level" (MSL).