Joined on February 17, 2005
Last Post on July 13, 2014
@ July 13, 2014 10:18 AM in am i hallucinating or did there used to be a subforum for forced-air furnacesguess this could also go in the air-con forum but i tend to think of furnaces as furnaces even when the burner is off and it is the evaporator is doin' its thang.
older building with nice main feed and return plenums but haphazard branching and branch sizing and couple large returns not well spaced.
and all the ducts are covered upon leaving the boiler room so don't have a lot of access to think about changing a lot of stuff up easily.
so it does 'fine' for heating but struggles to bring enough load and circulation to comfortably cool the same space. figure this is a typical problem although nothing with forced air is typical to me given i spend the vast majority of my time with forced water.
so it occurred to me in the quick fix department that I might be able to slightly improve circulation by increasing the fan speed. I was busy measuring pulleys but didn't measure the squirrel cage itself which was to my recollection maybe 10 to 12" in diameter and 20" long.
my calculations on the current set up was about 900 rpms at the fan. there was a very little bit of adjustment left on a Maska mvl-34 (3 and 1/4" variable width pulley) so i calculate that I raised the rpms to maybe 975 with that. little bit of improvement. so i figured maybe I'd go for an mvl-40 which takes it up to about 3 and 3/4" outside diameter. and if i did the math right i'd come up a little short of 1080 rpms.
But recalling the false performance notion of simply raising steam pressure to 'fix' a steam system, I thought i'd ask besides my emperical results whether noise or vibration are the worse to fear here. figure there is some logical limit to the rpms desirable for these fans.
know there are systems that operate at much higher air pressures for delivery through smaller tubing, but this is on the bubble so i'm just looking for a slight increment.
i feel like this might accentuate the difference in areas served by larger feeds and well served by returns (which wouldn't be all bad as it would indicate the areas that most need ducting attention when they can handle me making some holes, and i'm working on how to get maybe one additional return installed for the toughest area, but the whole place needs a little more umph on cooling. so i'm pretty much convinced to give it a try. i'm goin' in there. wicked witch or no wicked witch. i just want you to do one thing. talk me out of it ???? or not.
@ March 5, 2014 3:30 PM in geothermal vs. airsourcewho'd have thunk it.
actually i kind of understood that and had noticed the distinction in the critical point. what i didnt' know how to read or maybe i didn't have a table, i was getting specific heats at a certain temp in the specs but no sense whether or how much that changed as the temp. of the system changed.
thanks very much for that explanation. i haven't gotten to the you tube yet but i will.
@ March 5, 2014 12:11 PM in geothermal vs. airsourceand i don't anticipate being near the water table even at 10 feet in this location so it would be more a question of whether the extent of cooling of the ground compared to natural conditions would persist through the summer enough to set up the effect SWEI is talking about.
@ March 5, 2014 12:09 PM in geothermal vs. airsourceI may be looking at those charts but I'm not sure. I can find a lot of information about specific properties of refrigerants but i'm not sure how to translate those fixed properties into understanding the amount of latent heat they can carry in a certain set of temperature operating conditions.
@ March 5, 2014 3:36 AM in geothermal vs. airsourceno 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 )
@ March 2, 2014 10:08 PM in geothermal vs. airsourcean 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?
@ March 2, 2014 11:45 AM in geothermal vs. airsourcewe'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.
@ February 24, 2014 10:31 AM in geothermal vs. airsourceEastman,
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.
@ February 23, 2014 10:59 AM in geothermal vs. airsourcecan'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).
@ February 23, 2014 9:18 AM in geothermal vs. airsourceeggroll?
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?
@ February 23, 2014 9:14 AM in geothermal vs. airsourcegot 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?
@ February 23, 2014 8:45 AM in geothermal vs. airsourcei 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
@ February 22, 2014 8:09 AM in geothermal vs. airsourcetony,
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?.
@ February 22, 2014 7:59 AM in geothermal vs. airsourceeastman,
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.
@ February 22, 2014 7:54 AM in geothermal vs. airsourceright, 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.
@ February 20, 2014 2:19 PM in geothermal vs. airsourceso 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'.
@ February 19, 2014 7:50 AM in geothermal vs. airsourceso 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.
@ February 18, 2014 11:11 AM in Which of these two setbacks is more economical?I think we are saying approximately the same thing. I said the efficiency will go down as return water temp climbs. You said efficiency will go up as return water temp goes down.
But, interestingly, his original question about whether to setback temp or setback his curves gets at the point that, short of a perfectly insulated house running water at the desired conditioned room temp, the key decider of needed water temp is the difference between indoor and outdoor temp. And forgetting the condensation point question which has a particular temp or range around a particular temp associated with it, this is really a differential temp question.
So if you lower your curves at night or your target lower indoor temp with a thermostat, that would require lower temp water thus more efficiency. if you raise temps or raise the curves back only to your normal operating, recovery will be slow but efficiency no worse than normal for any given outdoor temp. If you raise them higher for recovery, you lose some efficiency on recovery as Gordy was implying , but i doubt you lose more than you gain. maybe it gets close enough that you won't find convenient equipment with this capacity designed in. But that is different than contending that you actually don't save energy by turning down at night.
I have taken this all by rule of thumb that reducing the difference between indoor and outdoor temp (as in setback) saves more than the temps required for recovery, if one is patient and if condensing is taken out of the equation.
I know that is qualitative and instinctual, not quantitative and scientific. Maybe somebody with the numbers can chime in as to the changes in efficiency over the range of non-condesning return temps and for that matter through the range of partial to fully condensing temps.
But for any given target temp, the advantage of mod is still to prevent short cycling in accomplishing that return temp. . . no?
Don't get me wrong, my instinct is that load matching is a desirable characteristic, just as load matching circulators seem a great innovation. But right now we are paying a pretty serious premium for these technologies and mod has been all but married to con, so folks who could benefit from mod but don't need con are paying for both. Maybe I'm overly fixated on this, and I think the cons will have longer life and need less maintenance in non-condensing use so maybe there is an adequate tradeoff.
This is also maybe epitomized by the long arguments here recently about using on demand hot water heaters as boilers. There you get mod, on the edge of con, regulated by flow, and a price point that works. I know all the boiler manufacturers at AHRExpo were bemoaning the market is too full of competition and they can't get price points with return. To me, boilers seem to cost twice what they should, yet boiler manufacturers aren't making any money. Something is askew here, regulations, liability, I don't know if what all plays into this, but if we got all these people chasing a sweet spot boiler and I'm not finding anyone delivering an entry level 100,000 btu mod con noticeably under 2 grand. I though that was where we were headed but the market seems to moving the opposite direction. Making me wish i could just keep buying the old heatmakers for a thousand bucks and be done with it.
@ February 18, 2014 9:49 AM in geothermal vs. airsourceprobably 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)
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.
@ February 17, 2014 5:54 PM in Which of these two setbacks is more economical?You're right. We don't always make the bottom of our setback if its shoulder season and we don't always make the top of our setups when its friggin cold out, but i set the times involved with a good deal of anticipation.
But insofar as i understand the laws of thermodynamics, the closer the temp. of the conditioned and unconditioned spaces the less the heat loss. ergo you lose less btus when it is cooler inside. and you don't start losing the same amount of btus again until the space is fully out of setback.
yes you spend some input btus coming out, but those inputs are strictly related to what you lost and you lost less when the building was colder.
the key exception would be how the efficiency of your burner responds to different water temps. the obvious is at the low end but if your target temp is above condensing, your system water is not going to be condensing temp except the first pass through when come out of setback.
the main relevance to not setting back, as i understand it, is if you could run at a low mod in condensing mode the whole time, but i just don't think that is as likely with the emitters you have. do you know what temps you run, taken some sample target temps vs. outdoor. is your target keyed to feed or return temp.
the real issue is: can you get much done with 135 deg or cooler water and baseboard?
i run baseboard in half the house with a fairly aggressive reset and doubled element in the larger spaces. the pick up is noticeably slow. its 27 out right now and my return target is 135. so if you have enough element and insulation maybe when its above 25 you're condensing somewhat to more as it gets warmer. but setting back won't take you out of condensing unless your controller sets the curves up for quicker make up.
so you can do a lot of anticipating, start the setback as early as insulation and house characteristics allow, then bring it back at 4 in the morning.
i think the main knock on setback is you can't get that stuff right and outdoor conditions may prevent ideal comfort if you don't recover in time, and with limited savings why bother. On the other hand, I'm not convinced you have a bad idea about just lowering the reset curves if your controller allows you to do that by hours. This could well bring more condensing operation. Mine are not time sensitive.
as far as the mod in mod-con goes, again, i disagree a little bit about where the major efficiency lies. My understanding of thermodynamics here is that the mod alone mostly saves short cycling on less than full load, it doesn't raise efficiency of op without employing condensing mode.
even with low load on a non-mod, it ramps more quickly towards target temp, stack temps are going to be a little higher while the water temp is higher so that is slight loss of efficiency but the assuming same target water temps and modulated fire the boiler is going to run at those less efficient water temps longer. with non-mod it not only goes through the cooler but also the warmer water part of the cycle more quickly.
the issue, it seems to me, might be if the cycle is so short there is a purge and maybe post purge which sends heat up the chimney for maybe 20 or 30 secs total when no heat is being made. so those safety purges are sources of wasting heat and short cycles would add to that waste.
summary, as long as you don't set your curves up for quicker response and undermine condensing, turning the thermostat down saves input btus.
very low temp, hi-mass radiation doesn't change temperature fast enough to make it as logical a candidate for setback, but that is because most of the controller strategies I've seen to date seem to drawn on the steady-states-ville model from europe. but i don't thinnk it is that difficult to imagine a controller hooked up to a little weather station feeding it wind, light/sun as well as temp, and to internet forcecast data that actually sets back low temp hydronic - as well as anticipating effects of those weather condtions on conditioned space temp when not in setback.
@ February 17, 2014 10:14 AM in Pourous copper tubing (?)so they are usually trying to take the water off higher in the boiler and if it is a small replacement without a lot of water in it it can steam or boil and depending on the steam outlets the water level can be uneven in the boiler itself so it may not trip water feeder or low water cut off but you are still airing the pump that is near the top of the 'waterline'.
I lowered the take off on a system i had like this (actually served an indirect hot water heater but same basic idea). problem solved.brian
@ February 17, 2014 10:07 AM in Which of these two setbacks is more economical?are you really running the baseboard under 140 much?
So here is the complication, if you use setback, you actually need to set the reset curve up - ideally it would do this itself automatically by judging the difference between conditioned space temp and conditioned space target temp compared to outdoor temp. so the comeback from the setback will be no condensing except maybe a couple minutes for the first pass of cold water.
to figure out whether steady state operation might be more or close to as efficient, you have to figure out if you are actually condensing and at what outdoor temps and how often you experience those temps.
it is still more btu efficient to turn your heat down at night. sorry for all the eurofinatics out there.
what is your temp. zone, i.e. where do you live? Unless you're super insulated and got uninhibited long walls of all high capacity element or double element, i just don't see you condensing much anyway so setback the thermostat -- my no-radiant areas we use a 10 degree setback (who knew ladies got cheaper to keep with maturity) although you got to have really good insulation and no sheathing air leaks in area of baseboard or run glycol if you're going to do that.
don't know the algorithm on the vitodens. but if it doesn't have conditioned space sensor as part of input and doesn't know you are way below setpoint, it will not adjust curves up so you have to start the recovery much earlier than you need. mine is set for 4 AM so its warm when i roust at 6:30.