|
Keep or Remove Geo?
Last Post 04 Jul 2014 06:42 PM by tamar. 234 Replies.
|
Sort:
|
|
Prev Next |
You are not authorized to post a reply. |
|
|
waterpirate
Basic Member
Posts:467
|
23 Mar 2013 05:47 PM |
|
Given the fact that your house is unique and a grand old dame. Prior to turning the geo back on I would get a energy audit done by an audit company includeing a blower door test, and infiltration data. That information will be priceless for you moveing forward to do repairs to yoUr envelope and your system. Eric |
|
Eric Sackett<br>www.weberwelldrilling.com<br >Visit our Geothermal Resource Center! |
|
|
joe.ami
Veteran Member
Posts:4377
|
25 Mar 2013 08:11 AM |
|
If they are on board to make it right by you, then give them a deadline by which time you want the system to function correctly or....... |
|
Joe Hardin www.amicontracting.com We Dig Comfort! www.doityourselfgeothermal.com Dig Your Own Comfort! |
|
|
tamar
Basic Member
Posts:128
|
25 Mar 2013 08:41 AM |
|
Posted By joe.ami on 25 Mar 2013 08:11 AM
If they are on board to make it right by you, then give them a deadline by which time you want the system to function correctly or.......
I'm not even sure what would make it right at this point. When the new TXV finally arrived after 3 weeks in near 100 degree heat last summer, we thought that was the end of it, then we continued to have erractic system behavior; and they pulled wires and installed a hard wired thermostat, then we thought that was the end of it. Now, today, the tech is installing a new blower motor and in the Spacepak and a temp sensor valve that will do something for the hi-temp WTW (which has been "out of the loop" since the new stat was installed). We always hope the next visit will make it right. |
|
|
|
|
tamar
Basic Member
Posts:128
|
25 Mar 2013 09:32 AM |
|
We now have a new Spacepak blower motor. Apparently as failed motor neared its end-of life, it was drawing 7amps. New blower motor is drawing 2 amps.
The tech was here for 6 hours. I am cautiously optimistic that things will be better. It is now sunny and warm, so we are not currently adding to our heating bill.
|
|
|
|
|
joe.ami
Veteran Member
Posts:4377
|
29 Mar 2013 11:27 AM |
|
Well? How goes? |
|
Joe Hardin www.amicontracting.com We Dig Comfort! www.doityourselfgeothermal.com Dig Your Own Comfort! |
|
|
tamar
Basic Member
Posts:128
|
29 Mar 2013 01:57 PM |
|
Posted By joe.ami on 29 Mar 2013 11:27 AM
Well? How goes?
Thank you for asking. Our kitchen remodel architect, who recommended this hvac installer (did I mention we did the geo install and the kitchen remodel in tandem?) is "mediating" for us. I called him and asked him to step in to help us get to a resolution. He has had several conversations/emails with the installer, some of which I haven't been privy to, and the net-net is we are going to meet Thursday at which time we're going to hopefully hear a plan to "significantly reduce our utility costs" (in the words of the architect). The installer is supposedly doing some research now. The tech who was out here replacing the blower motor alluded to a recommendation they'd received from someone they were talking to about amount of droop allowed before gas kicks in and also modifying the delay before the auxiliary heat kicks in. In the meantime, the SpacePak is running quietly (it seems more quiet than even when it was brand new) and the house is very comfortable. Per the recommendations in this thread, I'm also looking into ways to tighten up the house, though at this point I will wait to not confuse the calculations. We just got our Feb 22-March 25 Xcel bill. March 25 was the day the SpacePak motor was replaced, so this bill is pretty much our "heat with gas" bill. Our gas usage on the bill is listed as 249 ccf x 1.0245 (heat content adjustment) = 255 therms. Total cost to heat our house for 29 days with an average temp of 27 degrees = $193.88 (all in, taxes and base charge included). I think we can do the math and use that as a baseline to see if our installer can make the Geo cost-efficient. FWIW, our geo-only meter read 30 kWh for the month. About 10 days ago it was @ 4 kWh for the month (I checked to see if it was drawing electricity with the system not in use). The display on the high-temp W2W was on, which I assume accounts for the slight draw and indicates nothing seriously out of whack with the geo not heating the house. Did I do the previous BTU calculation correctly? Just want to let you know, I really appreciate all the advice and it's made me much more confident about knowing when we are being given good vs questionable information. Thanks! |
|
|
|
|
Dana1
Senior Member
Posts:6991
|
02 Apr 2013 03:08 PM |
|
(I've been away, and might have jumped in earlier, but here goes...) Assuming a base 65F balance point and that the 29 days was truly all gas, and to make up for the overnight setbacks and period where it stagnated in the mid-60sF for a room temp, let's assume it really hits the 96% DOE efficiency on the boiler (which it might, if you have a lot of radiation and the output temp stays below 125F even at 0F outdoor temps)... 65F - 27F= 38 HDD average per day 255 therms / 29 days = 879,310 BTU per day source fuel or 879,310 BTU x 0.96= 844,138 BTU /day net which for 38 HDD/day-avg is 844,138 BTU/ 38 HDD= 22,214 BTU/HDD which is (22,214 BTU/24 hours=) 926 BTU/ degree hour. <<< That's the slope of your heat load. Assuming a design temp of -10F and a balance point of 65F, the design heat delta-T is 65F - (-10F)= 75F Which means your design heat load is on the order of 75F x 926= 69,450 BTU /hr ... which is a heluva lot less than the 98,122 BTU/hr at a 65F delta cited in the original heat load calc, eh? Even if you put docjensers fat thumb on the scale and use 72F as the zero point (on a slope derived from a 65F zero) that's still an 82F delta for (926 btu/degree-hr x 82F= ) < 76,000BTU/hr. Comparisons an a BTU per square foot of conditioned space are ridiculous, even for new housing, since it varies SO much from design to design. The BTU/foot number at the 99% condition is really only important to radiant floor heating designs, since that ultimately determines the peak water temps (and thus the net efficiency possible) of the system. The 30 kwh burned up by an idling geo system during the time period only adds about a therm to the total, so it's a sub-1% error. If it in fact was running for that 30kwh (might have been), call it 300,000-400,000 BTUs,which adds only 500-600BTU/hr to the average, so maybe that ~69,450BTU/hr is really closer to70K? OK call it 70K. (Does it really matter? ;-) ) It's really less than 76K any way you slice it, so 70-75K (or less) is really the ball park you're looking at for a 99% heat load, not 95-100K+, and it wouldn't surprise me if a more careful measurement of the balance point & slope & boiler system-efficiency came it at something closer to 60K, but under that is unlikely. Peeling off a half ton (or even 1.5 tons) in an 1890s Victorian is usually pretty straightforward with blower-door w/ IR-imaging-directed air sealing & spot insulation. Taking it down even more might still be cost effective, but it would have been more cost-effective had it been done prior to installing the geo, since it would have been reducing the geo's size & cost. But now that it's already in and paid-for (assuming you can get it to run reliably & efficiently with whatever design fixes to the system that may be in order), the net cash return in of lowering the load drastically further isn't quite as much, since the financial hit of the up-sized geo is already on the books. There's always a comfort argument to lowering the heat load too- highly efficient buildings are usually more comfortable than highly efficient HVAC systems at any given room temp (with the possible exception of radiant floor heating.) It's always worth plucking all the low-hanging fruit you can, while keeping an eye on what be on the next higher branches, for a "maybe, someday" comfort enhancement, even if the net-present-value on kwh savings doesn't necessarily come out in positive or neutral numbers in short years. (High performance windows are usually in that latter category, but DO make a real comfort difference at 8AM when it's in negative-digits outside.)
|
|
|
|
|
tamar
Basic Member
Posts:128
|
02 Apr 2013 05:46 PM |
|
We are 8 days post-install of the new SpacePak blower motor, and the geo has used 709 kWh, which seems high to me (or at least no lower than it was in January). That's a disappointment; I guess hope springs eternal.
Our meeting with the installer and our architect is on Thursday.
(And I understand we play a part in getting our energy usage down; we will find the low hanging fruit and make some changes. I've already gotten the name of someone who can help with the basement insulation.)
|
|
|
|
|
FrankZ
New Member
Posts:6
|
03 Apr 2013 11:43 PM |
|
Hi, I just came across your posts today in an almost completely futile search for any info at all on performance of the 50YEW high-temp hydronic unit, because ever since I heard about it, I've been looking into using it as you did, with my existing radiators. Judging from your experience, I'd guess you'd tell me to stay away from it, but my situation is a little different because we have done a lot of insulating (Argon-filled double-glazed gasket-sealed casement windows, wall cavities foamed-in-place), so at this point my radiators are almost ludicrously oversized. It's also a smaller house ~1300sf with 7-1/2' ceilings, in a milder climate (central Virginia), with a higher earth temp (60°F), so I really do think it would work if the unit performed anywhere near spec. But you seem to be saying it doesn't even work reliably, which I'm sorry to hear. As far as your own situation, I would say that expecting to save a bundle with geo instead of gas is asking a lot especially in your climate. With the current glut from all that fracking, gas is dirt cheap, from your bill you are only paying 76 cents a therm, is that right? A therm is 100,000 Btu so let's say 96,000 of actual heat, which is about 28 kWh. So if your average COP is 2.48 as predicted in the workup, that much heat would require an input of 11 kWh into the geo system. I don't know your rate, but say it's twelve cents a kWh, then it would cost $1.21, significantly more than gas. You say you were using 844,000 Btu a day of gas heat, so that's about 250 kWh, which would be predicted to require about 100 kWh a day input for the geo system, which is about what you're using. The bottom line is that at current prices it's going to be very difficult for any geo system even working optimally, to beat the cost of gas and a condensing 97% efficient boiler. You'd need to get the COP well above 3, which just might be impossible in a situation with special challenges such as the need to move so much air up three 10-foot storys through retrofitted ducts, which is going to take a significant amount of power in itself. Oil (which I have) is a different story because it costs three times as much. As far as staging of the hydronic vs forced air, your system is 8 tons - the model 64 forced air is 5 tons of that and the hydronic 50YEW is only 3 tons (it only comes in one size). In fact, with 40ºF entering source temperature, it's only rated to put out about 27,000 Btu/hr at 120ºF load temp (which is about the lowest temp at which you're going to get significant heat from radiators), so it's not at all surprising that it can't do the job by itself as soon as the outside temp hits 30ºF. Another point is that from what I've read, it has its own internal preprogrammed control microprocessor with limited options for user adjustment. It doesn't seem to be designed to be "slave" to an integrated control system that includes another unit, so I'm guessing that any such system would involve a good deal of improvisation. The good news is that as you add insulation, the savings in geo operational costs should be more than proportional because in addition to needing less heat, the heat has to be pumped up less of a temperature gradient - the temperature of the radiators and the forced air heat can both be lower and the field loop temperature will be a little higher. So a 10% reduction in heat loss might give 20% or so savings in power input, and the relative advantage of geo over gas will increase. |
|
|
|
|
joe.ami
Veteran Member
Posts:4377
|
04 Apr 2013 08:19 AM |
|
Frank, If you wish to get involved with high temp WTW, best to do a very good job of vetting your installer. Tamar seems to have picked a dealer with much experience in geo, but that doesn't make them a hydronic savvy. |
|
Joe Hardin www.amicontracting.com We Dig Comfort! www.doityourselfgeothermal.com Dig Your Own Comfort! |
|
|
tamar
Basic Member
Posts:128
|
04 Apr 2013 09:18 AM |
|
Posted By FrankZ on 03 Apr 2013 11:43 PM
Hi, I just came across your posts today in an almost completely futile search for any info at all on performance of the 50YEW high-temp hydronic unit, because ever since I heard about it, I've been looking into using it as you did, with my existing radiators. Judging from your experience, I'd guess you'd tell me to stay away from it, but my situation is a little different because we have done a lot of insulating (Argon-filled double-glazed gasket-sealed casement windows, wall cavities foamed-in-place), so at this point my radiators are almost ludicrously oversized. It's also a smaller house ~1300sf with 7-1/2' ceilings, in a milder climate (central Virginia), with a higher earth temp (60°F), so I really do think it would work if the unit performed anywhere near spec. But you seem to be saying it doesn't even work reliably, which I'm sorry to hear. As far as your own situation, I would say that expecting to save a bundle with geo instead of gas is asking a lot especially in your climate. With the current glut from all that fracking, gas is dirt cheap, from your bill you are only paying 76 cents a therm, is that right? A therm is 100,000 Btu so let's say 96,000 of actual heat, which is about 28 kWh. So if your average COP is 2.48 as predicted in the workup, that much heat would require an input of 11 kWh into the geo system. I don't know your rate, but say it's twelve cents a kWh, then it would cost $1.21, significantly more than gas. You say you were using 844,000 Btu a day of gas heat, so that's about 250 kWh, which would be predicted to require about 100 kWh a day input for the geo system, which is about what you're using. The bottom line is that at current prices it's going to be very difficult for any geo system even working optimally, to beat the cost of gas and a condensing 97% efficient boiler. You'd need to get the COP well above 3, which just might be impossible in a situation with special challenges such as the need to move so much air up three 10-foot storys through retrofitted ducts, which is going to take a significant amount of power in itself. Oil (which I have) is a different story because it costs three times as much. As far as staging of the hydronic vs forced air, your system is 8 tons - the model 64 forced air is 5 tons of that and the hydronic 50YEW is only 3 tons (it only comes in one size). In fact, with 40ºF entering source temperature, it's only rated to put out about 27,000 Btu/hr at 120ºF load temp (which is about the lowest temp at which you're going to get significant heat from radiators), so it's not at all surprising that it can't do the job by itself as soon as the outside temp hits 30ºF. Another point is that from what I've read, it has its own internal preprogrammed control microprocessor with limited options for user adjustment. It doesn't seem to be designed to be "slave" to an integrated control system that includes another unit, so I'm guessing that any such system would involve a good deal of improvisation. The good news is that as you add insulation, the savings in geo operational costs should be more than proportional because in addition to needing less heat, the heat has to be pumped up less of a temperature gradient - the temperature of the radiators and the forced air heat can both be lower and the field loop temperature will be a little higher. So a 10% reduction in heat loss might give 20% or so savings in power input, and the relative advantage of geo over gas will increase.
Frank, it sounds like you've done your homework, and already know more about the equipment than I do. I would say that the oversized radiators are not your friends. One of our earliest observations was that as soon as there was a call for heat, the temp in our buffer tank dropped from ~125 into the 70s. Before it could recover the gas was kicking in (this is how I remember it from 2 years ago, the system has been rewired several times since then, and I was not aware that detailed notes would come in handy, but I'm pretty sure that was one of our early experiences. Distressing to us because of those "only on the coldest days" comments we'd heard about needing our back-up heat). Our installer was talking in layman's terms and told us that the WTW would be 2x as efficient as a traditional gas heating system, but WTA (water to air) would be 5x as efficient. We liked radiator heat and initially thought he was saying we'd be saving money, just not as much. I will report back with the results of this evening's meeting of the minds. |
|
|
|
|
joe.ami
Veteran Member
Posts:4377
|
04 Apr 2013 11:45 AM |
|
"One of our earliest observations was that as soon as there was a call for heat, the temp in our buffer tank dropped from ~125 into the 70s. " Whoa.......that needs to be handled by more buffer water or plumbing not wiring. If you have significant down time on the geo (time when it's not running) it could be making more hot water (to delay boiler fire up) further back-up boiler could be plugged in downstream of the boiler to let them run simultaneously. Giant radiators are actually beneficial to lower temperature systems (more btus with lower temps). |
|
Joe Hardin www.amicontracting.com We Dig Comfort! www.doityourselfgeothermal.com Dig Your Own Comfort! |
|
|
tamar
Basic Member
Posts:128
|
04 Apr 2013 01:46 PM |
|
Posted By joe.ami on 04 Apr 2013 11:45 AM
"One of our earliest observations was that as soon as there was a call for heat, the temp in our buffer tank dropped from ~125 into the 70s. " Whoa.......that needs to be handled by more buffer water or plumbing not wiring. If you have significant down time on the geo (time when it's not running) it could be making more hot water (to delay boiler fire up) further back-up boiler could be plugged in downstream of the boiler to let them run simultaneously. Giant radiators are actually beneficial to lower temperature systems (more btus with lower temps).
I am looking back at the emails chains from that first winter, and this probably was during the time before the faulty sensor was replaced. When I go down to look at the system now, the buffer tank reading displayed on the screen of the hi temp unit says it is 65 degrees. I believe the installer disconnected it because we expressed concern about it and either our concern was misplaced or he was tired of hearing about it. Not sure which. We've got a 40 gallon buffer tank that is hand labeled as being for summer aux hot water, a 50 gallon hot water heater, an 80 gallon Phoenix boiler, and the WtW hi-temp geo unit. It was the display on the high temp unit that dropped so fast on a call for heat. I do not understand why we have all these tanks, so I guess that's one of the things I need to ask tonight. I must still be in the GHW heating mindset for the radiators....I think about them as being slow to heat up and slow to cool down. At lower temps, I was thinking they'd be even slower to heat up, so harder to maintain the temp if they don't run almost constantly. |
|
|
|
|
tamar
Basic Member
Posts:128
|
04 Apr 2013 08:08 PM |
|
As promised, I am checking back in after the meeting with the installer. The net-net is that we are going to pull the breaker on the WtW hi-temp unit, as it is more expensive to run than our gas boiler given current electric and gas prices. If electricity ever gets cheaper, or natural gas more expensive, then we can re-evaluate.
He presented us with a chart that shows C.O.P. at different $/kWh, and AFUE at different $/ccf. Here is what I took away from the discussion of this chart:
If we run both WtA and WtW geo at a combined C.O.P. of ~250%, with our electricity at .07/kWh we are paying $8.20 cpm btu's. If we pull the breaker on the WtW and just run the WtA geo, he stated our C.O.P. would be more like 350% and we will pay $5.86 cpm btu's. Using 92% for our AFUE, and $/ccf of .70, the cpm btu's for heating with gas is $7.61
So, the WtA geo is most efficient, and we will run that as our first stage (or first 2 stages, he couldn't tell us). Next (which might be stage 2 or might be auxiliary) will be the gas boiler. It will be called into service if any of the below are true: 1. there is a 3 degree droop 2. the call for heat isn't satisfied w/in 45 minutes 3. the temp outside is <15 degrees
We talked about the lack of reliability of the SpacePak. I asked how much more could go wrong, and apparently the only thing that hasn't been replaced is the circuit board. The TXV, which is soldered to the coil, was replaced last summer and now the blower motor is new.
Our one additional area of potential savings is if the system without the W2W does not need 3 pumps. The installer left with a "to do" to analyze whether or not that third pump is still needed. He said it likely costs $80-$100 year for the pump, and some rewiring would be needed because it is wired in line.
Does this all sound right?
|
|
|
|
|
joe.ami
Veteran Member
Posts:4377
|
05 Apr 2013 09:51 AM |
|
Sounds about right. Still not convinced that system is set-up correctly, but I think the boiler is likely your better heat plant at this time. |
|
Joe Hardin www.amicontracting.com We Dig Comfort! www.doityourselfgeothermal.com Dig Your Own Comfort! |
|
|
FrankZ
New Member
Posts:6
|
08 Apr 2013 12:29 AM |
|
I'd agree, that sounds like a reasonable plan, and at 7 cents a kWh you might actually save some money. Of course when they said the hydronic would be twice as efficient as gas, they were talking per unit energy not per dollar. But I think the failure of the hydronic is mainly one of the controls. It's not at all surprising that the buffer tank would drop to the 70s when the hydronic first goes on. Every radiator is going to have several gallons of 65-degree water, and together that's several times as much water as is in the buffer tank, and that's not even counting several thousands pounds of thermal mass in the radiators themselves. When the circulator goes on, it's all going to be mixed, and average water temperature including the buffer tank is going to be close to room temperature.
When set up properly, geo hydronic is nothing like a boiler system, where you get periodic calls for heat, the circulator goes on, the gas heats the water, the radiators get hot, then cool down gradually until the next call for heat. Instead the geo hydronic should maintain the radiators at an almost constant temperature that is adjusted based on the outside temperature sensor and is calibrated to give off just enough heat constantly to maintain the desired room temperature. This is what the microprocessor in the 50YEW is designed to do. If the heat periodically goes off and on, it means the radiators are getting hotter than they need to get and COP is lower than it could be. Yes, when you first turn it on, it's going to take a long time - probably several hours - to reach equilibrium, but after that it should be work pretty efficiently, provided there is enough radiator surface area, and the more the better. If the radiators never get warm even after hours of running the hydronic unit, it means the heat pump didn't have adequate capacity to heat the space in the first place, not that the radiators were too big. The mistake, in my opinion, was wiring the gas to come on just because the buffer tank temperature dips. Instead, gas should kick in based on low outside temperature, or else be controlled manually.
As far as the loop pumps, I'd suggest leaving them both connected because you should still use the whole 1800 ft of loop even though it's now oversized. The more loop you use the higher the loop temperature will be, and even a few degrees higher EWT from the loop will improve COP, probably enough to more than compensate for the power needed to run the extra pump.
|
|
|
|
|
FrankZ
New Member
Posts:6
|
08 Apr 2013 07:53 AM |
|
Thanks, good advice I'm sure. It really is amazing the range of stories you hear. Some people put it in, turn it on, save a bundle every year, never have a problem. Others have the installers back every few months for years trying to get it right till they finally give up, leaving a $30,000 system that they don't even use. It's terrifying actually.
I do have A/C ducts that I could use for forced air, but they're all in the ceiling and they run through an unheated attic, so there would certainly be some loss of efficiency there, but maybe still a lot more efficient than trying to do hydronic with radiators, based on Tamar's experience.
|
|
|
|
|
joe.ami
Veteran Member
Posts:4377
|
08 Apr 2013 08:15 AM |
|
"As far as the loop pumps, I'd suggest leaving them both connected because you should still use the whole 1800 ft of loop even though it's now oversized. The more loop you use the higher the loop temperature will be, and even a few degrees higher EWT from the loop will improve COP, probably enough to more than compensate for the power needed to run the extra pump." Whether you disconnect a pump or not will not increase or decrease the amount of loop you use, it only changes the GPM. If you have a 3 ton split or smaller, one pump is fine.
|
|
Joe Hardin www.amicontracting.com We Dig Comfort! www.doityourselfgeothermal.com Dig Your Own Comfort! |
|
|
tamar
Basic Member
Posts:128
|
08 Apr 2013 08:55 AM |
|
Posted By joe.ami on 08 Apr 2013 08:15 AM
"As far as the loop pumps, I'd suggest leaving them both connected because you should still use the whole 1800 ft of loop even though it's now oversized. The more loop you use the higher the loop temperature will be, and even a few degrees higher EWT from the loop will improve COP, probably enough to more than compensate for the power needed to run the extra pump." Whether you disconnect a pump or not will not increase or decrease the amount of loop you use, it only changes the GPM. If you have a 3 ton split or smaller, one pump is fine.
We currently have 3 loop pumps in line. The original design (and pricing) called for 2 pumps, but they added a third. I guess I should really dig into why the third was added. |
|
|
|
|
tamar
Basic Member
Posts:128
|
08 Apr 2013 09:00 AM |
|
Posted By FrankZ on 08 Apr 2013 07:53 AM
Thanks, good advice I'm sure. It really is amazing the range of stories you hear. Some people put it in, turn it on, save a bundle every year, never have a problem. Others have the installers back every few months for years trying to get it right till they finally give up, leaving a $30,000 system that they don't even use. It's terrifying actually.
I do have A/C ducts that I could use for forced air, but they're all in the ceiling and they run through an unheated attic, so there would certainly be some loss of efficiency there, but maybe still a lot more efficient than trying to do hydronic with radiators, based on Tamar's experience.
It really is shocking to me that geo is not saving us money. We wouldn't have done it if there hadn't been the big tax break to encourage us to go that way. We did not have air conditioning before, so this is really just like a really expensive air conditioning retrofit for us. I cannot complain about the comfort when the geo is working. I am hoping moving air through the basement also mitigates a slight radon problem we had (I was told it would; of course I was told a lot of things). |
|
|
|
|
You are not authorized to post a reply. |
|
Active Forums 4.1
|
Membership: |
|
Latest:
PhoenixStucco |
|
New Today:
1 |
|
New Yesterday:
1 |
|
Overall:
34716 |
|
People Online: |
|
Visitors:
97 |
|
Members:
0 |
|
Total:
97 |
|
|
|