chadws
New Member
Posts:5
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| 17 May 2009 06:29 PM |
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I'm currently building a house and am losing a little faith in my geo guy the more I educate myself. I live close to Edmonton, AB so heating needs are the priority. The house we are building has 2,200 sq ft. on the main a 2,200 sq ft. walkout basement and a 1,300 sq ft. upper floor. I've actually had a heat loss calc. done for me using an outside design temp of 12F which shows 66,000 BTU's/HR. We have approximately 30 days a year that have a mean temperature colder then 12F. So, here's what we've had done so far:
1) Two 300' trenches 8-10 feet deep 16' wide with eight loops in each trench of 3/4". The soil is primarily clay and on the drier side. I'm not sure how well the backfill was compacted.
2) My geo guy is recommending two three ton units from the following units http://www.nextenergy.ca/pdf/products/THW/THW_Brochure.pdf
Questions are as follows:
1) Do I have enough/too much pipe? Can you have too much? Am I too deep?
2) Do the units recommended seem reasonable? I don't want to oversize.
3) Is the EWT acronym used to describe the temperature coming from the ground?
4) I've been told that most geotherml units are rted for cooling and need to be derated to calculate heating. Would this be the case with these?
Great forum. Appreciate any help I can get as stress of going with geothermal is starting to rise!
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TechGromit
Advanced Member
Posts:535
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| 17 May 2009 09:23 PM |
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Posted By chadws on 05/17/2009 6:29 PM
I'm currently building a house and am losing a little faith in my geo guy the more I educate myself. I live close to Edmonton, AB so heating needs are the priority. The house we are building has 2,200 sq ft. on the main a 2,200 sq ft. walkout basement and a 1,300 sq ft. upper floor. I've actually had a heat loss calc. done for me using an outside design temp of 12F which shows 66,000 BTU's/HR. We have approximately 30 days a year that have a mean temperature colder then 12F. So, here's what we've had done so far:
1) Two 300' trenches 8-10 feet deep 16' wide with eight loops in each trench of 3/4". The soil is primarily clay and on the drier side. I'm not sure how well the backfill was compacted.
2) My geo guy is recommending two three ton units from the following units http://www.nextenergy.ca/pdf/products/THW/THW_Brochure.pdf
Questions are as follows:
1) Do I have enough/too much pipe? Can you have too much? Am I too deep?
2) Do the units recommended seem reasonable? I don't want to oversize.
3) Is the EWT acronym used to describe the temperature coming from the ground?
4) I've been told that most geotherml units are rted for cooling and need to be derated to calculate heating. Would this be the case with these?
Great forum. Appreciate any help I can get as stress of going with geothermal is starting to rise!
1. I don't know about enough, but You can never have too much pipe, and you can never be too deep. 2. I'm not an expert, but two 3 ton units for 66k BTU sounds about right to me. 3. Yes, EWT is Entering Water Temperature, the water returning from your close loop field. 4. I believe the exact oppose is true, Geothermal systems are rated for heating and need to be derated for cooling, the fact that the the cooling season generally uses 2/3 the amount of power then heating supposes this. But than again, I guess it would depend on were you live, I'm sure people south of texas have a lot more cooling days than heating.
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engineer
Veteran Member
Posts:1495
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| 18 May 2009 07:20 AM |
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Is 12 deg F the correct oudoor design temp for Edmonton?
I'd think -12 F would be closer to the mark, and that's a HUGE difference!
Get this right before you proceed with any system selection |
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Curt Kinder
Absent data, you have only an opinion.
www.hoviscustombuilders.com
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engineer
Veteran Member
Posts:1495
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| 18 May 2009 07:48 AM |
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I just checked my RHVac design software. It has a -25 F winter design temp for Edmonton.
Just to give you an idea of how far off 12 F would be, winter design temps of 12 are found in states such as Tennessee or Virginia
Don't confuse mean temperature with design temperature.
I repeat, get this right before going any further. |
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Curt Kinder
Absent data, you have only an opinion.
www.hoviscustombuilders.com
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Bergy
Basic Member
Posts:144
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| 18 May 2009 07:49 AM |
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According to my Uponor ADS program, Edmonton's design temp is -23*!!!!
Engineer is 100% correct... If the numbers are not correct, the system will not perform as needed.
Bergy
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joe.ami
Veteran Member
Posts:1652
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| 18 May 2009 07:58 AM |
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Posted By chadws on 05/17/2009 6:29 PM
I'm currently building a house and am losing a little faith in my geo guy the more I educate myself.
I'm not so sure. Why do you think there is a problem?
I ran you through design software and the pipe seems adequate and the heat pump size is designed around 95% of the heating requirement.
2) My geo guy is recommending two three ton units from the following units http://www.nextenergy.ca/pdf/products/THW/THW_Brochure.pdf
These are Climatemaster units and they are fine.
3) Is the EWT acronym used to describe the temperature coming from the ground?
Entering water temperature to the heat pump, heat exchanger. LWT would be water leaving the heat pump and the difference is the Delta T. You can also measure ent. and leaving water temps on a desuperheater loop or the load side of a water to water heat pump. Ent. and leaving (EAT,LAT) air temperatures might be measured on the load side of a water to air heat pump.
4) I've been told that most geotherml units are rted for cooling and need to be derated to calculate heating. Would this be the case with these?
Yes, that would be the case with these and most any other system out there.
Great forum. Appreciate any help I can get as stress of going with geothermal is starting to rise!
So far I haven't seen anything that makes me suspect your guys are anything but pro's. Requirements are different in your neck of the woods than mine. I looked at the bin reports and .....burrr. Unless you have something else that makes you worry, I suspect you might be a victim of comparing yourself to applications south of you and it would throw you (we would use 4 tons for your heating load around here).
Good Luck,
Joe
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Just a Mechanic;
Geothermal; Savings Underfoot |
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chadws
New Member
Posts:5
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| 18 May 2009 01:44 PM |
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Engineer and co. excuse my ignorance on this subject as I'm sure that I'm confusing a few different concepts. At -24F wouldn't I end up oversizing my units? This would represent less than a weeks worth of weather for us, and yes it is a very cold week! I think the coldest average temperature for us was 12F or -12C. Do you use a design temp that represents the coldest weather and then take a percentage of the btu's/hr? Given we have such extreme weather for a small period of time wouldn't this result in oversizing? Also, given we have such wide swings in temperature, not uncommon to go from -25F to 12F in a day do you think it might make more sense to go skip hydronic and go forced air? Finally, joeami is there a rule of thumb for derating these units?
Thanks ... I'm getting there one tiny step at a time!
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engineer
Veteran Member
Posts:1495
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| 18 May 2009 03:13 PM |
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Do not design for average daily temperature or else the system will be way undersized during cold nights unless you have a thermally massive home.
Design temp is generally such that 97.5% of hours are at or above it. 2.5% of hours are below design temp during a typical season. If you have solid reason to believe your "micro climate" is substantially warmer from the city's design temp then go with your specific data.
Actual unit capacity vs nominal tonnage depends on the specifics of each installation - the primary variables are temperature, and to a lesser extent, flow of the ground source water. Those values in turn depend on location and loop design. Manufacturers provide extended performance tables detailing each model's capacity for various conditions of loop temperature and flow. It is from those tables the loop design, and the house load that proper unit tonnage is selected.
I've been to Edmonton in November, and I recall it already being in the teens at night, a full month shy of winter. I left as soon as I could... |
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Curt Kinder
Absent data, you have only an opinion.
www.hoviscustombuilders.com
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Bergy
Basic Member
Posts:144
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| 18 May 2009 03:31 PM |
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Chad,
Heating systems are designed to provide the required amount of Btu's/hr AT design temp. You can under-size your Geo but that has to be made up by the electric strip, or some other means. Why run the electric strip @ 100% efficient when the Geo will run @ 300~400%? We generally design the system so the TWO STAGE heat pump will provide 93~97% of the required Btu's/hr with Aux electric strip making up the difference. This helps control the amount of cooling Btu's available.
One of the highest rated 3 ton units (GeoComfort GT036) will provide 31,400 Btu's/hr @ 30* EWT. One of the lower rated units (Waterfurnace ND038) will provide 27,000 Btu's/hr @ 30* EWT. Those same units, in cooling provide 39,400 Btu's/hr and 40,200 Btu's/hr respectivley. (Running in second stage)
You can see that even though a "3 Ton" unit is installed, You do not get "3 Tons" (or 36,000 Btu's) of heat out.
Bergy
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joe.ami
Veteran Member
Posts:1652
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| 18 May 2009 09:29 PM |
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Did my homework on info you provided and it seemed to support your installer. I would yield to the local contractor anyway but find nothing that compels me to dispute the design you described. Again I'm curious as to the specific reasons you've lost faith in your guy.
J |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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chadws
New Member
Posts:5
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| 19 May 2009 12:30 AM |
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Main reason I've lost faith is because I don't think he actually did a heat loss calculation! He's never asked me for any information on how I'm finishing the house, so even if he has done a calculation it's probably pretty vague at best. Also, he did the neighbours across the street and they've had some horrendous electric bills. Granted they also installed a hydronic system themselves which could account for a lot.
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joe.ami
Veteran Member
Posts:1652
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| 19 May 2009 07:11 AM |
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I confess I missed the THW in your original comments. I do not yet have operating software on that system. As others already mentioned the disparity between heating and cooling btu's is case by case. The THW I believe only has one size that is 32,500.
If you are still unclear, when I said 95% of the load, that means 95 out of 100 winter days the system will not require auxiliary. What are you using for back-up (aux) heat?
Did the installing contractor have a copy of blue prints for your new home?
Would not wish to encourage you to change from radiant if that's what you want. Pro's and Con's to every system.
When you say your neigbors had a high electric bill can you give us an example in KW's?
j |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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engineer
Veteran Member
Posts:1495
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| 19 May 2009 07:48 AM |
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Chad,
In a PM you asked about design temp for Ketchikan, AK, theorizing that your design data originated there. My S/W lists a 20 deg F winter design temp for Ketchikan - suprisingly mild for such a northern latitude, but Alaska has huge climate variation. Fairbanks design temp is -47, as an example of the other extreme.
I completely agree with Joe's advice to size a geo system for 95% NOT 100% of design day load, just get the design temperature correct.
I know I'd want radiant in a northern climate. |
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Curt Kinder
Absent data, you have only an opinion.
www.hoviscustombuilders.com
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joe.ami
Veteran Member
Posts:1652
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| 20 May 2009 06:34 AM |
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Did the installing contractor have a copy of blue prints for your new home?
When you say your neigbors had a high electric bill can you give us an example in KW's?
Had one other question. When you said 8 loops per trench, did you mean slinkies or 8 individual pipes? j |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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jonr
Advanced Member
Posts:545
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| 20 May 2009 09:40 AM |
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Most cost effective will be more like 75% of design BTU and this will cover about 95% of your heating.
If he can't supply both of these numbers, I would find someone else.
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chadws
New Member
Posts:5
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| 20 May 2009 12:40 PM |
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Thanks Engineer .... I hadn't had time to review Ketchikan's weather and give the company doing my heat loss calc a proper comparison as my town doesn't show up in ASHRAE data. We've since adjusted to Edmonton and heat loss now shows 107,000 btu's/hr ..... and it snowed yesterday! Joe, I'm not sure what you mean by slinky but we have 8 pipes leaving the house and running straight for 300 yards and then returning. So, across the two seperate trenches we have approximately 9,600 feet in pipe. When we dug the trenches the geo guy measured the temperature of the ground and it was approximately 54F , and after talking to my father-in-law who actually excavated for us we were actually 12 feet down in some places. I was looking at Hydronic but with the increased heat load I'd need supplemental heat in quite a few rooms. Hard to imagine two 3 tonne units will work .... now I'm really starting to be concerned with my geo guy. |
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joe.ami
Veteran Member
Posts:1652
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| 20 May 2009 11:13 PM |
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umm, I don't know what to say until we determine wether your heat loss is 66 or 107K.
j |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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engineer
Veteran Member
Posts:1495
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| 21 May 2009 07:29 AM |
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It sounds to me like your geo guy needs the updated design heat load info. Ideally he has his own heat load software and will know what design temperatures are appropriate for your area. I'm a bit concerned he didn't catch the +12 deg design in the first place.
Boots on the ground at your site are (or at least should be) much more relevant and accurate than free internet advice from a guy in Florida.
The proper house load will drive both geo tonnage selected AND loop field design. If the Ketchikan design temp drove the loop design then you may not have enough pipe in the ground. |
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Curt Kinder
Absent data, you have only an opinion.
www.hoviscustombuilders.com
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joe.ami
Veteran Member
Posts:1652
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| 21 May 2009 08:28 AM |
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Posted By engineer on 05/21/2009 7:29 AM
It sounds to me like your geo guy needs the updated design heat load info.
We don't know that. We don't know yet if his guy has done a load calc.
Ideally he has his own heat load software and will know what design temperatures are appropriate for your area. I'm a bit concerned he didn't catch the +12 deg design in the first place.
I took the time to check the requirements based on the first loss calc Chad gave us (using Edmonton as the closest major town as indicated)and found the design was probably ok. What do you know that I don't (aside from the fact that the load is suddenly most of twice as much)?
Boots on the ground at your site are (or at least should be) much more relevant and accurate than free internet advice from a guy in Florida.
The proper house load will drive both geo tonnage selected AND loop field design. If the Ketchikan design temp drove the loop design then you may not have enough pipe in the ground.
Again based on the original load offered pipe should be adequate unless soil is dry sand (unlikely given the depth of excavation).
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Just a Mechanic;
Geothermal; Savings Underfoot |
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chadws
New Member
Posts:5
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| 21 May 2009 09:56 AM |
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Just to be clear the heat loss calc. is something I pursued on my own. I have no idea what my geo guy has but I'm pretty sure mine is now accurate.
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