Energy consumption higher than indicated
Last Post 13 Sep 2014 02:32 PM by docjenser. 32 Replies.
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Estrogen HostageUser is Offline
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03 Sep 2014 01:00 PM
First question is whether the building and hvac system was properly commissioned? AC yes, house no.
Do you know infiltration rates (blower door results) duct leakage rates? No Do you have duct work in un conditioned space? No. What are your expected plug loads based on appliances and other stuff? No, although we didn't add appliances when we moved and our previous residence had a baseline consumption of about 500KWH for lighting and plug loads. I am attaching our power bills. I have some benchmarking notes on them.

Attachment: img-903115802-0001.pdf
Attachment: img-903115755-0001.pdf

jonrUser is Offline
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03 Sep 2014 08:23 PM
You might want to meter your hvac power usage separately with a kwh meter. Preferably one that could also be moved to other circuits for week long measurements.


Estrogen HostageUser is Offline
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04 Sep 2014 09:00 AM
I would love to do that. All the products I've seen that do that are quite expensive. Can you recommend one?


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04 Sep 2014 11:25 AM
Posted By Estrogen Hostage on 04 Sep 2014 09:00 AM
I would love to do that. All the products I've seen that do that are quite expensive. Can you recommend one?
You can buy used/surplus tested mechanical watt-hour meters for about $20-30 (or even new ones for under $50, now that they're going out of style in the age of "smart meters".)  

Low-end meter boxes/sockets at big box store home centers start at about $35.



jonrUser is Offline
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04 Sep 2014 11:30 AM
A search for "AC 100A Digital LED power meter Voltage KWh time watt Voltmeter Ammeter With CT" on ebay should result in a $12 device. I haven't used it, but it should work fine.


Eric AndersonUser is Offline
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04 Sep 2014 04:20 PM
Here is an article from green building advisor that you should read. It speaks to the need for residential commissioning. http://www.greenbuildingadvisor.com/blogs/dept/musings/residential-commissioning Since you are on track to spend ~ 6000$ per year in utility costs, it is well worth your while to correct what you can. Did the 500 kwh/month baseload include Hot water (DHW)? As far as the shell goes, IF you have a PDF of the house design, it would help in understanding the issues as well as how the house is oriented on the lot. If you have an iphone, use the digital compass feature and place the end of it flat against a window and write down the azimuth and indicate which side of the house that is. You indicated that the house has open cell spay foam. Is the wall framing 2x6? And is it 24” OC or 16” OC Do you have a bonus room over a garage? I would note that my suggestions do not directly relate to the geothermal system, which may be a large part of the problem. Some of the geo installers on this forum can get you on the right track there. Personally I think that you need to nail down all the shell details and an accurate manual J heat loss calculation, before you can tell whether the geo system is performing well. I think one of the things I would want to do is either submeter the geo system, or better yet add a sophisticated logging device like the TED. I am not making light of the costs involved, you just mortgaged up for a new house and now you are faced with this. No fun. Cheers, Eric


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docjenserUser is Offline
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04 Sep 2014 05:17 PM
Your geo-link report is fishy, it appears that the numbers are inflated, might be an error feeding the right data. What are your pump model numbers, and manufacturer? If you have 6 loops for 8 tons, and then a 1.25" header pipe coming in the house, this is very high pressure drop (flow resistance) and a very inefficient design for the loop field. Never mind that your pumps run all the time when 1 heatpump engages in 1st stage, which is very inefficient as well.


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arkie6User is Offline
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04 Sep 2014 07:42 PM
Posted By Estrogen Hostage on 02 Sep 2014 06:28 PM 
... Insulation is 5.5" of open cell insulation...


Is that for the walls, ceilings, or both?  If that is the amount and type of insulation in the ceiling, that is only ~R20 which is approximately half of the code minimum insulation value just about anywhere in the country.  And that ~R20 is not counting thermal bridging of the wood structure which would lower the overall R value even more.  If you have 2x6 ceiling joists on 16" centers, then your are looking at only ~R17 overall R value for the ceiling.


Dana1User is Offline
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05 Sep 2014 02:34 PM
arkie6 has a valid point. Kansas City MO is US climate zone 4A.  With 5.5" of ocSPF you'd have about R20, which meets IRC 2012 code min for walls, but is well shy of the R49 specified for attics/roofs.

MO state wide building codes regarding insulation is currently based on the 2009 IECC, which specifies R38 minimum for attics/roofs on zone-4. Assuming you have fully 6" in the attic you're probably looking at R22.

Just from an up-front cost point of view it probably would have been cost effective to to with smaller geo and higher-than-code-min performance on the building envelope, let alone a sub-code building. A 90 KBTU/hr heating load for a 4500' house is 20 BTU/ft2, which is about 2x the typical heat load ratio of a code min house half that size, and significantly higher than the heat load of my way sub-code 1920s antique, which comes in under 15 BTU/ft2.   Bigger houses usually have even lower BTU/ftratios.

Some building envelope issues can be cost-effectively rectified as a retrofit, but many are not.  But getting the geo to work properly would be the first priority, if that's really the root of it. The cooling load from the roof can sometimes be disproportionatly high when you have only ~R20 up there, and it may be worth treating that to more insulation sooner than later, provided it's possible without gutting the ceilings or something.

If the system has any ducts/air handlers outside of the insulation, that too can be an issue increasing load, decreasing system efficiency.


Bill NeukranzUser is Offline
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06 Sep 2014 01:44 PM
Posted By docjenser on 04 Sep 2014 05:17 PM
... If you have 6 loops for 8 tons, and then a 1.25" header pipe coming in the house, this is very high pressure drop (flow resistance) and a very inefficient design for the loop field. ...

Amen.

I too have an 8 ton vertical borehole field (in Dallas climate that's 8 boreholes, each 300' deep, with 1" HDPE pipe down and back in each).

I have 2" header pipe from the borehole field to almost to the equipment.

Best regards,

Bill


Energy reduction & monitoring</br>
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Estrogen HostageUser is Offline
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07 Sep 2014 06:32 PM
I'm working on some drawings, but I have to redact them a little before I'll post. House is a 2 story colonial with a wrap around porch and finished attic. 2200 square feet first floor, 2200 square feet unfinished basement, 1500 square feet second floor, and 1000 square feet attic.

It is definitely 1.25" PIPE from the pumps. 82 degree EWT, 89 LWT while in stage 1. I have six line trenches, three trenches. I think that is 9 loops of .75" pipe with a 1.25" manifold. You guys are probably right about the pipe size because it's noisy. I shut the geothermal over the weekend, to create a control. Weekends are always my highest consumption times, I used 58KWh yesterday, down from 125 the weekend before and 157 the weekend before that, and I had 5-6 hours of run time yesterday to factor in. I'll know what I used today tomorrow morning without any run time and an occupied house.


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10 Sep 2014 09:11 AM
"Design day heat loss was 72k BTU cooling and 90k BTU heating. "
Yet your installer suggested your loss was 119570 and gain was 79164. They also have an average balance point of 4-5 while your design temp is 6F. The good news about the loops is that the header size would only matter if the demand were truly as high as they said.

Do you really set the heat at 74F in the winter? that's what they designed for (oh and 74 in the summer). This has all the earmarks of an unevolved installer. The load is inflated and then the design is for nearly 100% of the imaginary load on top of which 4 pumps run continuously (though you likely need 2 tops).

The combination of inflated load plus a heavy (more heat pump than you'd need even if the load is accurate) design is what we refer to as "grossly oversized" which means you will pay too much if system runs as designed. You commented that all the companies suggested about the same size, yet all were different and the smallest was 75% the size of the one you purchased.

The good news is this: if your thermostats are programmed to respond by temperature drop (not time) you will likely use second stage as your auxiliary and with only 2 pumps (wired to run only when heat pumps are on) you will have a reasonably efficient system.




Joe Hardin
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docjenserUser is Offline
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13 Sep 2014 02:32 PM
Do you have the model number of the circulation pumps...???


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