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Old 03-05-16, 08:53 AM   #21
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Sam, +1 on Jeff & Steve's comments. I will add that the efficiency of an open source heat pump depends heavily on the energy needed for pumping. Your ground & groundwater temp is probably around 47F where you are (confirm on a map), and you will surely drag the temp down below 40F in your heating dominated climate. You will need to plan for at least 2gpm per ton of capacity.

If your water table is consistently less than 25ft down from your pump location, you can use a shallow well pump and the lift isn't too bad. If not, the energy required to pump 8 or more GPM from lower depths really adds up. You only need 2 boreholes, saving installation cost, but the average efficiency gets dragged way down by a pump powerful enough to meet peak flow requirements. If you were going to pump that much water anyway to fill a lake or somesuch then it doesn't matter much.

The beauty of a closed loop system is because it works like an elevator with a counterweight. The energy required to pump your fluid up the pipes is returned to you as it flows back down. The only "wasted" energy is the amount required to overcome flow resistance. If designed properly, that amount can be very low.

Concerning frost on ASHP coils: I really think it's mostly a nonissue now. The worst possible conditions would be near freezing when it's misty and 100% humidity outside. During these conditions I've never seen frost on the coils or moisture draining from the unit indicating there had been. Air can hold only 1/10th the moisture at 32F as it can at 95F.

I and others have talked a lot about raising the efficiency of heat pumps. Check my posts, especially starting HERE. The important thing is the amount of temperature "lift". If you don't have a high water table so water doesn't steal your heat away, you can have a perimeter of shallower boreholes around your home, using solar thermal collectors (dedicated or behind PV panels) to raise the soil temp under your home to 73F or so during the off season. 135F output from a water/water heat pump using a 73F source is more efficient than getting 105F water from a 40F source. You are now passively heating the home from below in winter but not continuing to heat when the house is above 73.

135F water is hot enough for retrofit hydronic heat with transfer plates (the warm floors I mentioned) as well as the ideal (and safe from Legionella) temps for DHW. Combining systems and using a buffer tank so you can size for average load instead of peak load could get you free of your energy companies.

I will never see -15F in Atlanta. Does anyone have experience with a modern inverter drive heat pump in those temps? Does it shut off below a certain temp as Sam's did, or does the output just dwindle down? At least the COP would always be greater than 1 and therefore better than resistive heating, since you get the energy consumption of the compressor and the indoor fan back, unlike cooling mode where you are trying to get rid of heat.

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Old 03-05-16, 09:03 AM   #22
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Jeff, those EER numbers are off a bit. 1:1 COP=3.41 EER, since 1 Kw=3412 btu. A COP of 4-5 would be to 13.6-17 EER. An EER of 30 would be a COP of 8.8. Doable, but very lofty. Were they getting SEERs of 25-30 instead?

Sam, if you are unfamiliar with any of the terms we are describing, shout out if you can't find your answer after searching.
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Old 03-05-16, 10:53 AM   #23
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In general, all of the manufacturers inflate their EER / SEER / HSPF ratings on banner ads, posters, line art, etc. Most likely, the advertised values are peak values, not hard ASHRAE or ARI test numbers over the range of operation. The easy-to-see numbers are inflated like wattage ratings of knockoff audio amplifiers and speakers! The main number-inflating factor in the geo heat pump testing is that the numbers are calculated without water pumping power in the equation. This is one big reason why the larger-capacity units nearly always beat the smaller units in the standardized tests, and why the numbers are better in heating mode vs cooling mode.

Let's say we are using a super duper waterfurnace 7 series, with a pump-and-dump borehole with 65 degF source water temperature (not totally unrealistic). At the high end of its capacity range, the COP is going to be around 5, and the unit is going to greatly exceed its BTU rating, maybe moving 140% of its rated heating capacity. As we slow down the compressor to reach rated capacity, the COP might soar to above 7 at its rated capacity, maybe even reaching 8 at normal water pump speeds. If we then run the water pumps at full throttle, the instantaneous peak COP will rise even higher (near 10-11), then fall off as the balance point is reached. Believe me, the marketing teams will encourage the engineers to push the envelope as far as they can to inflate performance numbers.

Of course, those with a good grasp at the factors at play inside the box and elsewhere in the system are going to voice skepticism when presented these numbers. For those potential customers, most sales pros have no problem producing spreadsheets common to the HVAC industry which present a more realistic picture of actual field performance. But there is a major tendency in the entire residential realm for the manufacturers to quote inflated values on big ads. Some of the less reputable companies don't provide enough test data to establish a level comparison, making it incredibly difficult or impossible to do so objectively.

My main point here is there are so many configurations and factors to consider, that you really have to ask the right questions and look at a number of measurements to get an apples-to-apples comparison between units. Many GSHP units don't even have water pumps or fans inside the box, so presenting the total system performance questions has to be narrowed down from the getgo. The governing bodies have decided not to do this narrowing down, giving the manufacturers extra leeway during the certification process.

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Old 03-05-16, 11:51 AM   #24
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Even if there are pumps in the box, their energy draw is not subtracted from the COP, making those advertised numbers bigger.

From Wikipedia: "ASHRAE transitioned to ISO 13256-1 in 2001, which replaces ARI 320, 325 and 330. The new ISO standard produces slightly higher ratings because it no longer budgets any electricity for water pumps."

Rough example: At 600w per ton of capacity for the compressor power alone (should be this or less), 4 tons is 2400w. If we lose maybe 40 feet of head pumping 10gpm through the heat exchanger, 50' each way of 1" piping to the loop field, and the loop piping, plus lift the water 100ft (open system) the pump will take about 350w, assuming 90% motor efficiency and 78% pump efficiency. That drops our "rated" efficiency almost 15%. Since the heat pump efficiency will go up and the water pump efficiency will go down at lower loadings, the actual efficiency will be affected by the pump draw by a much larger percentage at lower loadings.
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Old 03-05-16, 05:08 PM   #25
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Quote:
Originally Posted by samerickson89 View Post
Okay I'll definitely be taking a look at those when I get a chance! Luckily cooling isn't a huge concern due to the shape of the house (cracking open a few windows at ground level and up in the cupola is usually enough to keep me cool), so I should be able to wait until summer when school's out. I'll definitely make sealing up the doors and windows before next fall a priority though.

From what you said about heat pumps, it sounds like mine is the conventional type. As it got colder this winter, it actually started to sound worse and worse when it was running. Then when it got well below zero, it just quit on me. When I called tech support and gave them the error code it was displaying, they said it's a compressor issue and that their units aren't designed to operate below ~15F. Would the inverter drive type be able to keep up when it gets that cold? And would it still draw a lot of power in the cold months (compared to ground source, not to my current system)?
This sounds like a good approach to me. In the beginning of your quest,try to get as much historical data as possible from the utility companies, maybe even the previous owner. While you're at the utility office, inquire if they do free or cheap energy audits or weatherproofing services. If so, jump on the opportunity and be there when it is being performed. Be polite, offer the techs or engineer drinks and such, and watch and learn. Take a little glimpse into what these guys do without becoming a pest.

Most likely, you will have to wait awhile for a report to be filed or an analysis to be prepared. Since your heat pump system is on the fritz, you may be able to get a few HVAC contractors to come out and do some bids on a replacement or complete overhaul. Again, stating that you might DIY some or all of the work is a bad idea for an accurate assessment. These firms are interested in doing everything for you. Let them do their preliminary work, and be there if you can.

Once the reports, analyses, bids, proposals, and the like are delivered to you, it will be much easier to determine where the home stands in multiple areas of interest. Since you are considering multiple strategies in both reducing your energy usage and generating your own heat and electricity, these papers will provide different points of view taking aim at the same (or similar) goal. You can then use your own judgement to weigh these options against each other. Being better informed before you do anything major will help prevent costly mistakes.

I would take the info you got from phone support with a couple grains of salt concerning your ductless system. Many of these units fault out with the same types of error codes when things go wrong. Just as calling the computer help desk most always ends up with your system needing a new motherboard or hard drive, the mini-split manufacturers blame the compressor or control board in nearly all cases where the system doesn't have a leak.

Read through some past topics, as many fellow ecorenovators have been the same place you stand now. This forum has become a huge resource because of people in all walks of life helping each other out. It is not that difficult to save a few thousand dollars a month in labor during the planning and construction phases if you have the time, determination and skills to DIY. Having willing friends or kids who will work for ice cream, pizza and beer doesn't hurt either!
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Old 03-06-16, 08:04 PM   #26
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"...fire retardant spray can foam (behind the electrical boxes) could save almost that much per month."

I've looked into this, spray foams such as Great Stuff Fireblock are not UL rated for this use. With enough heat or direct flame, they do burn. I tried this with a lighter, I have lit this stuff and it does not immediately extinguish when the lighter(not blow torch) was removed. Fire blocking spray foams are fire blocking in the sense that they prevent a cavity from having access to air, which will suffocate most fires. Electrical fires are different than this, they continue to produce heat in the absence of a fuel, this makes such a product as "Fireblock foam" unsuitable for this application and the product is likely to burn.

UL1479 fire rated sealant exists for this purpose as specifically labelled caulking products.
Here is an example of such a product:
3M 10.1 fl. oz. Fire-Barrier Sealant Caulk-CP-25WB+ - The Home Depot
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Old 08-03-17, 08:48 AM   #27
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I am a small flooring services contractor serving the Atlanta area. I am here because I think I will find a lot of useful information and this will help me grow my business, be a good manager and require helpful skills.

Thanks for accepting me here. If there is something I could help you out please don't hesitate to contact me

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