Technical Help needed on GSHP and KW/HR use

[mbcijim]

I have two units in my brand new home, the Model 26 & 64. They are ground source heat pump units from climate master. I'm trying to figure out how many kw/hr they are using. Can someone help me? My home is using anywhere from 120-270 KW/day! Somethings wrong somewhere. I'm not smart enough to understand what this chart says. I'm hoping someone here does.

The units have electric resistance heaters built into them, I think they are the problem. However, I'm still trying to figure out my base usage, without the resistance heaters. The resistance heat on the 26 NEVER runs. But sometimes it runs alot on the 64.

Are you guys seeing a picture or a link? For some reason I'm getting the link. I have

after.

 

[Jerry_NJ]

mbciljim, just checking in to get connected to this thread. I think I've given most of what I have on this subject on the other thread.

Another point, my heating contractor who installed my GSHP did a "factory" study of my hours and gave me a print out of the heat loads/needs of my house given winter time 70 degree inside. The computer study used long term weather information to forecast the number of "degree days" at each of a series of temperatures from 100 degrees to 0 degrees. So, I know what my engineered heat load is when the outside temp is given, say 20 degrees, and it tracks well with the performance. Some data like that would help you decide if the hp is working properly.

Another test is to measure the temperature in and out of the heat exchanger. You also need to know the air flow in feet per minute (one has to assume it is as per the specification on the blower set-up, mine runs 700 cfm in recirculate, 1000 cmf in stage I and 1400 cfm in stage II), this has to be measured when the resistive heat is off.

How old is your installation, still under some warranty coverage? If under warranty I'd have the contractor out to explain why the resistive heat is coming on ...i.e., the high electric usage you are supposed to not have due to your investment in the gshp.

 

[Redox]

It is going to be hard to figure this one out unless you can get an hour meter on the compressors. It is possible to suck down 140 KWH a day with a 5 ton compressor, but it would have to be running 24 hours and not keeping up to do that. Try disconnecting the electric resistance heat and see what happens. Measure the temperature rise of the heat pump while you are at it. Since this is a new installation, I would venture to guess something is wired wrong or your thermostat is being overly aggressive. IIRC, you house is about 3500 sqft and has 7 tons of unit. This works out to about 500 ft/ton which is reasonable. I wouldn't expect ANY resistance heat unless it gets very cold or the compressor shuts down.

Chris

 

[mbcijim]

It is under warranty so I have been talking with my HVAC contractor. I owe him lots of money too, so he will take care of it.
How do I get a meter on the compressors? Is that something my HVAC contractor can do? I do have a kill-o-watt thing but that only works on 120V.
How do I measure the temperature of my heat pump, at the registers?

I used 130KW over the last 24 hours. I am assuming that my background load is around 20-30KW a day. Just two people, all florescent lights, one and half fridges, and an electric hot water heater with a desuperheater hooked up. So my assumption is my two units are using 100 KW an average day. I know that 30KW a day is probably low, but that was my historical use in the old house in the winter time. This house is more efficient, not less.

The electric heat is hardly kicking in any more. I had the thermostat set with setbacks when the house was unoccupied. I did knock 30-40KW a day off by eliminating the setbacks. I learned that heat pumps work better steady, they are not designed for even small (5 degree F) temperature drops inside the house (for anyone reading this considering getting one). No one told me that and I didn't read it anywhere. Better off holding the temperature steady.

 

[Jerry_NJ]

Surprised that the contractor didn't advise you to keep the setting constant, mine even recommended putting it in full automatic where it would switch between A/C and Heat automatically. Say set the A/C for 75 degrees and the heat for 70 degrees, that way they can't get into an argument. He also recommended leaving the blower on low speed 24/7.

I followed none of the recommendations, and as I may have said earlier, I watch the thermostat when warming up to be sure the Aux doesn't come on. That means I'm raising the temperature setting by 1 or 2 degrees at a set. It seems there's a time-out such that when it is really cold out, say 50+ degrees below what the house is set for, my heat loss is so close to the full stage II HP output that the Aux will cut in for short periods , say 5 minutes to 10 minutes, to help the HP along with only a 2 degree deficiency - demand (unsatisfied in some delta time). I did disconnect the second Aux, so my maximum Auxi resistive heat is 5 KW, or about 17K BTU, and as my stage II is putting out about twice that much at a COP of 3+, I'm still getting an average COP of 2 with the Aux on, so still much better than a pure resistive system.

Of course this isn't a problem on A/C. There are no higher cost auxiliaries to speed up cooling, stage II is all there is.

 

[Redox]

Unpaid contractors do have a way of returning your calls. Keep him involved, but don't piss him off. He may decide final payment isn't worth it.

The easiest way to measure compressor run time is to put an hour meter on it, but you risk voiding the manufacturers warranty. Ask your contractor if he will put an hour meter on it for you. He might be willing to do this just to end the argument. The easiest way is to put a 24VAC hour meter on the contactor coil or a 240 VAC meter on the contactor itself. If he resists, you can put a current transformer on it which is noninvasive. Hour meters are available at Grainger, but I'm sure you can find them for less on E-bay. This will not give you KWH but multiply time by estimated KW and you should be in the ballpark. I haven't found an inexpensive K-A-W meter for 240VAC. The wattage on a GSHP should be pretty steady.

You just need an accurate thermometer that inserts in the duct to measure inlet and outlet temperature. The dial kind that cooks use are pretty accurate, but the electronic versions are pretty fast and cheap. See:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95382

No experience with this particular one, but that's what most mechanics use. An IR thermometer isn't any good as it is just reading duct temperature. Drill a 1/8" hole in the supply and return duct and probe away. Generally, I would expect to see a 15-20 degree rise, but a GSHP may have different numbers depending on loop temperature and flow rate. Same holds if you have a 2 speed compressor or variable speed blower. Anything in the 80-90 degree range or more is good.

130KWH seems like a lot considering the weather we're having at the moment. Our base load is about 20KWH with nothing major running, so that's a realistic number. 100KWH/24 hours is a little over 4kw continuous. A 5 ton unit running 24 hours would do it. Does it seem to be running all the time? I would expect it to be on only about 1/2 the time or so. It would be a PITA, but you could babysit the unit for an hour or so and write down the start and stop times, just to see if you are in the ballpark. Boring, I know, but easy to do.

Setback on a heat pump is a whole 'nother argument. I agree, keep a steady setpoint until you get this sorted out. There are setback stats made for heat pumps that use "intelligent recovery" to minimize backup heat. Since a heat pump is so slow to catch up, they don't really save you very much, IMHO.

Chris

 

[Jerry_NJ]

Chris,

Thanks for the link to HF on the digital stem thermometer. I'm an old B&W;Photo Dark Room Guy (guess the "old" part goes with the rest...remember film camera?) so I have a couple of try thermometers - but one of them isn't working well. They are the old spring analog type. I'll buy a new digital next time I order from HF. Their stuff is cheap, but some/most times good enough for what I need.

Speaking of power, I have measured my HP but volt/amps only. I have a total (compressor, pumps, blower) of 1.8 KVA for Stage I and 3.3 KVA for Stage II. My blower is 700/1000/1400 cfm for Stage0(off)/StageI/StageII. I assume that is close to the KW as well, but wonder what the power factor might be. These are all inductive loads.

I'd add, be sure to measure the air temperatures as close to the heat exchanger as you can, but far enough away to assure a good mix of the air flow. My heat exchanger is vertical and is followed by the cabinet chamber that has the squirrel cage blower. I measure the Up temperature above the blower (too close to the resistive heaters to get a good measure on them when they are running) about a foot up the vertical run. I measure the input air temperature just before the air filters were all the air mixed from all the rooms is combined.

I get about 18 degrees in Stage I at 1000 cfm, and a bit over 20 degrees in Stage II and 1400 cfm. The ratings are about 22KBTU and 33KBTU respectively for a loop temperature of 32 degrees. My loop seems always measures above 40 degrees as measured on the surface of the pipe under the pipe insulation sleeve.

In addition to this I estimate the HP is giving me about 50 gallons of hot water with a temperature rise of about 70 degrees over incoming 50+ degree well water. The hot water loop is rated at about 2.4KBTU, or about 700 watts resistive heating equivalent. So, it is slow going and if there is a big demand for hot water the tank has to be allowed to cut in its 5KW resistive heating too. I get by most days with only HP generated HW. Keep in mind the 700 watt equivalent going into the hot water is costing me about as much as 200 watt resistive would cost due to the 3.5 or so COP on the HP. My HP is rated to have a COP of 3.1 in Stage II and 4.3 in Stage I, and it runs in a mix of those speeds during cold weather, that's why I use the number 3.5 for the average COP. In any case, big time savings over resistive heated hot water.

Chris and I had a long discussion on how to modify my hot water tap to the HP. The mod I put in works great, and I found out after that that the method we arrived at is the same as the current factory recommendation....shows we have some good "engineering" on this forum. The factory recommendation that was in effect 15 ears ago when the unit was installed used a commont concentric tap connected to the drain hole. This could work, but no in any system with minerals in the water. I'm non a well, and don't consider the water "too" hard, but boy it sure was hard enough to stop up the tap in a few weeks.

Again, with (only) 2,000 sqft on two stories, well insulated, my consumption without the aid of my wood stove is estimated to be closer to 55KWH per day during the period December 10, January 10 when we had some real cold weather, single digits at night at least twice, below 0 once and a lot of low teens at night and 20s in the day. This was one of the coldest periods we've seen in this house over the past 20 years. That said, given you have almost twice the space, I'd estimate you should have averaged in the neighborhood of 100 KWH per day during the same period...I think that's about whe Chris estimated..no looking back :>)

 

[Jerry_NJ]

p.s.

I still believe in setting back the temperature, and if it were just me I'd completely disconnect the resistive auxiliary/emergency elements, then there would be no management necessary to bring the temp back up, just set it to the desired end-point...of course it may take all morning. I'd put on a jacket, but that doesn't fix my wife's needs. She's cold even when we're up to temp, 66 to 68 degrees.

 

[Redox]

I have no experience with that particular HF thermometer; I just posted it as an example of what you are looking for. At the price they are asking, I would buy a few of them and check their calibration in a cup of ice water or something to see how they do. The ones that are available to the trade are a lot more expensive and presumably more accurate, but HF has a track record of acceptable quality and good pricing. Use the same thermometer for inlet and outlet readings to minimize error. This is also a good example of where an IR thermometer is no good; you need an insertion thermometer to get a good read. It's also worth mentioning that you want to take the discharge temperature after an elbow or something as the IR energy coming off a heating element or heat exchanger will affect the thermometer. Infrared follows a line of sight pattern and will change the number, even if the HX isn't "glowing". Generally after an elbow and a few feet down the duct will be enough of a "shadow" for an accurate measurement.

I haven't found a 240 volt equivalent to the K-A-W meter or anything inexpensive that can read power factor. There is a meter available from E-mon that is accurate enough for billing purposes, but it is hard wired and probably not cheap. I see these used commercially for tenant submetering, but I have no idea how much they cost. It might be worth an e-mail to the company to find out.

http://www.emon.com/products_class1000.htm

I have use of a Fluke power analyzer that I have used to look at various loads around the house. It can't measure KWH without extra software but is very accurate at KW and PF. For the record, I have compared the K-A-W to the Fluke; they are very close to each other. I have two air-air heat pumps of the same age and size that have very different power factors. One is set up as a capacitor start and one is just PSC. IIRC, the PSC unit runs about a 0.6 PF and the CSIR one is more like 0.8 or thereabouts; way too different to make any guesses or generalizations. It is possible to back calculate the power if you know the temp of the water and air entering and leaving, but this is still just a guess. A true power meter is the only real way to know.

It sounds like you have done your homework, Jerry, and I'm glad the desuperheater is working out. In my mind, electric resistance is something to be avoided whenever possible! I didn't want to start the argument about thermostat setback on a heat pump, but if you are going to do it, you might want to put in an outdoor thermostat. They are common on air-air heat pumps because their performance varies with outdoor temperature and shouldn't be necessary on a GSHP, unless you are doing setback. They are wired in series with one or all of your electric strips and keep the resistance heat off unless it is very cold out. The emergency heat should bypass the OD stat in case the compressor quits and you really need heat. You can put up with slow recovery if you don't set back too far. "Intelligent recovery" can't predict your moods and desires, I've found. :roll:

Most GSHPs are sized to cover 100% of the heating needs at design temperatures with just the compressor, but this will vary with the climate and construction. The backup heat shouldn't ever be necessary but may be required by code to cover "emergency" use. Try disconnecting it for a while and see what happens. Many air handlers have the electric heat on a separate breaker and it may be possible to just open the breaker to shut it down without having to disconnect anything. If the heat pump alone can't keep up, there may be a problem with the system or design.

Chris

 

[Jerry_NJ]

The IR heat is what really got me going. I was measuring the heated air temp above the blower with the heat exchanger on the other side and at 90 degrees. There I'd get the stated +18 degrees at 1000 cfm. Then when I turned on the 5K resistive I expected to see another about 11 degrees, but I saw something closer to 20 degrees, which at first made me think my HP wasn't working up to specs. Then, I suspected the unexpected heat rise was because my darkroom thermometer was getting a lot of radiant heat from the resistive element that were no more than 12" below and likely wide open to the thermometer probe.


Something I got off the HVAC forum on "The Home Site" (Garden Web) is:
BTU = 1.08 x DeltaT x CFM
DeltaT = BTU / (1.08 x CFM)

Converting BTU/Hour to KW/Hour one gets

= 3414 / (1.08 x 1400)
= 2.26 degree rise per kw

thus for a 5KW resistive heat I should see +11.3 degrees.

This made me feel a lot better about the +22 degrees off of the heat pump. Right on for the spec of 33KBTU for my Stage II HP output. Lots of approximations here, of course, e.g., the 1400 cfm is the spec for the blower, I do not have a measurement of how much air is flowing.

 

[Corey]

270KW (h?) per day??? Shut down the grow op!! I’m trying to figure out how I use 30 KWh/day with two people!

Seriously, though if you want to track down power consumption on bigger stuff, you’re going to need an amp clamp. This could be something as simple as:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96308

Technically, it would be best to measure the voltage of your line as well, but for a rough estimate, you can assume 230V. If you can get to the main feed line for the house, that would be the place to measure. Measure the amps on both of the hot wires, then it’s just 230V x amps = watts. Divide by 1000 to get KW and compare that to what the meter is reading.

If you can’t get to the main line, Then you’d just need to find a point where the individual component line is separated into the component wires…should be black, red, white, possibly copper and/or green. The black and red wires are what you’re looking at. Separate them and measure individually – they should be equal, but never hurts to check. Then run through the same math.

I would think you might also be able to contact the utility company and have them take a look at the meter, they should have the pro equipment and be able to tell you if it's working correctly.

 

[Jerry_NJ]

Indeed, that's the approach I"ve taken, being the proud owner of a clamp on from back in the days when all were analog and very expensive. That's before HF was in existence..well long before China was in the world market.

I opened my CktBkr panel and clamped on to each, the compressor, the ground loop pumps and the blower... and computed Volt Amps, that's all I/we can do when using the amperage without knowing the phase relationship to the voltage. But, if the power factor is near "1" they are one and the same. I'm sure the power factor is less than one, and if even 10% less it is a difference I'd like to know.

Here's another item I got off of The Home Site, on Goodman (a brand I recognize but don't think of as the top-line product).
(broken link removed to http://www.goodmanmfg.com/Portals/0/pdf/SS-SSZ14.pdf)

It shows the air-to-air with a COP of 2.5 at 15 degrees, almost makes one wonder why most of us would buy a geothermal...here in central NJ 15 degrees is near the average low...does go below zeros once or twice in five years. The Goodman also shows a COP of 1.9 at ZERO degrees. Does that include the cost of defrost, or is the the COP when the unit has no frost?

I wonder if the a-t-a HPs have gotten that much in recent years. My original a-t-a was down to about "1" at 30 degrees, a common temperature her in NJ during the winter. That's why I went geothermal 15 years ago.

 

[woodgeek]

Not to get OT, Jerry, but I'm running one of those Goodman's down the road from you. Installed a 4 ton SSZ14 last summer, ~$3k more than a conventional central air system. I looked at the same table and figured that air-source looked pretty favorable relative to my oil heat. So far, measured outlet air temps, total BTUs and electrical usage have tracked the nominal heating data table to within error. In fact, when the outdoor RH is high, the output rises measurably (outdoor coil runs at dew point>air temp). Looks to offset 500 gals oil using ~$650 of elec.

Only unknown is durability. Goodman rates for cold usage, but I shut 'er down below 15 degrees and during heavy icing conditions (<10 days per season). I guess I'll find out eventually....

 

[Jerry_NJ]

Woodgeek, (a wood worker I assume),

I don't have any knowledge about Goodman other than my neighbor replaced one of his two central A/C units with a Goodman, and while exchanging on another HVAC forum a guy with a Goodman HP put in some good stuff, including the equations I showed above, and some comments about his Goodman HP. I was surprised by two things, the heat rise across the exchanger and the cold weather performance, per specs. My 4 ton geothermal (Waterfurnace) is that only in A/C, in heating its maximum is 33,000 BTU (really a 3 ton heating), but it will give that using about 3KWatts (no defrost needed) when the outside is at zero, or colder which I did see a couple of weeks ago.

I don't understand the "runs at dew point>air temp". Seems you are saying the HP gives higher heat output when the dew point is higher than the air temp, or when condensation is forming on a surface at the air temperature. That would seem to me to cause more icing on the cold hp coils taking heat out of the air, i.e., need more defrosting. Perhaps I don't understand what causes a air-to-air hp to require defrosting. Hum, when in defrost I understand the resistive aux heaters are turned on so that the exterior coils can be heated by running the HP in A/C mode for a short time. This could, I suppose, cause the inside temperature to rise.

 

[mbcijim]

Thanks guys. I'll need to spend a bunch of time on this. Your answers got a tad bit technical. I like it, but I have to educate myself on this new field of mine...

 

[Redox]

This is why heat pumps can be so mystical; it's hard to see how you can suck heat out of cold outdoor air or a ground loop and have it heat your house with a refrigerant and be efficient, all at the same time. Just don't neglect the Summit, Jim! Wood heat is just so much nicer and probably easier to understand.

Since the thread is now officially off track, we can take this even further. Air-air heat pumps have come a long way since the mid 70's when they were first introduced. A lot has been learned in that time and they just keep getting better. It isn't your imagination that they work better in cold weather than they used to. Back then, we used to shut them down below about 0 degrees or so as they actually became less efficient than electric resistance, not to mention the difficulty in restarting a cold compressor. Nowadays, the better units are using scroll compressors that have a measurable advantage in volumetric efficiency over a reciprocating compressor, especially at low temperatures. Just as we can appreciate what the EPA has done for wood stoves, the same has happened in the HVAC world. Currently, the minimum SEER rating is 13 and this has forced manufacturers to push for greater efficiency. Scroll compressors, ECM fan motors, demand defrost and better coil designs are the biggest improvements. Variable displacement or multi speed compressors are becoming more mainstream and all these developments are getting thoroughly field tested and improved on. Sometimes the EPA is a good thing!

When you get right down to it, there are only about 4 manufacturers of compressors used in the US market and the Copeland scroll has the lion's share of that market. It has the longest track record and the largest installed base of any manufacturer. Carlyle (Carrier) tried to build their own a few years back and didn't have much success. They eventually started using the Copeland with good results, but this must have hurt their corporate pride to outsource a compressor. I think they have since bought the rights to another scroll (Bristol?) and are back in the scroll business. Bristol (York) makes a very good reciprocating compressor that is raising the bar for all the other manufacturers. I have seen Bristols live through conditions that would have wiped out a Tecumseh or lesser compressor. Trane also makes a very good recip (Climatuff), but their scrolls are mediocre at best. I'm not sure they are using them in residential units any more. All of them are better than what was produced back in the 70's.

The same thing holds for parts like the fan motors and controls. GE makes ALL the ECM fan motors in the US and there are (or were) only 2 manufacturers of reversing valves. When you get right down to it, all Goodman is making is the cabinet, nameplate and maybe the coils, though many outsource the coil production. "Under the hood" they are all pretty much the same. Goodman used to be Janitrol and was never very well regarded, but they have come a long way over the years. They don't have the marketing that Trane does, but who wants to pay for advertising? What Goodman does is sell through a network of smaller independent contractors who can do every bit as good a job as the big guys and often better. Most of them are staking their reputation on your system and have more of an incentive to make sure it works well and that you are happy. Little details like duct sizing make more of a difference than then name on the side of the unit.

Now for the technical stuff: Jerry, you do know the CFM! Measure the current and voltage of the heater and the temperature rise as accurately as you can and solve for CFM. This is one of the most accurate ways to measure airflow and would hold up to scrutiny by any engineer. The PF of an electric heater is 1 and 1 watt = 3.412141633 BTU by definition (in round numbers). The accuracy of your instruments is the biggest error. Altitude and humidity have some effect, but can be disregarded for the most part.

Air-air heat pumps can extract some latent heat (humidity) from outdoors, but this usually results in frost that slows down heat transfer. If the unit always ran at 47F (design point), there would never be any frost and a humid environment would be a good thing. Condensing furnaces take advantage of this latent energy by condensing the moisture out of the flue gasses. Since there's no creosote in a gas burner, they can get away with it. The problems occur around 35F and high humidity conditions; your HP is going to look like a snowball after a couple hours. All this has to be periodically thawed out and all that latent energy goes right back into the puddle of water under your heat pump. Most units will turn on the backup heat to maintain comfort, but you can disconnect it if you want. I actually never got around to installing the electric strips on our upstairs heat pump and nobody is complaining. It does get a little drafty at times, but the unit still keeps up, even in single digit weather.

"Demand defrost" uses various sensors and electronics to determine the best time to defrost the unit. This was tried years ago and fell out of favor because it couldn't take into account every situation and climate. When it screwed up, it resulted in an expensive service call, usually to manually defrost the unit and replace a few unnecessary parts. Manufacturers almost universally reverted to a time-temperature based system as it was simpler and more reliable. These systems put the unit through a defrost cycle every 30-90 minutes whether it needed it or not. At very low dewpoints, there would be little frost, but the unit would defrost anyway; not very efficient. Now that the EPA is forcing the issue, manufacturers are trying to milk every last BTU out of your KW and forcing them to rethink what was acceptable years ago. The result is a new interest in demand defrost. Most are using electronics to measure delta T or delta P across the coil and calculating the best time for defrost. This is more efficient and actually cheaper to install than the defrost timers of years past. The difference is like fuel injection vs. a carburetor. Let's all bow down to the gods of solid state!

continued on next page...

 

[Redox]

See! Software cut me off.

GSHP users don't have to worry about defrost, but other problems can occur. What happens if you develop a leak in that underground loop? It's rare, but it does happen. What about the heat transfer fluid? Water chemistry being what it is, it would probably be a good idea to send out a sample to a lab now and again to set it analyzed. What if you are using glycol or (shudder) methanol and it gets out into the ground water? I haven't heard of it happening yet, but the possibility exists. What about PERMAFROST? I have heard anecdotal evidence from contractors installing large GSHP systems that they are having to space out the wells over a wider area. If you are constantly sucking more heat out of the ground in the winter than you are putting back in the summer, you could run into a problem over time. Admittedly, this is unlikely with a single well installed in the middle of nowhere, but what about an entire housing development? Nobody knows; this is all new stuff. The industry is still in its infancy and the problems are still being worked out. The technology is mature enough that I think it would be a good investment if I were going to stay in the house for a while, but my house is sited on an old quarry and the chance that I could drill a well here are very slim. I don't even think I have a straight shot at a sewer line. I'll be sticking with my air-air units for a little while longer. Besides, I'm still holding out for a gasifier.

Sorry if I can be long winded; hope it wasn't boring. And Corey; grow ops should be SOLAR! :coolsmirk:

Chris

 

[woodgeek]

Redox explained it all better than I could....

After using a run of the mill, current vintage air-source HP, I am convinced that the payback of a GSHP relative to an air-source is going to start taking longer and longer in most applications and climates in the lower 48. Unless elec gets a lot more $$ than it is currently, I think air source HPs are going to slowly chase the geos to the canadian border (for new installations).

When I was figuring out what to do about my potentially $4k/yr oil bill last summer in my 'no gas option' house I was thinking geo, and worried about financing the install, or getting some 'bleeding edge' tech, cold-climate heat pump that I was worried was untested (low volume) vapor-ware that shows up on 'green' websites. After looking around, I found that the bottom of the line, standard air-source HP used all over (Goodman) looked on paper like it could handle my application. A lot of folks on the 'net dis the Goodman's, but as I read more, the picture Redox painted became clear--the core hardware units are much the same under the hood, Goodman has got its build quality up (as its sales volume became very large), and it all comes down to proper installation--I watched that poor HVAC guy like a hawk.

Since I wanted CAC and needed to install ducting anyway, it was a low activation ($$) barrier to get the HP. My neighbors with the same house had CAC with small high velocity ducting put in for ~$2k less than my install. The small ducting is not forward compatible with a HP if they just want to replace their compressor in the future....and the company that installed their CAC is also their oil distributor. Hmmmm.

Let's talk frost--I couldn't get good info online, so I've had to experiment. The Goodmans have 'primitive' defrost that just does a defrost cycle every 30, 60 or 120 minutes of run time, whenever the outdoor coil temp is below 40F. Sounds like a big waste, right? The more I think about it the less I worry. Although it sounds like a timer is non-adaptive, the system actually IS adaptive, as the defrost cycle runs until the coil temp gets above ~40F. IF there is no frost, that takes like 2-3 minutes, given the low thermal mass of the coil itself, and then its done, maybe ~2,000 BTUs, and just a couple cents of elec on my aux every 60 minute cycle. While the defrost takes longer when needed (maybe 7-8 minutes during snow or sleet), those conditions are a small fraction of total time. I find typical defrosts at 25F for dry conditions are still only ~4 minutes/hr. Think of it this way--if the outdoor coil is big enough (and the BTU has dropped off) then the coil can bottom out above the dew point during dry weather and have minimal frosting. In the end, I think I average ~15-20kWh/day for defrost. Definitely a significant cost of the air-source, but not worth losing sleep over.

In the end, I rationalized getting the cheapest air-source HP I could (given that it specs to cover >80% of my heating demand). As with computers, I think the technology, efficiency and value of these HPs are rapidly maturing so it doesn't make sense to get a top of the line ($$) compressor. It makes more sense to get one that will do the job now, and just replace it when the tech gets better in a few years (or 10), rather than trying to get a tank and keep it going for 25 years.

Sorry about the dew-point confusion. I was simply trying to say that I have completely validated the data in that table in my own 'field' trials. The only deviations have been during high RH, when the output and elec usage both increase, b/c the coil is running a little below the dew point, rather than 20F below ambient air temp. For dewpoints above freezing, the system runs less often at higher BTU/hr and similar COP. For dewpoints below freezing, the defrosting goes up, but I think the total system BTU/hr is still comparable to dry conditions b/c of higher output between defrost cycles (assuming it doesn't get choked off).

cheers,

geek (science-type, not woodworker or eater of weird objects)

 

[Jerry_NJ]

Chris, Woodgeek:

Great inputs, I think I'll copy the last two posts and save them, or is there a "copy right"?? :>)

The defrost strategy on the Goodman sounds reasonable to me and isn't just a dumb defrost every delta-T, well it does, but seems it watches and if the defrost is light, or not needed the unit minimizes the "loss". I do understand you to say your measurements seem to suggest the COP does take into account the defrost, or that the defrost is such a small cost that you can't "see" it.

Well, I already have a geothermal and no leaks so far, I also have 5+ acres, so the only nearby vertical loop is mine. I'd say the two 250' deep loops are no more than 10' apart (going from memory, I may have written it down somewhere in my records...in case a dig becomes necessary), but as we have a solid water table at 100' an (my well) and most likely water at about 15' there is very good heat transfer in the loops.

With heating oil down to around $2 this winter it is hard to beat the cost of oil heat with electricity at about 17 cents per KWH here in NJ. Still, I know my HP saved at least $2K last year over oil, when oil was near $4 per gallon. I didn't burn much wood last year either, this year I'll burn about two cords which means a lot less electricity this year.

 

[woodgeek]

Jerry,

I'm pretty sure the Goodman Heating table does NOT include any defrost elec demand. After all, as Chris says, you can leave the aux off and suck (cheap) heat out of your house for a few minutes for defrost, and then make it up later. I suspect during light frost conditions you wouldn't even notice. I have it wired to run a 10kW strip on defrost just so I don't give the family a chill from time to time, which is worth it for me. I think I need about 7500 kWh/season for the compressor and blower, maybe 1500 kWh for the defrost, and 100 gallons oil for backup (wired in instead of elec backup). I guess that means defrost pulls my seasonally averaged COP down by 15-20%, I figure SCOP ~ 2.3-2.5 or so.

My costs are different on this side of the river: my oil costs $3.19/gal, and I can get windpower for $0.10/kwh from PECO (with a winter heating discount). This season I'm saving ~$900 and ~6 tons CO2 relative to oil by using windpower.

 

[Jerry_NJ]

Woodgeek,

Thanks for the estimates, and nice "green power" at a lower cost. I understood most such electric was at a premium price. We're paying about 17 cents and it is about half nuclear and half coal. So, oil should have nothing to due with the cost, but oil sets the market price for energy...could that be "wind fall" profit (I don't mean windpower) for JCP&L Sounds like it to me.

My engineered heating load (average year) is about 60 million BTUs. If I get an average COP of 3.5 (optimistic) that's ](60,000,0000/3.5]/3.4 = 5,000 KWH. I have an "all electric" 1985 built 2000 sqft two story. Has the double garage on the North side to help reduce energy use. Hum, that's $850 at 17 cents a KWH and includes much of our hot water too. If I assume 100KBTU per gallon of oil, that would be 600 gallons, and at least $1,200 but as much as $1,900 at your quoted price per gallon. A nice savings at either. But, my depreciation cost on my system is at least $400 per year higher than an oil furnace. So my savings are minimal at $2.00 per gallon if one can get heating oil for that price, I really don't know what the going price is.

 

[mbcijim]

Update: I had the HVAC installation company out to my house. They tell me nothing is wrong, system is fully operational, it is running the way it is designed.

We re-wired the backup resistance heat so that I have to manually turn it on. Yesterday was about as cold as it gets in my part of Pennsylvania. High of about 20, low of 7 or 8. The thermostat is set at 70 (permanently with no setbacks), at one point it did get down to 68. When I got up in the morning it was 70 in the house. I used 110 KW in 24 hours. Previously on the coldest days I had used as many as 270 KW. Yesterday the resistance heat never turned on.

The house is 3,500 sft with two rooms with 18' ceilings. I am assuming my background load is around 30 KW/day. So my two geothermal units are using 80 KW on the coldest days. So worst case scenario is 80 KW x 30 days = 2,400 KW @ $.10/KW to heat is about $240/month to heat my home in the coldest month. Was it worth the investment of geothermal??? That remains to be seen. There is some satisfaction in knowing I'm not sending over $2,000 a year to Iran.

I'll know for certain in a month whether my changes worked, but overall, this seems very good. Plus I now have 2.5 cords split and stacked, with another 5 waiting to be split to get ready for the Pacific Summit for next winter.

 

[Jerry_NJ]

Sound like you've got it, and your usage seems reasonable for the size house you have. You "gota" love that 10 cents per KWH, that's great and green too, priceless.

I run my Quadrafire Insert as much as I can on real cold times, but do let it die back overnight. My Geo HP picks up the load sometime during the night.

Good luck with the work splitting and stacking the firewood, hope it seasons well. If you burn a even a couple of cords of seasoned hard wood during the coldest periods you'll see a good reduction in electric usage. But, unless you get your wood for cheap to free and count your labor as exercise, you'll not save a lot over geo hp electric at the 10 cent rate.

I harvest some wood but buy 1 to 2 cords a year at about $200 per cord...that puts the wood cost for the purchased wood about equal to my geo hp heating cost. I am paying 17 cents per KWH right now. If you can send/post contact information on the lower cost green electricity I'd like to check into it myself. I must be within 100 miles of your location here in north-central NJ... Clinton Township, about 50 miles NE of Philadelphia.

 

[Redox]

I can burn that much electricity in the summer with the a/c on and heat generally costs more than a/c. FWIW, I'm hearing of people with smaller homes that are hitting $400/month on NG in these parts. If you can hold 70F indoors at design conditions outdoors with just a compressor, you are doing good and there is nothing wrong with the heat pump. It sounds like it is sized appropriately and working correctly to me.

Now that you've proven that you don't really need resistance heat, you might want to consider a more sophisticated control system for it than a manual lockout, especially if you are away for long periods of time. If you wired up a simple thermostat set at 60 degrees or so, your pipes won't freeze if the heat pump malfunctioned. Just a thought...

Stay warm and get splittin' while it's cool out! I'd rather be burning something other than gas or electricity in the long run.

Chris

 

[woodgeek]

Jim -- glad to hear that your system is working properly...maybe your 'smart' thermostat was getting a little too smart.

Jerry, I don't know who Jim is buying his $0.10/kwh juice from. To answer your question, I am buying from PECO (the big Philly utility). They have a special winter rate for folks with an elec heating system (HP or resistance) which provides a 50% discount (Oct-May) above a nominal base usage (600 kWh /month if I recall). That is, they charge me $0.15/kWh as a flat rate in the summer months, and on my nominal usage in the winter. Whatever I use over 600/mo (about equal to my actual monthly usage w/o heat or AC), costs only $0.075/kWh ! At that price, resistance heat breaks even cost-wise with oil at $2.50/gal ! (which I haven't seen since 2006-2007).

Why do they have this 'winter heating' rate? As I understand it, the utilities see their peak demand in the summer, and are running at low capacity in the winter. If they have an expensive generator with low fuel costs (e.g. that nuke plant over in phoenixville) that they need to pay off, it makes sense to run the thing more in the winter, hence a winter heating incentive. Before you get too excited, they have started making noise about discontinuing it in 2010. Whether they will remains to be seen.

And THEN I pay a 2.5 cent/kWh premium for wind power. So a lot (about half averaged over a year) of my juice is the same 17.5 cents that you are paying, but green, and I can (for a while longer) get all the 10 cent green electricity in the winter I want.