prog. therm. and heat pump questions

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What is the time constant as that 60K heat pump warms up? Would it ever reach steady state and a COP of 3? Well maybe when it was running after the setback period ended.
60,000 steady state heat output, 20,000 load each hour hmm, wonder how many times that will cycle on and off drawing LRA? Well if a dog year is 7 years, a Nick year must be 3 years.
Maybe assume it takes 15 minutes to stabalize and work backwards from there for your time constant.
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Why would anybody ever install a heat pump system?
Another friend of mine's heat pump just bit the dust here at -20C. Going to take weeks to get a part for it. Pretty expensive portable electric heating going on in that house right now.
That makes 9 heat pumps that will be removed of my aquaintenances in the last few years now.

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Its cheaper than heating with other forms of electrical heating.

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John P.. Bengi wrote:

Where I live, according to weatherbase.com, the lowest temperature ever recorded in the last 48 years is -18C (-2F). In an average year, there are only 19 days when it even dips below 0C (32F). Our average snowfall each year is 0.9 inches.
So, here, heat pumps wouldn't have cold temps to deal with. On the other hand, plain old resistive heat is really not that expensive, so heat pumps might not even be worth it.
- Logan
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John P.. Bengi wrote:

Air source getting yanked out of Southern Ontario?

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Slowly but surely, I guess. I become more glad with each year I didn't indulge.
With NG 1/3 of the price of electricity here, the reliability very poor, and a complete backup system required anyway, I doubt they will be selling many of them anymore.
Sounded good in the 80s though.

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Air source were useless in NW Ontario, ground source worked. John P.. Bengi wrote:

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I also know of two ground source units that have bit the dust and were never replaced due to costs compared to gas here. I have heard longer life with the ground source units though. The air source units had too many freeze up problems with rainy freezing weather then the "defrost" cycle had to be brought in and the unit was never big enough to handle the BTU load anyway so the backup was cutting in from timte to time.

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I only sold ground source in areas where gas was not available. Compared to propane, oil and straight electric they are viable.
I had an opportunity to sell one in a gas area and it would have saved about $100 per year over high-efficiency gas, but talked the customer out of it as he would have spent perhaps 6 grand more than the gas furnace with central ac.
John P.. Bengi wrote:

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That was honest of you.

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snipped-for-privacy@ece.villanova.edu wrote:

an ok ballpark analysis for comparative purposes. I wouldn't value the actual numbers beyond their ability to provide inequalities (More than/less than). They are too ambiguous. Still I don't see yet where we are in disagreement. Maybe you weren't trying to disagree. I dunno.

Sure it can, else there wouldn't be an economic balance point. As the ambient drops the suction pressure drops too, mass flow is reduced, thus he capacity is reduced as ambient temp drops. Runtimes are also longer and take place with reduced volumetric efficiency, thus COP drops as well. At what point would this curve level off? Wouldn't it continue to fall right on through the 1:1 mark? At 0K (absolute zero) the COP would theoretically be 0:1. Assuming a COP of 2:1 at 40F thus we can thus interpolate a COP of 1:1 at an ambient temp somewhere between absolute zero and 40F.

Thanx, very good site. The rim deflector is a must have item. :)
hvacrmedic
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Seems to me it has to be greater than 1:1 for heating, since the compressor heat ends up in the house. This requires good defrost control: turn off the compressor and run the outdoor fan if the outdoor coil is about to freeze, and turn off the whole shebang if the outdoor temp is less than 32 F. IIRC, Carrier did experiments with heat pump coils covered with 2" of ice, and the COP was still greater than 1.
http://www.cleanbutt.com/PRODUCT.ASP , with optional wireless remote control.

The remote adds $100. EXTREMELY obese people find it useful.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Not all of it, unless the compressor is insulated. Also there are the controls (contactor, etc.), condenser fan, crankcase heater, RV coil, and defrost cycle to take into account. I wonder if Carrier fudged too?
hvacrmedic
This requires good defrost control: turn off the

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snipped-for-privacy@ece.villanova.edu wrote:

You have way too much time on your hands....:-)
Marsha/Ohio
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A couple of things to mention.
1) The COP of the heat pumps I normally install is greater than 3.5 when the outdoor temperature is 47 degrees when heating and greater than 2.5 at 17 degrees outdoor temperature when heating. The COP of strip heat is ALWAYS 1.0. In my area it does not often get below 20 degrees outside temperature. Even at 0 degrees the COP of air to air heat pumps manufactured in the last 20 years will be at least 1.5. More efficient units will have a COP of 1.7 to 2.0 under the same conditions. Look it up in your engineering data guys.
2) The heat output of air to air heatpumps drops as it gets colder outside while the heat load of the house goes up under the same conditions.
3) The balance point of most properly sized heat pumps is around 35 degrees outdoor temperature. That means that most properly sized heat pumps without heat strips cannot heat the house to 75 degrees indoors when it is below 35 degrees outdoors. Therefore when it is below 35 degrees outdoors, such as at night, the compressor will run constantly and the heat strips will cycle on & off to maintain comfort.
4) As an experiment, I installed a setback thermostat in my house 10 years ago. I locked out the strip heat and programmed the temperatures at 68 degrees setback at 11:00 PM and 75 degrees setup at 5:00 AM. The heat pump started running constantly at 5:00 AM and did not bring the temperature back up to 75 degrees till after 5:00 PM. The day time temperatures were in the mid 50s and the nighttime temperatures wewre in the mid 20s.
5) Setback thermostats were originally designed to save money operating oversized fossil fuel furnaces. If your heat pump is properly sized by the cooling load, it will not be able to recover in a reasonable amount of time whithout using the strip heat. Therefore, you will either be cold much of the time in the winter or your electric bill will INCREASE with a setback thermostat. NOTE: If your heat pump is oversized the setback penalty will be reduced, but the fact it is too big will reduce the effective efficiency all year long. NOTE also that setback thermostats WILL save money in the cooling season, even when the heat pump is properly sized.
For what it is worth. Measured data, not guesses.
Stretch
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Note to the people who will raise cain about my post: I can email you PDFs of some Lennox engineering data if you wish to check my figures. If you are Lennox or Carrier or Trane dealers, you should have the same sort of data available to you in printed form.
Stretch
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One obvious approach would be to have two, use one in the summer and both in the winter.

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Be a little windy inside in the winter, but you could size one system to the cooling load, look at its winter heat output then size the second one to make up the difference .
You would eliminate heat strips for maintaining comfort but you would still need heat strips to recover from the setback. If you want to live with the lowered temperature while the system is trying to recover, why set it back in the first place? Wear wool socks, bunny slippers, long underwear and a sweater all winter.
Making the second heat pump large enough so that the combined heat output was triple the design heat load, would eliminate the heat strips on the set back but you have the problem of the second system short cycling all the time except when revovering from the setback.
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Why not dual fuel? HP and whatever is the cheapest fuel for the backup.
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Steve Scott wrote:

Dual fuel is practical, seems the arguement is being to setback heat pumps.
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