prog. therm. and heat pump questions

[nicksanspam]

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.

with optional wireless remote control.

The remote adds $100. EXTREMELY obese people find it useful.

Nick

[RP]

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

[John P.. Bengi]

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.

up? Would it ever

was running after

hour hmm, wonder how

Well if a dog year

work backwards from

[Rod Speed]

John P.. Bengi wrote

Its cheaper than heating with other forms of electrical heating.

[Marsha]

You have way too much time on your hands....:-)

Marsha/Ohio

[Logan Shaw]

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

[Abby Normal]

Air source getting yanked out of Southern Ontario?

[John P.. Bengi]

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.

[Abby Normal]

[Stretch]

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

[Stretch]

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

[John P.. Bengi]

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.

worked.

of

message

news: [e-mail]...

Ontario?

[Rod Speed]

One obvious approach would be to have two, use one in the summer and both in the winter.

[Abby Normal]

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:

[Abby Normal]

Yep the lower the temperature source the lower the heat output.

Yep not arguing there, 75 is on the high side tho for a winter set point. A setpoint of 68 to 70 set back to 60-65 overnight will be similar tho. Running without heat strips will take a long time to bring temperature back up and would need the help of the sun, unless of course the heat pump is sized for triple the heat load .

I have seen ground source sized to the heating load in Canada and end up being 100% oversized for cooling. In this situation the summer humidity was still low enough as to not be problematic and create an overly humid, mold condusive indoor environment in the summer.

A system sized for the full heat load, in a warmer climate with a hot humid summer most likely will be oversized for cooling and enf up with high indoor RH in summer. Just imagine what something sized for 3 times the heating load will do in summer.

No arguement there. A unit oversized to the point of not needing heat strips to recover from a setback would short cylce in heating as well as cooling.

[Abby Normal]

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.

[Steve Scott]

[Abby Normal]

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

[Rod Speed]

Abby Normal wrote

Yeah, that's what I meant.

The other possibility is to stop the setback well before you get up.

You could obviously have 3 systems but thats not likely to be economic unless you are using close to free surplus systems.

[Abby Normal]

When it is sized to the load the problem is it would only shut off for an hour or two as the house cooled, then it would run steady until after the sun came up to catch up. No real point in setting back.

The only way set back works with a heat pump is if it is grossly oversized. All that accomplishes is set back without auxiliary heat. It would short cycle inefficiently except for when it was trying to recover from a set back.

In an environment with an ambient dewpoint above 60F there will be problems with a grossly oversized system in cooling mode.