Electric Heat Pump ?'s

[BigJon3475]

Originally Posted by Threerun

THX! I think I could reasonably handle a Man J load calculation. Most importantly is finding out from some experts if those mini's would even work here.

Crap. I had a long reply that I accidentally "x'ed" out of. I just don't have it in me to try to repeat it.

Okay. Go here:

Welcome to Goodman Manufacturing

User Name: goodman
Password: dealer

Toolkit > Goodman Dealer Tool Kit > Product Tools > InfoFinder > Type in GSZ130181 in the search field.

This is a typical R-410a HP that is 1.5 tons for cooling with an 8 HSPF (Heating Seasonal Performance Factor). I'd attach the file but it's too large. There are other examples of larger systems and their performances.

You'll want to go to the second page of the results in your search. It will be called Spec Sheets. Click on the first file with that name and go down to page 22 (you'll have to rotate). You should be looking at:

Expanded Heating Data

GSZ130181A* / AR*F182416**

This will give you the performance at certain outdoor temperatures. It starts at 65°F and goes down to -10°F.

MBh - Million BTU an hour
ΔT - Delta Temperature (The temperature difference of the incoming and exiting air)
kW - Kilowatt (The power used by the HP at that temperature)
Amps - Pretty straight forward (Dividing kW by Amps will give you the voltage required)
COP - Coefficient of Performance (This is the efficiency of the unit meaning that for every 1 watt of power it transfers x BTU. For reference all electric backup heat -- called resistance heating -- has a COP of 1. For every 1 watt of power it produces 3.413 BTU.)
EER - Energy Efficiency Ratio
Hi PR - High Pressure (Not something you really need to know unless you're servicing the system.)
Lo PR - Low Pressure (Not something you really need to know unless you're servicing the system.)

You should immediately notice that for this combo the COP at -10°F is 1.22. That means that for every wat used it will transfer 4.16386 BTU. It's more efficient than electric backup heat even at those temperatures. It wouldn't be till you got into the mid negative 20's that it would be equal. At that point there really isn't enough heat to do you much good.

Now here comes the confusing part. Obviously the colder it is outside the faster heat will leave your home, because of the higher delta, and the higher the infiltration rate from wind because wind is more dense at colder temperatures which is why colder wind "feels" like it's pushing you harder at the same velocity as it would at higher temperatures.

This is where the load calculation comes in because it will give you the temperature for which you will be at most of the time and that means you won't be designing for maximum or minimum situations. You'll have to take off some clothes or put more just to save on the energy bill. In other words your HVAC system "won't be keeping up" and this is where everyone gets confused. If you design the system to keep up on 110°F days you'll be way over-sized and wasting lots of money on both usage and the equipment cost itself.

Digest that and let me know if you have any more questions.

(By the way I thought it might be best to go ahead and post this because it just might help someone else.

Also, try to ignore brand names and go for the quality of the instillation. Too many people think having a system that "can't be stopped" means you're getting the best you can buy. That's subjective to the person and the amount of money they have. That system that "can't be stopped" actually has poorer performance data than el cheapo Goodman does. That doesn't mean that manufacturer isn't good you just pay for the higher quality materials when both systems will last you well over 15 years if properly serviced and installed.)

[BigJon3475]

Unless you have a degree in mechanical engineering, thermodynamics or HVAC/R, it would be best to let someone that does them for a living do this.

Residential HVACR

ACCA Checklist - https://www.acca.org/Files/?id=68

[Threerun]

The extent of my HVAC knowledge lies with me helping my Dad. He owned a commercial HVAC/refrigeration company. We dealt with commercial applications mainly, but a few residential installs here and there. Of course that was in the dark ages, when HP's were not favored and he could buy freon without EPA certification and scrutiny, ha-ha.

That being said, I was mostly assisting with install / turning wrenches, but I understand the terminology. However I'm a commercial banker by trade, so take that all with a grain of salt, lol.

I think I could muddle through and get as close as any do it yourselfer could.

[Threerun]

Would a 'formal' load calc even be practical given I am dealing with ductless systems? Any calcs based on duct distribution / sizes / velocity are moot. I have to deal with CFM vs. cubic air mass I believe.

[BigJon3475]

Originally Posted by Threerun

Would a 'formal' load calc even be practical given I am dealing with ductless systems? Any calcs based on duct distribution / sizes / velocity are moot. I have to deal with CFM vs. cubic air mass I believe.

Manual J determines your house's heat gain/loss calculations. It has nothing to do with Manual D except that it gives the baseline for what each room requires from your centralized system.

I was trying to give you info to play with.

Did I misunderstand the fact that you were interested in if a HP can do anything for you with your negative temps?

Ductless systems perform the same way and you can easily just focus those systems on a single room in which you would be better off in all circumstances. You remove the duct losses and the fact that you're trying to heat the whole house as opposed to a single room.