How (in)efficient are old non inverter "heat pumps"?

Forums › Home Workshop DIY › How (in)efficient are old non inverter "heat pumps"?

1 | 2 | 3

3239 posts

Uber Geek

Trusted

#883554 23-Aug-2013 19:04

Who is your power company?

Do you have a smart meter installed?

You maybe able to use their website to see when you're using power (for free if you have a smart meter

CPU: AMD 5900x | RAM: GSKILL Trident Z Neo RGB F4-3600C16D-32GTZNC-32-GB | MB: Asus X570-E | GFX: EVGA FTW3 Ultra RTX 3080Ti| Monitor: LG 27GL850-B 2560x1440

Quic: https://account.quic.nz/refer/473833 R473833EQKIBX

Batman

Mad Scientist
29768 posts

Uber Geek

Trusted

Lifetime subscriber

#883573 23-Aug-2013 19:57

genesis.

just got a letter today saying they are installing a smart meter by november

mentalinc

3239 posts

Uber Geek

Trusted

#883643 23-Aug-2013 21:36

You'll be able to login and see i think by hour your energy usage.
Look for large amounts used when no one is home or middle of the night.

CPU: AMD 5900x | RAM: GSKILL Trident Z Neo RGB F4-3600C16D-32GTZNC-32-GB | MB: Asus X570-E | GFX: EVGA FTW3 Ultra RTX 3080Ti| Monitor: LG 27GL850-B 2560x1440

Quic: https://account.quic.nz/refer/473833 R473833EQKIBX

Niel

3267 posts

Uber Geek

Trusted

#883645 23-Aug-2013 21:45

Our heat pump is set to 16 or 17 degrees at night and 18 to 20 degrees in the evening, which is still (just) fine for walking around in shorts and T-shirt. Our power bill for a family of 4 (2 young teenagers) is almost $300 per month (Summer is under $200 with aircon on cooling). We are in Auckland in a brand new home. At the start of Winter our power bill was over $350, but that was partly because the kids took long showers, partly because we had set the aircon to 25 degrees to make the whole house toasty.

Our old house had an old window-mount aircon. We found our power consumption was similar to running oil fin heaters, but with oil fin heaters we barely broke the cold where as with the heat pump we were comfortable. Running cost ends up the same, comfort is significantly improved. With improved comfort also goes improved health (physical and emotional).

You can never have enough Volvos!

mclean

581 posts

Ultimate Geek

Subscriber

#884526 26-Aug-2013 10:39

joker97: I have a giant Mr Slim Mitsubishi heat pump rated 2.4kW by the internet but says 3.2kW on the outdoor unit and the model number is PUH-3KVA.

Might that be PUH-3VKA??

The PKH indoor units were wall-mounted, not ceiling-mounted. Most likely match for your outdoor unit would have been PKH-3FKA. These were 2002-2004 vintage non-inverter units.

Batman

Mad Scientist
29768 posts

Uber Geek

Trusted

Lifetime subscriber

#884530 26-Aug-2013 10:43

Are they seriously less efficient or not really?

mclean

581 posts

Ultimate Geek

Subscriber

#884581 26-Aug-2013 11:52

joker97: Are they seriously less efficient or not really?

Yes, for sure. For your unit the rated heating/cooling COP's were 2.43/3.00 respectively. For a modern equivalent with inverter drive they would typically be 3.7/3.6.

But that's only part of the story. Inverter units can turn down and operate at part capacity, and that's how they run most of the time. In this condition they are much more efficient than the rated COP's. Your unit can't turn down - it can only goes at full capacity or off. Some manufacturers these days quote a sort of "annual COP" which takes account of part-load operation, but you won't find this number for older units to compare.

The other thing is your units use R22 refrigerant, which is bad form these days!

COP for cooling is called EER these days.

Quic Broadband

Move to New Zealand's best fibre broadband service (affiliate link). Free setup code: R587125ERQ6VE. Note that to use Quic Broadband you must be comfortable with configuring your own router.

Batman

Mad Scientist
29768 posts

Uber Geek

Trusted

Lifetime subscriber

#884587 26-Aug-2013 12:05

Hmm ... That makes total sense it runs at 2.4kw or whatever it rates at all the time that is on. For some reason when the comoressor is off (20% of the time of it being on) it blows cold air!

Hammerer

2476 posts

Uber Geek

Lifetime subscriber

#887589 31-Aug-2013 21:56

joker97: the point is the combined heatpump on time is half in this house compared to the old house.

it's tropical without any heating. the heatpump is only on when there is no sun. and on low fan. (ie the heatpumps are not doing work the whole time they're on because the house retains heat a lot better)

in our old house we had 2 x 6kW heatpumps (COP4) going on most of the day on medium fan without making any headway into the house heating (ie the compressor is doing work the whole time it's on).

You said you're spending about $1,000 over two months. We used $900 over the last two months. It sounds like our usage should be similar except that you're heating a larger area:
We've got a 6kW heat pump going 24 hours at about 22C for an invalid. Thankfully it is in the best insulated part of the house.
We have an 8kW heat pump in the main living area. It runs up to 14 hours a day but mostly 4-6 hours for the early morning and evening. Both are a few years old with COP of 4. We have lots of windows so the house heats up on sunny days but is cold on cloudy days.

Re fan settings, "low fan" doesn't usually mean it is working less than "medium fan". It is possible that using "low fan" is costing you because the heat pump can't move the heat as efficiently due to the low airflow. Most heat pumps work best if they are set to "auto fan" because they are usually programmed to work efficiently.

Batman

Mad Scientist
29768 posts

Uber Geek

Trusted

Lifetime subscriber

#887635 31-Aug-2013 23:05

thanks. shouldn't an inverter be able to regulate the amount of work it needs to do? so if I set to low fan i'm hoping the thing is working at an efficient part of the curve? hmm ...

Niel

3267 posts

Uber Geek

Trusted

#887689 1-Sep-2013 08:21

The fan speed on the remote is for the internal unit, depends on if you want the air to be quickly/evenly heated up or if you want to cut down on "wind". At slow fan speed the heat pump will take longer to get the room up to temperature, so inefficiencies will waste power for longer (just like when you run your tumble dryer on low heat).

The external unit (fan and compressor) will run at the most suitable point for whatever setting you have on the internal unit, you do not have control over the external unit. But a bad setting on the internal unit means the external unit needs to either run longer or work harder.

You can never have enough Volvos!

Batman

Mad Scientist
29768 posts

Uber Geek

Trusted

Lifetime subscriber

#887696 1-Sep-2013 08:45

good to know!

just a small question - do you think changing a non inverter in my case (2.4kW outdoor unit) trying to heat a big space) to 2 super efficient 4.4COP heat pump ($2300 each - sounds like 3 months' bill!) would pay off fast?

timmmay

20582 posts

Uber Geek

Trusted

Lifetime subscriber

#887711 1-Sep-2013 09:38

2.4kw trying to heat a large area would always be running at 100%, where it's less efficient. A larger unit would run more efficiently, and would get the room up to temperature properly, but I don't know that the bill would be less - it could be more if the room never gets up to temperature now.

I paid $4K or so installed for a decent 10kw Fujitsu Nocria. It works well, running costs are good, but it's pretty loud. When we're watching TV it has to be on super quiet, and this is with a good 5.1 surround system.

Handle9

11394 posts

Uber Geek

Trusted

Lifetime subscriber

#887713 1-Sep-2013 09:45

joker97: good to know!

just a small question - do you think changing a non inverter in my case (2.4kW outdoor unit) trying to heat a big space) to 2 super efficient 4.4COP heat pump ($2300 each - sounds like 3 months' bill!) would pay off fast?

No, you are probably looking at a 5-10 year payback. If you run the unit 8 hours a day for 200 days you get a cost of $360 per annum for you 2.4 kw unit at a derated COP of 2 and an energy cost of 25c per kWh

Cost per annum = (power rating of unit x hours run x days run x cost of power)/COP

Even if a new unit reduces your energy cost to zero the difference will still be 6 years.

It will be costing more than this to run the unit as it will be having to defrost alot in Dunedin but that won't change a great deal with a new unit.

Niel

3267 posts

Uber Geek

Trusted

#887790 1-Sep-2013 14:26

Everything is priced with a 5-10 year payback, unless you get a super deal through a mate. This is for insulation upgrade, solar heating, double glazing, whatever. One of the few exceptions (lately) is LED light bulbs where you have a 6 month payback if used 5h per day (at ~$20 per bulb).

BTW, I have a window mounted box aircon ~3kW in East Ackland if anyone wants it. Small donation would be appreciated, but I'd rather give it to someone that will use it than throw it away. Works well except around October/November when it gets really cold and the aircon freezes up. PM me if interested, or else I'll advertise it when I clean up the garage in a couple of months. I've mounted it in our old house by unscrewing a window and filling the gap, no need to cut holes.

You can never have enough Volvos!

1 | 2 | 3