Heat pump size choice

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Mad Scientist
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#616325 27-Apr-2012 22:15

(unless there is a 'break in' period for inverters?)

timmmay

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#616327 27-Apr-2012 22:16

You must've gotten a pretty good subsidy to get a Nocria 6.0kw installed for $2400, mine's going to be $3400 and that's with a subsidy. I saw retail not so long ago, that price I'm getting isn't bad.

I'm not sure the temperate output is the main factor, 10 degrees cooler and double the airflow might be better. I know my Daikin is about 55 degrees at the output, but it just feels like a warm breeze. As long as it makes the room warm I don't much mind, they have a good reputation and they're very efficient. Efficiency and output temperature may be related - anyone know?

timmmay

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#616332 27-Apr-2012 22:21

The 6.0kw Nocria seems to cost between $2000 and $2600 at retail. That means with the $400 subsidy they're charging between $1200 and $1800 for installation. For me that's a 12m run of pipe through a ceiling, down the outside of the house, separate drain, and wiring it in to the mains board at the other end of the house.

Seems a bit expensive, but they were cheaper than anyone else around here.

Are subsidies higher down south where it's colder?

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#616334 27-Apr-2012 22:24

timmmay: Efficiency and output temperature may be related - anyone know?

Generally speaking the greater the temperature difference between indoor and outdoor the lower the efficiency. The compressor has to work harder.

Batman

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#616335 27-Apr-2012 22:28

you;re right - the the fujitsu has a much higher fan air flow ... so maybe total heat output is the same

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#616338 27-Apr-2012 22:30

my installer says fujitsu has an oversupply of heat pumps "due to the chch quake" and they're getting rid of them hence was able to get me (and everyone else that goes thru him) the special price. this is NOT subsidised as i don't qualify

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#616339 27-Apr-2012 22:31

but i do know his hourly rate is rock bottom so that may well be why

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timmmay

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#616357 27-Apr-2012 23:13

Sometimes it's who you know.

Niel

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#616395 28-Apr-2012 08:00

Skolink:
Niel: In our old house we ran it the normal way and even insulated ducting would cool down too much when going through the ceiling space.

Did you ever measure it? I did, and was surprised at how small the temperature difference was. I still want to insulate it though.

Yes, I'm an electronic engineer. We had a 40 year old house, iron roof, timber floor half meter above very wet soil, and the only insulation was in the ceiling and had completely collapsed so no use. Temperature measured with an IR thermometer I borrowed from work. Drop over 6m insulated ducting was around 7 degrees measured at night when the roof was wet and cooled down from chill factor.

I guess with clay tiles and with a sheet of plastic underneath it the ceiling space would not get as cold as ours did. We had no down lights to warm up the ceiling either ;-).

Edit: It also depends on your fan speed. Mine was slow to cut down on noise, so more time for air for cool down. But a faster fan speed just means a greater volume of air cools down a bit less - still the same amount of energy leaking out. This also explains why two similar size aircons produce significantly different temperature air, it it still the same energy just spread over a different volume of air. The same happens with your car heater/cooler (on older models).

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#616399 28-Apr-2012 08:07

timmmay: Sometimes it's who you know.

Yes. A friend-of-a-friend offered to do an installation of a 2nd hand unit including the gas for $300. A simple back-to-back installation should only be $500-$600. $1200 is a complete ripoff.

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#616419 28-Apr-2012 08:48

I got quotes from three firms, these guys were the cheapest. One firm was $4400 for the 6.7kw Nocria.

I paid around $4000 for my 7kw Failing a few years back, it was worth it. Turns out it's undersized a little though.

Ground sheets under houses makes a huge positive difference.

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#616569 28-Apr-2012 15:13

Does anyone know if running the heat pump on lowest fan setting uses less power than max setting? Please someone who actually knows no guessing ....

Coz ive been running at low fan thinking will use less power per unit time but is that true. I dont mind not having the best heat but i dont want to blow out the power bill.

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#616574 28-Apr-2012 15:16

I know in theory in an ideal world with perfect insulation if it gives max heat and the house gets to temp it will stop and use no power, whereas if you blow les heat it takes a while to get up and might never stop but that,s not the point, i'm asking power consumption at the very time its blowing at low speed.

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#616623 28-Apr-2012 16:36

Automatic speed is in theory the most efficient, because it will run at a high power when there is a large difference between set and actual temperature, then slow down as you approach set temperature.

I say "in theory" because the heat pump does not actually know what you are doing and maybe in some instance you only want the immediate surrounds warmed up so you want a slow fan speed.

So the answer is that >typically< the automatic setting is the most economical.

The reason why the slow speed for heating your house is not so economical is because the heat pump will be running most of the time (at slow speed) to try and get the temperature up while it slowly spreads to the other rooms. Rather run it at fas speed to push warm air into other rooms, get it to temperature, and then it slows down to maintain it.

There are actually 2 speeds, the one is the fan speed which we are talking about the other is the compressor speed. Traditional heat pump have a compressor that switches on/off. Moderns "inverter" heat pumps have a compressor speed control but you have no control over that. The big benefit is it extends the operation and efficiency at low outside temperature by delaying the time it takes to freeze up and require a defrost cycle, the other is it can pump the amount of heat required rather than running full throttle so reducing the wear on components extending the life of the compressor (or a pessimist would say they can use cheaper parts).

How much difference in economy is there? Hard to define. Is it worth worrying about? Probably not. You are already using less than 1/3 the power for heating compared to using any other electric heater. I would use an automatic setting and when I want low noise for watching a movie or something I can switch to low speed. And certainly go for an inverter. The extra electronics required for the design typically means they have more smarts added for "free".

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#621647 8-May-2012 13:56

Driving past Hornby Mitre10 Mega I saw they were advertising a 7kW heatpump including 'back-to-back' installation for $2699. I don't quite recall the brand but it was one I recognised (but ascociate with something else rather than heatpumps) eg Hyundai or Hitachi.

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