Heat Pump - How to use efficiently?

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tdgeek

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#198257 2-Jul-2016 11:00

Long time log fire user, now have moved, and have two heat pumps.

I assume that the higher the temp differential the higher cost, i.e. 10 outside, heat pump set to 20 is cheaper than 4 outside, heat pump set to 24. Obvious I guess.

Downstairs there are two living rooms, and kitchen, the living room where the TV is takes a bit longer to warm up.

So, is it better to heat at say 22 on low fan, or say 18 on high fan. To, 1) reduce costs, and 2) to promote more air movement?

I am a heatpump noob.

Edit: Fujitsu Inverter, Cooling 7.4kW heating 8.5kW

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#1584527 2-Jul-2016 11:09

Funny we were talking about this at work yesterday. I think most people have their own preferred way of using it. For me I generally keep it at 22 on heat in the colder months, with the fan on quiet unless it's really nipply then I turn it up a notch, but because of our lounge the fan is quite an obtrusive sound.

My mum uses it in what i would call "the wrong way": she just puts it on 30 and blasts the lounge with high fan for as long as it takes to warm the room then turns it off. I can't convince her this isn't the best option :)

I think our heat pump is in the wrong spot though. Where our couch is - one end gets the warm air, one end gets the cold under draft. But it's a rental so we make do.

On the really bad polar blast nights we might have a radiator going on low just to provide consistent help with the chill.

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#1584532 2-Jul-2016 11:17

gehenna:

Funny we were talking about this at work yesterday. I think most people have their own preferred way of using it. For me I generally keep it at 22 on heat in the colder months, with the fan on quiet unless it's really nipply then I turn it up a notch, but because of our lounge the fan is quite an obtrusive sound.

My mum uses it in what i would call "the wrong way": she just puts it on 30 and blasts the lounge with high fan for as long as it takes to warm the room then turns it off. I can't convince her this isn't the best option :)

I think our heat pump is in the wrong spot though. Where our couch is - one end gets the warm air, one end gets the cold under draft. But it's a rental so we make do.

On the really bad polar blast nights we might have a radiator going on low just to provide consistent help with the chill.

Cute!!

I need to read the manual, I see there is a swing thing to move airflow, but the wife and 17yo daughter just turn it on high, who cares!

I'm even wondering if a floor fan that can rotate low, might be a good option to help air movement to the formal living room?

The kitchen/living room is about 7mx6m, heat pump is there, then next to that with a 1.5m walkthrough is dining room and living room, about 7m x 5m (DR is 1.5m narrower)

Or, put heating on sooner?

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#1584561 2-Jul-2016 11:35

I LOL every time I see someone heating a room with the heatpump set to 30°C or cooling at 16°C

It's generally a good litmus test for technological ineptitude.

timmmay

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#1584569 2-Jul-2016 12:06

Here's how you use a heat pump.

1. Set the heat pump to the desired mode (heat, cool, rather than auto)

2. Set the fan to auto, for maximum efficiency, or lower the fan speed if you prefer, but it will be less efficient

3. Set you desired end state temperature. The outside temperature is irrelevant.

When you don't need it, turn it off. When you need it, turn it on again. If you don't need it for a short time (an hour) it may be worth leaving on, but if it's all day then turn it off.

A heat pump is more efficient to heat if it's warmer outside. So if it's 10 degrees at 4pm and 0 degrees at 7pm it's probably worth having the timer turn it on at 4pm. If you're on a variable rate, like Flick electric, then the situation is a bit more complex - in that case you avoid peak time (16:30-19:00 weekdays usually), pre-warm, and take advantage of night rates if appropriate.

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#1584570 2-Jul-2016 12:06

tdgeek:

Long time log fire user, now have moved, and have two heat pumps.

I assume that the higher the temp differential the higher cost, i.e. 10 outside, heat pump set to 20 is cheaper than 4 outside, heat pump set to 24. Obvious I guess.

Downstairs there are two living rooms, and kitchen, the living room where the TV is takes a bit longer to warm up.

So, is it better to heat at say 22 on low fan, or say 18 on high fan. To, 1) reduce costs, and 2) to promote more air movement?

I am a heatpump noob.

Edit: Fujitsu Inverter, Cooling 7.4kW heating 8.5kW

Does it state what the EER and COP ratings are? Just interested, as I've been looking at his myself

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#1584572 2-Jul-2016 12:11

I have the one in the Lounge on Auto 22 Degrees all year round with a timer to turn off at 11pm (Incase we forget).

The one in the Bedroom is on Auto 21 Degrees 8pm - 7am all year round.

Hmmmm

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tdgeek

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#1584581 2-Jul-2016 12:19

James Bond:

tdgeek:

Long time log fire user, now have moved, and have two heat pumps.

I assume that the higher the temp differential the higher cost, i.e. 10 outside, heat pump set to 20 is cheaper than 4 outside, heat pump set to 24. Obvious I guess.

Downstairs there are two living rooms, and kitchen, the living room where the TV is takes a bit longer to warm up.

So, is it better to heat at say 22 on low fan, or say 18 on high fan. To, 1) reduce costs, and 2) to promote more air movement?

I am a heatpump noob.

Edit: Fujitsu Inverter, Cooling 7.4kW heating 8.5kW

Does it state what the EER and COP ratings are? Just interested, as I've been looking at his myself

Fujitsu ASTA24LCC inverter heat pump/air conditioner 7.4kW cool/8.5kW Heat

Price / Specials:

Dimension mm (length/height/depth);998/320/228
Star rating heat/cool:5 / 4
Efficiency:COP Heat 3.51/EER Cool 3.01
Noise levels (quiet/low/med/high): 32/36/41/47
Features: 6 year warranty, high wall inverter
Floor area: Up to 75m2

Ok? Fair? Average?

tdgeek

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#1584582 2-Jul-2016 12:22

timmmay:

Here's how you use a heat pump.

1. Set the heat pump to the desired mode (heat, cool, rather than auto_

2. Set the fan to auto, for maximum efficiency, or lower the fan speed if you prefer, but it will be less efficient

3. Set you desired end state temperature. The outside temperature is irrelevant.

When you don't need it, turn it off. When you need it, turn it on again. If you don't need it for a short time (an hour) it may be worth leaving on, but if it's all day then turn it off.

A heat pump is more efficient to heat if it's warmer outside. So if it's 10 degrees at 4pm and 0 degrees at 7pm it's probably worth having the timer turn it on at 4pm. If you're on a variable rate, like Flick electric, then the situation is a bit more complex - in that case you avoid peak time (16:30-19:00 weekdays usually), pre-warm, and take advantage of night rates if appropriate.

Great reply, thank you. I'm on Genesis, Ill ask them the peak rate and review our plan

Cheers

timmmay

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#1584584 2-Jul-2016 12:28

My 3 year old Fujitsu Nocria is really quite loud, but I chose it mostly based on efficiency. My 5 year old Daikin is much quieter, slightly less efficient. The smaller the heat pump the more efficient it is, but if you run a small heat pump at 100% it won't be running at its most efficient. On the other hand a larger unit with a lower COP that's not running at 100% should use less power for the same heat.

Jase2985

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#1584827 2-Jul-2016 20:12

a heal pump is least efficient on a cold night right around the due point in the 1-5deg range. so someone in Hamilton will have a less efficient heat pump than say someone in central otago where it is -10deg outside.

If your house is well insulated and you have double glazing it may be more efficient to leave it on all the time, than to turn it on and off.

timmmay

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#1584861 2-Jul-2016 21:12

Jase2985:

If your house is well insulated and you have double glazing it may be more efficient to leave it on all the time, than to turn it on and off.

This is false according to every reputable reference I've found, including this one. Turn heating on when you need it, or far enough in advance that things are warm enough, but don't leave heating on all the time.

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#1584904 2-Jul-2016 22:42

timmmay:

This is false according to every reputable reference I've found, including this one. Turn heating on when you need it, or far enough in advance that things are warm enough, but don't leave heating on all the time.

Yep, the heat lost from a house is directly proportional to the temperature difference maintained, so only maintain that difference when you need it. Same goes for spa pools

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#1584911 2-Jul-2016 23:07

You are best to leave the fan speed on auto, assuming the noise isn't too intrusive (lower fan settings hurt efficiency).

Otherwise just set it to the temperature you want and leave it alone. Higher temperatures cost more...

We have ours set on a time to come on from 6:10 to 8:10 each morning, so the house is nice an warm when we get up (we have an cheap oil heater in our bedroom, with a plug in digital thermostat (the built in one gets to much feedback from the heater itself) and timer, that keeps our bedroom warm at night).

In the evening, we just turn it on when we get home, and turn it off before we go to bed.

jonathan18

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#1584947 3-Jul-2016 06:16

Scott3:

You are best to leave the fan speed on auto, assuming the noise isn't too intrusive (lower fan settings hurt efficiency).

Otherwise just set it to the temperature you want and leave it alone. Higher temperatures cost more...

We have ours set on a time to come on from 6:10 to 8:10 each morning, so the house is nice an warm when we get up (we have an cheap oil heater in our bedroom, with a plug in digital thermostat (the built in one gets to much feedback from the heater itself) and timer, that keeps our bedroom warm at night).

In the evening, we just turn it on when we get home, and turn it off before we go to bed.

I'd support this approach as well. When we first put in the ducted system I farted about with various settings, but have settled on it starting up at 6 each morning (heard it kick in a few minutes ago!) with the fan set to auto, turning off weekdays at 8.20 but later in weekends. Other times turn on as needed. Sometimes we'll run it at night, but I reckon it disrupts my sleep. Occasionally I'll run it at the start with the fan at a higher speed just to speed up the air distribution (key when you're attempting to get a whole house heated evenly), but always return it to auto otherwise it leads to a cycling of too hot/too cold.

One of the earlier posts mentioned some use that "technique" of running it at a really high temperature for a period then switching it off - personally, I've found this often comes from a real confusion as to how thermostats work. Surprised at how many people think setting the temp higher will heat up the space quicker!

timmmay

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#1584954 3-Jul-2016 08:10

I wonder it heat pumps have various levels of efficiency, and if they gap between desired and current is large they run in "high output low efficiency" mode, if it's small they run slower and more efficient. I've noticed that if the difference between current and target temperature is high the indoor unit is a lot louder, with my Fujitsu.

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