Heat Pump - How to use efficiently?

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gordy7
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#1584964 3-Jul-2016 09:08

Jase2985:

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.

Can you explain further?

On first reading I found what you were saying confusing mentioning dew point and actual temperature.

My first interpretation:

Hamiltion with higher humidity reaches dew point fairly early on (say +1C perhaps), whereas Otago with lower humidity does not reach dew point until about -10C.

I guess the dew point determines roughly when the outside heat pump coils freeze.

Am I on the right track?

Gordy

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timmmay

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#1584966 3-Jul-2016 09:11

Gordy7:

Can you explain further?

Consumer explains it quite well. Related info here about defrost cycles (though it's trying to sell something so grain of salt).

ben28

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#1585546 4-Jul-2016 12:28

Fan on auto, mode on heat, set your end state temperature , then leave alone is most efficient.
If you are out for a couple of hours on low a heat pump may only use 1 kW of power so maybe best to just leave going.
I was told by sales person to just heat the room it's in, then when it gets to desired temperature open door to any other areas you want the heat to seep out to.
I've read people stating that it's more efficient to keep a room at a stable temperature , rather than letting it go cold then heating to a desired temperature. They mention things like furniture soaking up the heat, and if you let the, cool you just need to reheat the unit. I'm not sure , maybe this applies more to a well insulated house in the middle of Canada rather than nz.
Be sensible , like closing curtains, shutting off rooms not used etc

Kickinbac

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#1585720 4-Jul-2016 16:12

Many newer heat pumps now have an occupancy sensor. If the room is empty for say 20 minutes, they start saving energy by raising or lowering the set point (say from 22 degrees back to 20 degrees in heating). When someone enters the room it returns to the original setting.

At work I quite often leave my heat pump running when I go out but reduce the temperature from 22 to 20 degrees. It heats up a lot quicker when I get back if it's not so far from the setpoint. It's old so no occupancy sensor. I don't pay the power bill but I hate wasting energy.

If you buy a heat pump with the best COP available you get more heat for the energy used.

timmmay

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#1585739 4-Jul-2016 16:48

Kickinbac:

Many newer heat pumps now have an occupancy sensor. If the room is empty for say 20 minutes, they start saving energy by raising or lowering the set point (say from 22 degrees back to 20 degrees in heating). When someone enters the room it returns to the original setting.

At work I quite often leave my heat pump running when I go out but reduce the temperature from 22 to 20 degrees. It heats up a lot quicker when I get back if it's not so far from the setpoint. It's old so no occupancy sensor. I don't pay the power bill but I hate wasting energy.

If you buy a heat pump with the best COP available you get more heat for the energy used.

People have quoted references earlier in this thread which unfortunately disagrees with your opinion.

First, heat loss is proportional with the difference between indoor and outdoor temperature. So by leaving your heat on all the time you lose more heat, and will cost you more. Comfort is better.

The smaller the heat pump, the higher the COP / efficiency. However a small heat pump with a small outdoor unit running at capacity is going to be less efficient than a large heat pump running at 50%.

Kickinbac

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#1585949 4-Jul-2016 21:20

timmmay:
Kickinbac:

Many newer heat pumps now have an occupancy sensor. If the room is empty for say 20 minutes, they start saving energy by raising or lowering the set point (say from 22 degrees back to 20 degrees in heating). When someone enters the room it returns to the original setting.

At work I quite often leave my heat pump running when I go out but reduce the temperature from 22 to 20 degrees. It heats up a lot quicker when I get back if it's not so far from the setpoint. It's old so no occupancy sensor. I don't pay the power bill but I hate wasting energy.

If you buy a heat pump with the best COP available you get more heat for the energy used.

People have quoted references earlier in this thread which unfortunately disagrees with your opinion.

First, heat loss is proportional with the difference between indoor and outdoor temperature. So by leaving your heat on all the time you lose more heat, and will cost you more. Comfort is better.

The smaller the heat pump, the higher the COP / efficiency. However a small heat pump with a small outdoor unit running at capacity is going to be less efficient than a large heat pump running at 50%.

oo

I'm not advocating leaving a heat pump on 24/7, so much depends on your particular home, climate, how long you are at home, what you are willing to pay for energy, comfort etc.
I'm also just advising that there are models that have energy saving features available if you do leave them running. Obviously lowering the temperature in a room lowers the difference between indoor & outdoor temperature. The closer the temperature differential the slower the heat loss.
I didn't say anything about a smaller heat pump. All heat pumps have a COP rating, buy the most efficient one that is the correct size for your house otherwise it's not going to work effectively.

Dyson

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chimera

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#1586534 5-Jul-2016 16:55

Just tagging onto this post...

I'm looking for a heat pump primarily to heat my kids rooms. Their rooms are at the end of a longish hallway. At the end of the hallway it opens out to about a 1.5-2m square-ish area, off that space are 3 doors into the 3 bedrooms (so quite close together). I had a heat pump specialist guy come around, and after I turned down the ducted system they were offering due to it being a squizzilion dollars (we have gas fireplace in living area etc so didn't feel the need) I asked what the next best option is; he said probably a floor console that is mounted low on the wall in the 2m square space that sits just outside the bedrooms and have it pointing roughly towards the bedroom door openings. He said a high wall unit is good for a large opening / large room but no good for a hallway, makes sense. He suggested about 1kW per room (average size bedrooms, 3.5m x 4m or so) so the 3.6kW model would suit.

So, does anyone have a floor console unit and have any opinions about them? Good bad or indifferent? Suggestions?

Also, anyone know of any specials on in the Auckland area for a model like this?!

timmmay

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#1586542 5-Jul-2016 17:03

A friend has a floor model of heat pump, it seems quite effective. 3.6kw is fairly small, my wall mounted one for the lounge / sleeping area is around 10kw, but bedrooms don't need that much heat especially in a smaller house. We use a 500w oil heater in each bedroom, but only after the big heat pump has heated everything up already.

richms

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#1586620 5-Jul-2016 19:01

IME a heatpump is not cost effective in a bedroom for heating. That is also the reason that was given to a friend who was looking to milk his parents community service card inorder to get one installed when they declined a bedroom install, and why I couldnt get one for cheap back when I had the card too.

I have a 3.2 kW in the bedroom, mainly for cooling.

In winter is is ok at heating when it is really cold, but when the room gets warm it starts to cycle on and off, averaging stuff all usage. A small oil heater will be quieter and cost less to buy, the savings in power of the heatpump probably never covering the cost of installing it. Perhaps if you are planning on being there for a long time. But before you consider the heatpump get the insulation and windows sorted out, those have no limited lifespan or operating costs like a heatpump and will give as much or more savings.

Richard rich.ms

Scott3

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#1586818 5-Jul-2016 21:55

Heat-pump heating for kids bedrooms are kind tricky to make work.

Ways to do this:

Ducted system (One company will supply & install a Panasonic 7.0kW (heating) ducted system to 4 bedrooms for $6,449)
Individual high wall units (smallest Panasonic unit has a 2.8kW heat output, and is worth around $1200+install (say $500)) Looking at $5100 for there rooms.
Multi split system (three indoor unit, one outdoor units - sounds good, but would expect this to cost similar or greater than individual units.
Hydronic system - Radiators (or underfloor) - Rare to be heat pump driven in NZ, probably only makes sense of you have other areas underfloor heated.

In regards to putting one heater in the hallway, obviously this only works if the doors are open. Also note that heat pump's don't thermosiphon as well as other heating, as they emit a lot of only very slightly heated air (as opposed to fires and gas heaters that output a small amount of very hot air). Should be a lot better than nothing though... (perhaps somebody who has a heat pump in a hallway can comment).

We just have a cheap 1kW warehouse oil heater in our bedroom, hooked up to an external plug in timer & external plug in thermostat. It comes on from 8pm to 7am, only if the room is cold. Given we are with flick, and nightime electricity is the chepist, this could be a cost effective option.

timmmay

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#1586868 6-Jul-2016 07:00

I have a big heat pump in the lounge. The air has to go around two corners, a 180 degree bend, to get into our bedroom. It does get in there, reasonably effectively, but it takes a few hours to warm the room up. We just use an oil heater to keep it warm at night - two of them on really cold nights like last night.

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jonathan18

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#1586915 6-Jul-2016 08:43

We tried the heatpump in the hallway method to heat half of the house (aimed at the four bedrooms off the hallway), but it was always bound to fail. This was a high-wall model, and I think that in itself was a mistake. But more substantially I think there's a flaw in the idea of heating one space and expecting the heat to be pushed into other rooms off this space, especially given the primary heating space (the hallway) is essentially only a transitory space.

We replaced this with a ducted system, that has ducts in all bedrooms as well as the rest of the house (bedrooms and hall are in a zone of their own), and I wished I'd done this from day one.

I agree that it's overkill putting separate units in each bedroom (I'm sure Consumer has been commenting recently that the ROI when putting heatpumps in small spaces means it's more cost-effective to use a more conventional/cheaper heating source). I also think ducted systems are less dominant aesthetically and quieter (just a duct in ceiling or floor).

So, yep, ducted systems may have a higher cost, but the convenience of being able to easily (and automatically) heat the whole house cannot be overstated! It's also been surprisingly cheap to run - our weekly power bills have increased by $15-20 a week over the pre-winter cost, from around $20 - that's running it for a minimum of 2.5 hours in the morning and probably a similar period of time in the afternoon, plus much of the weekend.

chimera

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#1587053 6-Jul-2016 12:30

jonathan18:

We tried the heatpump in the hallway method to heat half of the house (aimed at the four bedrooms off the hallway), but it was always bound to fail. This was a high-wall model, and I think that in itself was a mistake. But more substantially I think there's a flaw in the idea of heating one space and expecting the heat to be pushed into other rooms off this space, especially given the primary heating space (the hallway) is essentially only a transitory space.

We replaced this with a ducted system, that has ducts in all bedrooms as well as the rest of the house (bedrooms and hall are in a zone of their own), and I wished I'd done this from day one.

I agree that it's overkill putting separate units in each bedroom (I'm sure Consumer has been commenting recently that the ROI when putting heatpumps in small spaces means it's more cost-effective to use a more conventional/cheaper heating source). I also think ducted systems are less dominant aesthetically and quieter (just a duct in ceiling or floor).

So, yep, ducted systems may have a higher cost, but the convenience of being able to easily (and automatically) heat the whole house cannot be overstated! It's also been surprisingly cheap to run - our weekly power bills have increased by $15-20 a week over the pre-winter cost, from around $20 - that's running it for a minimum of 2.5 hours in the morning and probably a similar period of time in the afternoon, plus much of the weekend.

Cheers, yeah ducted makes sense. But a floor mounted model I think, at least based on the layout at the end of our hallway, would certainly work. It was still $2k though. That covers a lot of nightly oil heater running costs over a long period. I've asked a mate who installs joinery to get me a price on double glazing the kids rooms instead. Obviously not a method of heating, but better heat retention may just be enough to take the chill off. It certainly helped doing double glazing on a large window in our stair well. Think I'll stick to oil heater for the time being as we're in the process of putting a pool in ready for summer so that in itself is a v. large expense!

timmmay

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#1587058 6-Jul-2016 12:40

chimera:

Cheers, yeah ducted makes sense. But a floor mounted model I think, at least based on the layout at the end of our hallway, would certainly work. It was still $2k though. That covers a lot of nightly oil heater running costs over a long period. I've asked a mate who installs joinery to get me a price on double glazing the kids rooms instead. Obviously not a method of heating, but better heat retention may just be enough to take the chill off. It certainly helped doing double glazing on a large window in our stair well. Think I'll stick to oil heater for the time being as we're in the process of putting a pool in ready for summer so that in itself is a v. large expense!

PVC double glazed windows just cost me around $1600 each installed (ish), using the existing wooden frame and an "insert" method. Replacing the frame costs around $500 more and more time painting.

chimera

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#1587092 6-Jul-2016 13:19

timmmay:

chimera:

Cheers, yeah ducted makes sense. But a floor mounted model I think, at least based on the layout at the end of our hallway, would certainly work. It was still $2k though. That covers a lot of nightly oil heater running costs over a long period. I've asked a mate who installs joinery to get me a price on double glazing the kids rooms instead. Obviously not a method of heating, but better heat retention may just be enough to take the chill off. It certainly helped doing double glazing on a large window in our stair well. Think I'll stick to oil heater for the time being as we're in the process of putting a pool in ready for summer so that in itself is a v. large expense!

PVC double glazed windows just cost me around $1600 each installed (ish), using the existing wooden frame and an "insert" method. Replacing the frame costs around $500 more and more time painting.

Size of window? Got mates rates on mine, about 1200mm high by 2100mm wide for less than half that installed (aluminium, so likely less labour than timber)

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