Saving money using heat pump modes this summer?

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Forums › Finance and wealth management › Saving money using heat pump modes this summer?

TeaLeaf

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#243413 11-Dec-2018 08:36

Just a general query.

Ive got a semi new Fujitsu 6kw unit in my unit. It cools the whole house.

I was wondering, if I go out for the day, is it better energy wise to run it dehumidifier mode then turn the air on to 21 degrees when we have come home, as there is no humidity the air cools way quicker, vs turning the entire unit on and off?

I imagine the first but just wanted to check, to be honest the house max gets to 25 inside due to being very thick concrete and brick and tile. The only room that gets to 25 i one that has a skylight but not blind for it, 8 foot roofs in room and I think the kitchen and living room area is 10ft. It also has a skylight but the sun never passes directly through it to heat up the carpet etc.

Appreciate advice. Im use to Aus air con which is usually ducted in modern homes and in summer run 24/7. hence why so many brown outs and them having an energy issue. This is my first reverse cycle wall mounted heat pump.

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3885 posts

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#2143521 11-Dec-2018 17:51

Dehumidifier mode is just cooling mode with different fan control. Usually just slower fan speed, so the evaporator (indoor unit coils) get colder and more moisture condenses out from the air.

It will still use a similar amount of power compared to cooling mode. So definitely not cheaper to leave it running on dehumidifier mode while not at home.

Although experiment with using dehumidifier mode instead of cooling mode when you are at home and want cooling.

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Jase2985

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#2143581 11-Dec-2018 20:33

why not use the timer function? have it come on 30-60 mins before you get home?

Fred99

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#2143641 11-Dec-2018 21:31

Actually, if the warmest any room gets to is 25 deg C, why do anything at all?

blakamin

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#2143642 11-Dec-2018 21:39

Where in NZ are you? Some areas, cooling mode will add humidity to keep comfort levels.

Buy a Sensibo and set it to keep certain humidity and temp levels and let it do everything.

Aredwood

3885 posts

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#2143655 11-Dec-2018 22:26

blakamin:
Where in NZ are you? Some areas, cooling mode will add humidity to keep comfort levels.

Buy a Sensibo and set it to keep certain humidity and temp levels and let it do everything.

I have never seen a heatpump that also contains a humidifier (ignoring those standalone evaporative coolers, which are pretty much useless in NZ).

Reducing the air temperature of a room will cause the relative humidity to increase. But that is only because the relative humidity is a function of temperature.

blakamin

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#2143690 11-Dec-2018 22:41

Aredwood:
blakamin:

Where in NZ are you? Some areas, cooling mode will add humidity to keep comfort levels.

Buy a Sensibo and set it to keep certain humidity and temp levels and let it do everything.

I have never seen a heatpump that also contains a humidifier (ignoring those standalone evaporative coolers, which are pretty much useless in NZ).

Reducing the air temperature of a room will cause the relative humidity to increase. But that is only because the relative humidity is a function of temperature.

It's a good side effect then because my room sits on 22-24 degrees and 45-55% humidity whether outside is 29 (or 34) and 90%, or 44 and 10-20%.

Plus it doesn't add humidity at 34 and 90%, it takes it away, therefore it's maintaining a "comfort" level.

timmmay

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#2143747 12-Dec-2018 07:20

Heat loss is proportional to the difference in temperature. The longer the cooling is on the more it will cost.

If the air conditioner can effectively reach the whole house fairly quickly, I'd just turn it on with a timer 30-60 minutes before you need it cool. If, like my house, it takes quite a bit of time for the cooler air to get around corners turn it on a bit earlier.

In winter we do leave heating on when we're out, on low, but that's because the whole house feels warmer when it's kept warm all the time rather than heated just when we need it. It doesn't cost a lot more. Air condition doesn't seem to work the same way, maybe because sun in the windows can heat it up a lot, quickly.

SomeoneSomewhere

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#2144431 12-Dec-2018 19:03

Daikin makes the US7 which does have a humidifier, but these are very high end and uncommon.

Cooling increases *relative* humidity, because the air can hold less moisture when colder, so the same amount of moisture that was already in the air is now a higher percentage of the maximum possible moisture that could be suspended in the air. As such, lowering the temperature increases the RH value.

99.5% of heat pumps/aircon units have no way of actually adding water to the air.

TeaLeaf

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#2144463 12-Dec-2018 19:55

Im testing my pump with my dehumidifier and its 65% or below (when I turn it on) when the Air Con is on, I, not sure whether to use the Dry mode or not if you need moisture.

But 50-70% kills book lice and is unfriendly to mould spores, so Im happy if im In the Zone. Plus the house largely aside from one room gets a lot of sun.

Yes Tim, even though it points down the hall way, it doesnt naturally move right into the bedrooms. It has built in timer which Ill have to get my head around.

So what times lets say for Auck would you set the heat pump for? The thing is its sub 18 degrees at night and the morning, 18 being ideal sleeping temperature. And of course this all changes with the seasons.

I truely miss setting this on a master console and have it control the entire 3 story house via ducting lol, I also liked that I could control zones by not sending air to specific zones.

If this place meant more to me Id definitely go ducted.

In the mean time trying to live with what Ive got.

MadEngineer

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#2144534 12-Dec-2018 22:31

Unless you have a humidity problem, don’t unnecessarily dehumidify your house as it’s not good for your health. To answer your question about power saving, turn the heat pump on to your desired temperature and function when you’re at home to enjoy it and leave it alone. Get a thermometer for your bookshelf and place it at head height then set the heat pump at no more than a couple of degrees from the current room temperature. This works for us and we don’t have power bills over $150 /3 occupants.

The cooling function of an aircon will reduce humidity as a side effect as the air moisture condenses in the heat pump and gets drained outside.

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Aredwood

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#2144568 13-Dec-2018 01:27

There would be very few places in NZ where low humidity would be a problem. And lots of heatpumps actually struggle to remove humidity on cooling. As an easy way for a heatpump manufacturer to increase energy efficiency. Is to install a larger heat exchanger in the indoor unit. Less temp difference between the intake air and the refrigerant means better efficiency. But higher average heat exchanger temperature means less humidity will condense out. Although less humidity removed also reduces power consumption. Due to the latent heat of water.

I am currently modifying some approx 10 year old Mitsubishi Heavy Industries heatpumps that I have installed in my house. As they are not very good as dehumidifiers. Although they have quite good COP ratings despite their age.

MikeAqua

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#2144669 13-Dec-2018 10:09

I summer I use our heat pump in Off mode. Saves a lot of power.

Mike

Dairyxox

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#2144681 13-Dec-2018 10:15

Our heatpump has a fan mode which is quite good in summer.

Its not amazing at cooling but it pushes hot pockets out of the house, gets the air circulating, and has a cooling sensation across the skin.

timmmay

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#2144691 13-Dec-2018 10:33

MikeAqua:
I summer I use our heat pump in Off mode. Saves a lot of power.

It doesn't help much though. For example, in summer our kitchen / dining area can reach 35 degrees with blinds closed and windows on latch position, that's way too hot. Opening windows let's insects in. So we use air conditioning.

Jase2985

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#2144732 13-Dec-2018 12:00

timmmay:
MikeAqua:

I summer I use our heat pump in Off mode. Saves a lot of power.

It doesn't help much though. For example, in summer our kitchen / dining area can reach 35 degrees with blinds closed and windows on latch position, that's way too hot. Opening windows let's insects in. So we use air conditioning.

would it not be better to do something about the sun coming in to reduce the heat.

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