heat pump running costs and noise

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#643226 19-Jun-2012 14:58

Jaxson: Also, the 3 times better than a standard electrical heater is only relevant during the optimum operating conditions, namely when your desired internal set point is very close to the ambient temperature outside.

ie You would expect 300% efficiency during periods where it's 20 degrees C outside and you want the room to be 21 degrees inside. The efficiency drops as the differential temperature gap increases. Simply, it won't be 300% efficient when it's 1 degree outside and you still want the temperature inside to be 21 degrees.

Flued Gas heaters are roughly 80% efficient at all times and temperatures. Gas costs roughly 1/3rd the cost of electricity so can work out cheaper during cold periods where the heat pump is not operating as efficiently.

Gas heaters don't cool so well though. Heat pumps can dehumidify, but only in cooling modes, which you don't tend to use so much when it's cold.

Pros and cons to everything.

+1 and modern wood burners are pretty efficient as well, as long as you have a ready (and sustainable) supply of wood.

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#643242 19-Jun-2012 15:17

If I recall correctly the standard heating COP is measured when the outdoor temp is 7C and the indoor is 20C. If it is colder than this outside or warmer than this inside (or a combination of the two) the COP will be lower.

We have a couple of the small Fujitsu units (3.4 kW heat 0.7 kW electrical). They are quiet unless they are working hard (generally the first 20 mins that they switched on if the indoor temp is low). The neighbours have just installed a new panasonic and at times when we are inside we can hear their outdoor unit even though our heat pumps are also on. I wouldn't call it loud, but definitely audible.

For a 700W unit at full output you would be looking at around $30/week assuming 25 c/kwh. Like others have said the unit shouldn't be going flat tack all the time though. Our winter power bill is around $200, but we have a small house (<100 square metres) and it is relatively well insulated. Summer is around $100, so I guess our two heat pumps are using about $25/week combined.

NonprayingMantis

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#643249 19-Jun-2012 15:26

My understanding is that if you have reticulated gas already connected to your house, then gas ducted heating is probably the best option for you.
Running costs are roughly the same as a heatpump (swings and roundabouts, but largely averages out)

Whilst the install is generally more expensive (5k-8k for gas ducted heating vs 2-3k for heatpump), you do get to heat the whole house for that amount, rather than one room.
Also, you won?t need a DVS or HRV either, which will save you 1-2k on that too.

NonprayingMantis

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#643250 19-Jun-2012 15:26

jonherries:
Jaxson: Also, the 3 times better than a standard electrical heater is only relevant during the optimum operating conditions, namely when your desired internal set point is very close to the ambient temperature outside.

ie You would expect 300% efficiency during periods where it's 20 degrees C outside and you want the room to be 21 degrees inside. The efficiency drops as the differential temperature gap increases. Simply, it won't be 300% efficient when it's 1 degree outside and you still want the temperature inside to be 21 degrees.

Flued Gas heaters are roughly 80% efficient at all times and temperatures. Gas costs roughly 1/3rd the cost of electricity so can work out cheaper during cold periods where the heat pump is not operating as efficiently.

Gas heaters don't cool so well though. Heat pumps can dehumidify, but only in cooling modes, which you don't tend to use so much when it's cold.

Pros and cons to everything.

+1 and modern wood burners are pretty efficient as well, as long as you have a ready (and sustainable) supply of wood.

Jon

oh come on, it's not like it grows on trees you know!

mxpress

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#643252 19-Jun-2012 15:29

heavyusr: Well my place does not have a heat pump but I want to get one installed

If I leave it on the entire day for 1 week what would you estimate the cost to be?

I have been searching youtube for the noise the outdoor unit of the heat pump makes but all the videos are of defective outdoor units. Could someone record their outdoor heat pump unit for 20 seconds and upload the video so I can hear how loud the noise is?

Whatever you do, DON'T install the outside unit on the wall. A cheap install but the noise is terrible. Always have it on the ground and noise won't be an issue at all (unless you buy a 'cheap' unit like what the warehouse sell.

mxpress

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#643258 19-Jun-2012 15:35

Jaxson: Heat pumps can dehumidify, but only in cooling modes, which you don't tend to use so much when it's cold.

This interests me. I had always believed that heat pumps would be an effective way of tackling household dampness in winter, but I guess a ventilation system or portable dehumidifier is also a must?

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Jaxson

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#643259 19-Jun-2012 15:35

I know of one case where a new house application had a note on the consent that the selected heat pump model could exceed allowable noise levels for that residential zone....

As above though, pro's and con's for everything. We currently have a flued gas econosaver heater in the lounge, mainly because it was substantially cheaper to buy and connect given we were replacing an existing gas heater in the same position. No cooling, but all the benefits of time scheduling to come on in the morning and pre heat the room etc.

Purchased 2nd hand off trademe from someone who went to air con or gas central heating, one of the two. You can get great deals on 2nd hand gas units right now as people are moving with the air con craze. By contrast, 2nd hand air con units are possibly being removed for a not so genuine reason....

Jaxson

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#643260 19-Jun-2012 15:40

alasta:
Jaxson: Heat pumps can dehumidify, but only in cooling modes, which you don't tend to use so much when it's cold.

This interests me. I had always believed that heat pumps would be an effective way of tackling household dampness in winter, but I guess a ventilation system or portable dehumidifier is also a must?

Basically you remove the moisture by passing warm moist air over colder pipes, where it condenses and drains away. To achieve this you need cold pipes, which you don't tend to get in winter. Dehumidifying modes switch to cooling for a short period (which cools the room too) and then back to warm again, which costs you money as you've just cooled the air you previously paid to heat.

So, they can do it, just it costs you more to run is all. Still worth doing though, as dryer air costs less to heat. Pros and cons again!

Yes, air con units are just fan heaters on the wall. They don't bring in fresh air or remove stale air unless you have a specially ducted ventilation system component, which typically costs more. If you want fresh air, or to reduce CO2 levels, then you need to ventilate, either forced via fan supply, or passively by opening the windows/doors and allowing some draught through.

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#643261 19-Jun-2012 15:46

alasta:
Jaxson: Heat pumps can dehumidify, but only in cooling modes, which you don't tend to use so much when it's cold.

This interests me. I had always believed that heat pumps would be an effective way of tackling household dampness in winter, but I guess a ventilation system or portable dehumidifier is also a must?

I don't quite agree with this. One of the basic principals of refrigeration is that a heat pump running in warming mode will reduce the humidity as the temperature increases above the dew point. It's not acting as a dehumidifier / air conditioner per se while in heating mode, but the warm air will be dry(er) air. Warm and cold air both have different characteristics when it comes to holding moisture.

NonprayingMantis

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#643270 19-Jun-2012 16:14

Jaxson: I know of one case where a new house application had a note on the consent that the selected heat pump model could exceed allowable noise levels for that residential zone....

As above though, pro's and con's for everything. We currently have a flued gas econosaver heater in the lounge, mainly because it was substantially cheaper to buy and connect given we were replacing an existing gas heater in the same position. No cooling, but all the benefits of time scheduling to come on in the morning and pre heat the room etc.

Purchased 2nd hand off trademe from someone who went to air con or gas central heating, one of the two. You can get great deals on 2nd hand gas units right now as people are moving with the air con craze. By contrast, 2nd hand air con units are possibly being removed for a not so genuine reason....

That sounds rather dangerous. I would never buy a second hand gas heater.

bazzer

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#643271 19-Jun-2012 16:20

sbiddle:
alasta:
Jaxson: Heat pumps can dehumidify, but only in cooling modes, which you don't tend to use so much when it's cold.

This interests me. I had always believed that heat pumps would be an effective way of tackling household dampness in winter, but I guess a ventilation system or portable dehumidifier is also a must?

I don't quite agree with this. One of the basic principals of refrigeration is that a heat pump running in warming mode will reduce the humidity as the temperature increases above the dew point. It's not acting as a dehumidifier / air conditioner per se while in heating mode, but the warm air will be dry(er) air. Warm and cold air both have different characteristics when it comes to holding moisture.

Where is the water going?

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minimoke

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#643272 19-Jun-2012 16:25

I've got two heat pumps heating around 240 SQM. Basement remains unheated and I'll put a third in there one day. Don’t recall the brand – Panasonic or Fujitsu or something.

Costs - no idea really. I'm a bit slack on power. Its a bit like petrol - I need it so I pay it. I guess the power bill goes up around $200 - $250 a month in winter. It fluctuates depending on how much the pumps get used. June will get a flogging because we had snow on the ground, schools closed so everyone at home for days then followed by -5 frosts where the ice didn't melt all day Heat pumps are on continuously (but are inverters so they do cycle) over the weekend and upstairs is on every night throughout the week to keep bedrooms warm. Had a crap summer (again) so the air con didn't get used so no additional cost in summer.

Noise of outside units a bit irrelevant unless you are worried about the neighbours. Check the units specs and see what the outside unit dB is and compare with other units. They do make a noise and I wouldn’t' want one outside my bedroom window. Isolating by putting on the ground, rather than the wall will help – but not totally

Its the noise of the inside units you really want to watch. Our lounge one is dead silent with background ambient noise. Upstairs is a gentle drone and no way does it interrupt sleep. Only thing is on the real cold nights it tends to snap and crackle a bit as something is dealing with the ultra cold outside temperature. Probably got to be -5 or more below before it does this.

Its a good all round heat – but not as good as in slab I had in a previous house.

Also build in cost of servicing. Ours are done once a year for around $100. I clean the filters out once a month or so - amazing what they suck up! I still reckon there’s silt in the air!

Handle9

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#643277 19-Jun-2012 16:33

bazzer:
sbiddle:
alasta:
Jaxson: Heat pumps can dehumidify, but only in cooling modes, which you don't tend to use so much when it's cold.

This interests me. I had always believed that heat pumps would be an effective way of tackling household dampness in winter, but I guess a ventilation system or portable dehumidifier is also a must?

I don't quite agree with this. One of the basic principals of refrigeration is that a heat pump running in warming mode will reduce the humidity as the temperature increases above the dew point. It's not acting as a dehumidifier / air conditioner per se while in heating mode, but the warm air will be dry(er) air. Warm and cold air both have different characteristics when it comes to holding moisture.

Where is the water going?

It's still there but the capacity of air to hold water changes as it heats up. This is expressed in terms of absolute humidity and relative humidity. For the same absolute humidity (grams water/kg of air) the relative humidity (%) is different at different air temperatures.

e.g at 30 degrees Celsius 100% rH(i.e. when condensation occurs) is approx 27g H2O/kg of air
at 20 degrees Celsius 100% rH is approx 15g H2O/kg of air.

minimoke

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#643289 19-Jun-2012 16:47

Handle9:
bazzer:
sbiddle:
alasta:
Jaxson: Heat pumps can dehumidify, but only in cooling modes, which you don't tend to use so much when it's cold.

This interests me. I had always believed that heat pumps would be an effective way of tackling household dampness in winter, but I guess a ventilation system or portable dehumidifier is also a must?

I don't quite agree with this. One of the basic principals of refrigeration is that a heat pump running in warming mode will reduce the humidity as the temperature increases above the dew point. It's not acting as a dehumidifier / air conditioner per se while in heating mode, but the warm air will be dry(er) air. Warm and cold air both have different characteristics when it comes to holding moisture.

Where is the water going?

It's still there but the capacity of air to hold water changes as it heats up. This is expressed in terms of absolute humidity and relative humidity. For the same absolute humidity (grams water/kg of air) the relative humidity (%) is different at different air temperatures.

e.g at 30 degrees Celsius 100% rH(i.e. when condensation occurs) is approx 27g H2O/kg of air
at 20 degrees Celsius 100% rH is approx 15g H2O/kg of air.

Basically heat pumps do not get rid of condensation in winter - we still need to mop it off the window sills

mxpress

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#643320 19-Jun-2012 17:49

minimoke:
Handle9:
bazzer:
sbiddle:
alasta:
Jaxson: Heat pumps can dehumidify, but only in cooling modes, which you don't tend to use so much when it's cold.

This interests me. I had always believed that heat pumps would be an effective way of tackling household dampness in winter, but I guess a ventilation system or portable dehumidifier is also a must?

I don't quite agree with this. One of the basic principals of refrigeration is that a heat pump running in warming mode will reduce the humidity as the temperature increases above the dew point. It's not acting as a dehumidifier / air conditioner per se while in heating mode, but the warm air will be dry(er) air. Warm and cold air both have different characteristics when it comes to holding moisture.

Where is the water going?

It's still there but the capacity of air to hold water changes as it heats up. This is expressed in terms of absolute humidity and relative humidity. For the same absolute humidity (grams water/kg of air) the relative humidity (%) is different at different air temperatures.

e.g at 30 degrees Celsius 100% rH(i.e. when condensation occurs) is approx 27g H2O/kg of air
at 20 degrees Celsius 100% rH is approx 15g H2O/kg of air.

Basically heat pumps do not get rid of condensation in winter - we still need to mop it off the window sills

WE use heat pumps and homevent system. Perfect. No more condensation in this 70 year old freezing cold home.

mxpress

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