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  Reply # 643359 19-Jun-2012 18:35 Send private message

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.


Warmer air can hold more water.
How is that heat pump specific?

As Bazzer says, you haven't removed any water from the house, just heated the air so it can hold more.

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  Reply # 643376 19-Jun-2012 18:55 Send private message

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


At the end of summer I bought a Mitsubishi Electric dehumidifier which I'm really impressed with. When I get condensation in the morning I just put the dehumidifier in front of the window with the louvre set towards the window and it seems to deal to it pretty well.

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  Reply # 643382 19-Jun-2012 19:06 Send private message

Not meaning to labour the point but insulation is the first best option which most people don't consider. You can add a lot of insulation for the cost (and ongoing cost) of heating.

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  Reply # 643391 19-Jun-2012 19:27 Send private message

Jaxson:

Warmer air can hold more water.
How is that heat pump specific?

As Bazzer says, you haven't removed any water from the house, just heated the air so it can hold more.


It's relevant when you are controlling for comfort but not at all heat pump specific. Warm air can hold more water so feels less 'damp'. If you have good insulation (including curtains that insulate the windows or double glazing) and the house is warm then you get less condensation. It's the same reason that people  put in insulation and get less condensation. There's the same absolute amount of water in the house, it's just that it never gets to dew point so it doesn't condensate or feel damp.

If you're controlling ventilation as well (i.e. supply air fan , return air fan and damper, outside air damper, mixed air damper) you often will do an enthalpy calculation which takes into account the humidity of the space and the outside air to achieve better comfort and much better energy efficiency. You DON'T do this on houses though - it costs too much.

Once again not heat pump specific but it is relevant.

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  Reply # 643395 19-Jun-2012 19:35 Send private message

Handle9:

Once again not heat pump specific but it is relevant.


Thanks, not disagreeing with you Smile

I was just explaining the method by which water is physically removed/extracted from the air by a heat pump.

Agreed with the other statements, as in you'd want to find out where your current heat is going (draughts/lack of insulation) and water is coming from (lack of ventilation/water vapor extraction fans/moist underfloor) first.

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  Reply # 643398 19-Jun-2012 19:41 Send private message

Jaxson:
Handle9:

Once again not heat pump specific but it is relevant.


Thanks, not disagreeing with you Smile

I was just explaining the method by which water is physically removed/extracted from the air by a heat pump.

Agreed with the other statements, as in you'd want to find out where your current heat is going (draughts/lack of insulation) and water is coming from (lack of ventilation/water vapor extraction fans/moist underfloor) first.


Yeah at the end of the day a heat pump is just a means of heating and cooling - it doesn't have any mystical qualities beyond that. You can do everything a heat pump does another way but they are relatively cheap and efficient. 

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  Reply # 643414 19-Jun-2012 20:11 Send private message

nakedmolerat:
johnr: New Panasonic head pump installed last week and it's super quiet


i havent heard of 'head' pump yet.. is this a new type? 


johnr puts out so much hot air, they made a special model for him.  its super cheap to run too :P




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  Reply # 643416 19-Jun-2012 20:22 Send private message

Jaxson:

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....


i put central gas in my house a couple of years ago,  at the time i was looking at:

$5,000 for a flued gas heater (new, not 2nd hand), $9,000 for two heaters plus some heat transfer systems
$4,000 for a single heat pump
$18,000 for heat pump driven central heating
$8,000 for gas driven central heating (brivis)

we already had reticulated gas for hot water and cooking

for what we wanted, the brivis gas central heating system was by far the best value.  we didnt need any cooling - in fact specifically didnt want it - so that never really featured in the decision making process.  also, at 6c per kW, the gas was roughly 1/4 of the price per kW of electricity so there wasnt really that much difference in operating costs.  In fact, gas is still around 6c per kW now and electricity has gone up a bunch so the gas is easily cheaper now.

the problem with including a cooling solution is that you end up using it full time in the summer, and your 'high winter heating bills' suddenly become a year round problem....




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  Reply # 643419 19-Jun-2012 20:25 Send private message

jonherries: Not meaning to labour the point but insulation is the first best option which most people don't consider. You can add a lot of insulation for the cost (and ongoing cost) of heating.


and before i did my central heating i insulated the entire house as best as i could.  ceiling topup and underfloor.  ambient temp in the house increased from 8degC-12decC to around 16degC-18degC without any heating going.




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  Reply # 643582 20-Jun-2012 08:44 Send private message

Regs:
Jaxson:

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....


i put central gas in my house a couple of years ago,  at the time i was looking at:

$5,000 for a flued gas heater (new, not 2nd hand), $9,000 for two heaters plus some heat transfer systems
$4,000 for a single heat pump
$18,000 for heat pump driven central heating
$8,000 for gas driven central heating (brivis)

we already had reticulated gas for hot water and cooking

for what we wanted, the brivis gas central heating system was by far the best value.  we didnt need any cooling - in fact specifically didnt want it - so that never really featured in the decision making process.  also, at 6c per kW, the gas was roughly 1/4 of the price per kW of electricity so there wasnt really that much difference in operating costs.  In fact, gas is still around 6c per kW now and electricity has gone up a bunch so the gas is easily cheaper now.

the problem with including a cooling solution is that you end up using it full time in the summer, and your 'high winter heating bills' suddenly become a year round problem....


we have had ducted gas heating installed recently for only $5k.   6 vents.

got it from these guys:http://www.greengas.co.nz/

terrible website, but very good service.

heats the house (160sqm) in only about 10-15 mins

and yes, gas is still very cheap.

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  Reply # 643614 20-Jun-2012 09:30 Send private message

I have two heat pumps, a 3-4 year old Daikin and a 3 month old Fujitsu Nocria. The outdoor units for both are so quiet you often have to put your ear up to them to see if they're working. Sometimes I can hear them operating in the middle of the night, if there's no noise around. Outdoor unit noise is irrelevant IMHO.

Indoor unit noise is more of an issue. I have the largest Nocria and indoor on high power it sounds like a hurricane, but I think it could heat a huge space. On "super quiet" it's still not particularly quiet, you have to turn the TV up a notch to compensate for it being on. It's not too bad, but if you want a heat pump you don't hear, don't get a large nocria. The Daikin's a little quieter. I'm talking about when the room is more or less up to heat, as they're all loud if it's really cold and they're working hard.

The Nocria we got is about 30-40% more powerful than the Daikin. It heats better, it spends less time on, and it seems to use less power. That's expected with a larger, newer unit.

If I was just starting to do heat pumps now I'd get a central heating unit. Fujitsu does one called the "sleep pump" which I think is reasonably priced, it has three outputs so you can heat three rooms easily. No doubt you can get larger ones.

Re costs. We have three people in an old three bedroom house in Wellington. I keep the house warm, around 21 degrees between 5pm and 11pm, I leave it on overnight if it's really cold, going off around 7am. On weekends we often don't turn it off. We only heat the living area (lounge, bedrooms, bathroom) weekdays, weekend we heat the whole house. It's a pretty old house but I've done a lot of insulation work, wall, under floor, and ceiling, though old houses never hold the heat as well as new houses no matter how much insulation you put in. Our summer power bill is around $150, winter it's $200 - $250, maybe a little more when it's really cold. Before I had insulation or a heat pump the bill got up to $450 some months in winter, and the house was incredibly cold. Insulation is essential, heat pumps are great though.

alasta:  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?


In my opinion, it's not. They use power to do it, and they're only mildly effective in my experience.

alasta:

At the end of summer I bought a Mitsubishi Electric dehumidifier which I'm really impressed with. When I get condensation in the morning I just put the dehumidifier in front of the window with the louvre set towards the window and it seems to deal to it pretty well.


A cheaper, quicker option is to wipe the window with a microfibre cloth, hang it outside or in a well ventilated room, and open the window. You're using a lot of power to do the same thing.


My house used to be damp, with bad condensation. They're separate problems and I dealt with them separately. The dampness was fixed by putting in a plastic sheet on the ground under the house, properly staked down, taped around the piles, etc. You have to be through, best get a professional to do it. I had underfloor insulation put in at the same time, which no doubt helps. I also had my driveway redone, during that I put in a lot of drainage to stop water going under the house.

Condensation I dealt with by putting in retrofit double glazing. It cost me about $4K for four rooms onto wooden windows, and works well. I read in consumer that it's around 80% as effective as proper double glazing at around 20% the price. I've gone from having a puddle on my window sills that you could splash in and very wet windows every day to having a light mist on cold days. Aluminum windows are a bit harder to do I think, the aluminum conducts heat in.

I also have a cheap ventilation system in my house that the previous owner put in, I have it on a timer running 10am to 4pm in winter, and early morning and late evening in summer. One day I'll replace it with a heat recovery ventilation system, one that uses the outgoing warm damp stale air to preheat incoming air.

If I was putting heating or ventilation into a new house I would absolutely avoid downlights or cutting and hole in the ceiling. Any hole is a huge waste of heat, even a small hole lets a lot of heat out. Vents for air or heat can be in the walls or floor, and if necessary can be piped down through the walls while they're being built.




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  Reply # 643616 20-Jun-2012 09:32 Send private message

NonprayingMantis:
Regs:
Jaxson:

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....


i put central gas in my house a couple of years ago,  at the time i was looking at:

$5,000 for a flued gas heater (new, not 2nd hand), $9,000 for two heaters plus some heat transfer systems
$4,000 for a single heat pump
$18,000 for heat pump driven central heating
$8,000 for gas driven central heating (brivis)

we already had reticulated gas for hot water and cooking

for what we wanted, the brivis gas central heating system was by far the best value.  we didnt need any cooling - in fact specifically didnt want it - so that never really featured in the decision making process.  also, at 6c per kW, the gas was roughly 1/4 of the price per kW of electricity so there wasnt really that much difference in operating costs.  In fact, gas is still around 6c per kW now and electricity has gone up a bunch so the gas is easily cheaper now.

the problem with including a cooling solution is that you end up using it full time in the summer, and your 'high winter heating bills' suddenly become a year round problem....


we have had ducted gas heating installed recently for only $5k.   6 vents.

got it from these guys:http://www.greengas.co.nz/

terrible website, but very good service.

heats the house (160sqm) in only about 10-15 mins

and yes, gas is still very cheap.


Terrible isn't the half of that site, although it does have a good slogan "from main to flame"

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  Reply # 643645 20-Jun-2012 10:09 Send private message

timmmay:
alasta:  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?


In my opinion, it's not. They use power to do it, and they're only mildly effective in my experience.

alasta:

At the end of summer I bought a Mitsubishi Electric dehumidifier which I'm really impressed with. When I get condensation in the morning I just put the dehumidifier in front of the window with the louvre set towards the window and it seems to deal to it pretty well.


A cheaper, quicker option is to wipe the window with a microfibre cloth, hang it outside or in a well ventilated room, and open the window. You're using a lot of power to do the same thing.


It sounds like you've done a lot of really effective stuff in your house, but the reality is that when you're renting and/or on a tight budget then you're stuck with temporary solutions. Unfortunately most landlords are in the business for a quick buck and won't spend any more than they absolutely have to on their properties.

A portable dehumidifier might not be the best solution to dampness problems, but if it's too cold to open windows and you don't have the opportunity to make significant improvements to the house then it's much better than nothing.

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  Reply # 643646 20-Jun-2012 10:14 Send private message

Ah yes, rental properties are different. Still, wiping the windows down with a cloth will reduce the power usage of the dehumidifier.

I open the windows during the day to get rid of all the moisture people make (breathing, showering), then heat it up at night. Damp houses are much more difficult to heat than dry houses.




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  Reply # 643746 20-Jun-2012 12:57 Send private message

dehumidifiers are great - you get the useful heat from them as well. If I leave a dehumidifier on in the bathroom then its not too cold, and quite dry by the morning. Leave the extractor fan on and its still damp and an icebox instead. Same for the kitchen. Make quite a viable alternative to a small useless heater.




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