Question about ducted heatpumps

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benmurphy66

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#827839 29-May-2013 16:21

DarthKermit: A friend of mine has a heat pump in his lounge and a duct to suck the warm air from the lounge and into the hallway and one bedroom.

He said that it's very inefficient at transferring the heat from one place to the other.

From what I have read this isn't the best solution as the heat from the heat pump isn't hot enough to make it worthwhile. vs say a fire that will be something like 20+kw i.e. 50 degrees+ vs high 20s. (not an expert opinion just how I undestood it)

timmmay

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#827863 29-May-2013 16:46

I've read the same thing - no point doing heat transfer from a heat pump source. The air's about 50 degrees when it comes out of the heat pump, but moving 20 degree air around won't provide enough boost to the other room to be worthwhile.

A big fan in my hallway does help move air around on the odd occasion I need it though.

ajobbins

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#827897 29-May-2013 17:41

My ex-girlfriends uncle owned a company that did underfloor heating (both electrical and gas/water based). They had it installed in their house, which was a decent size but not huge.

I remember him telling me that his combined gas/electricity bill was usually between $600-1000 a month in winter. So I don't think they are particularly cheap to run!

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mattwnz

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#827917 29-May-2013 18:08

ajobbins: My ex-girlfriends uncle owned a company that did underfloor heating (both electrical and gas/water based). They had it installed in their house, which was a decent size but not huge.

I remember him telling me that his combined gas/electricity bill was usually between $600-1000 a month in winter. So I don't think they are particularly cheap to run!

That's why I wouldn't recommend doing it with that as the source of the heat, a normal water heater with electricity or gas will be costly. A heatpump water heater should be cheaper to run. You can also run them off a wetback on a woodburner, or even off a diesel boiler. But normal air heat pumps are pretty expensive to run. Not sure if there are octs comparisons, and different companies will tell you different things, as they are trying to sell you their product over others.

timmmay

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#827920 29-May-2013 18:10

If you do underfloor heating you really, really need to insulate under the concrete slab well. I'm not sure what the latest techniques are, but I've seen one where they do a concrete base, then insulation, then another slab that's built on. You insulate the sides as well. Heating the planet gets expensive.

I think NZ's well behind in energy efficient building techniques and technology.

mattwnz

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#827923 29-May-2013 18:21

timmmay: If you do underfloor heating you really, really need to insulate under the concrete slab well. I'm not sure what the latest techniques are, but I've seen one where they do a concrete base, then insulation, then another slab that's built on. You insulate the sides as well. Heating the planet gets expensive.

I think NZ's well behind in energy efficient building techniques and technology.

Your wou;dn't put in underfloor heating without insulation.
Insulation isn't difficult during construction, you basically put down a thick layer of EPS or XPS. XPS is probably better as it should have better insulation properties per thickness, so this is about 6cm thick. If using EPS, it probably needs to be closer to 10cm. Then you put your floor slab over the top of this. Insulating the sides is difficult, but you can lay a timber perimeter around the slab , inbetween the slab edge and the perimeter wall/footing edge, to isolate the two. You would still have your concrete footings around the perimeter which do go under the insulation layer, and confine the slab too. You can put insulation on the outside perimeter wall of the slab and footings, but it then has to be covered with something, and some councils do not like this. These days it is a good idea to insulate the slab anyway, even if you aren't putting in any underfloor heating.

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Snowflake

#828032 29-May-2013 21:48

benmurphy66:
joker97: is 13K worth the money? could you get say a gas central heating for that money?

Yeah I won't be paying that. it's pretty strange because of the three companies I have had review our heating requirements we have had three different pros & cons which all conflict with each other.

The GAS central heating came in at $9.5k. for a 8 outlet solution. that is without the costs of getting gas connected. Could use LPG bottles.

The Fujitsu ART45 with 8 outlets (4.2-16.2 kW) came in at $13,300.

Somebody else quoted a small Fujitsu ducted unit for $9,500.

I am just waiting on a quote for a split unit but I expect it to be similar money.

i got gas connected for free. because i'm in a 'rock' area, i had to dig my own trench from the meter location to the edge of the property to avoid paying anything. If i was somewhere else in auckland they would have done everything at no cost.

my gas central cost around $7.5k. Others, more recently, have also been looking at $8k. I have a brivis system, installers listed here: http://www.warmair.co.nz/gas-central-heating-outlets.html

My gas costs me around 6c per kWh plus a daily charge. My electricity costs me around 26c per kWh plus a daily charge. With a heatpump around 4x more efficient than gas, gas still wins at that price :)

Gas doesn't do cooling though - so if you need it, heatpump is only option. Not having cooling can save you $$$...

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#828033 29-May-2013 21:50

Oh, if i was building from scratch i would seriously look at in-slab water heating. Not sure of the cost comparisons though. Makes sense to insulate the slab as others have suggested.

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Linuxluver

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#828046 29-May-2013 22:35

joker97: is 13K worth the money? could you get say a gas central heating for that money?

Heat pumps cool as well as heat....so if the gas system only heats it's only doing half the job.

I just installed a heatpump in a flat I'm renting out and the ability to cool the place down on a hot summer day was a big component in that decision. The driveway outside heats up a LOT on a summer day...and the heat rises right into the open lounge windows. Closing the windows and running a heatpump to cool the place transforms the space from a potential sweatbox into a comfortable, sunny area year-round.

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#828057 29-May-2013 22:57

Oops i guess in dunedin there is never a need to cool lol ... And heatpump is warmish on a snowy day whereas a fire ... Giveth life!

graemeh

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#828217 30-May-2013 11:26

Don't worry about the gas running out any time soon. There is an over supply at the moment. One retailer hasn't increased their price in four years.

lapimate

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#829057 31-May-2013 21:56

mattwnz: ... how come you aren't looking at under slab underfloor heating? ...

I have observed that while under slab under floor heating makes for a nice warm floor/room on cold mornings, as a day warms up, particularly if there is solar warmth, the temperature can get uncomfortably high indeed. This is because a slab has so much thermal inertia and can be emitting heat long after the requirement has passed. Ordinary short-term thermostatic control does not help much with that problem.

Aredwood

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#830284 4-Jun-2013 00:15

Have seen the same problem in customers houses. Only use underfloor heating in areas with poor / no solar gain. Also most people using gas for underfloor heating skimp on the boiler they use. I have seen many installations using an infinity combined with a tempering valve to drop down the high temp from the infinity. It works but is inefficient. Best way is to use a European central heating boiler. Pick one that is Sedburk A rated. Problem is alot of them don't like NZ LPG. NZ natural gas is fine though.

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