Ducted heatpump advice sought

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#1342584 13-Jul-2015 21:19

bfginger: I'd sort out the wall insulation and double glazing before installing a ducted heat pimp. Ceiling and underfloor are half of the heat loss but heat will still be streaming through those windows and walls. Many underfloor and older ceiling insulation installations are ineffective too. If you read this forum often you'll know standard NZ windows joinery is poor quality and won't be much of an improvement over old wooden single glazed windows.

An installer will want to install a bigger system than what would be necessary if it was fully insulated. 16kW is big and most 1920s houses are modestly sized.

Some ducted heat pump systems aren't very efficient so look at the coefficient of performance (COP) rating in the model specifications.

Perhaps this would make sense if we were wealthy (and if this was true we'd be building a new house!), but I'd be amazed if you can demonstrate it would be cost-effective for us to insulate the walls (probably requiring the re-gibbing of every room, as I wouldn't touch the foam stuff we had put in our last house) and have the windows double-glazed. I can't cope with modern window frames in an old house, whether or not such new frames are more efficient. The alternative is that which my brother looked at having done to the windows in his early 1900s house (ie existing frames rebated etc), and the cost was prohibitive enough for him to give up on the idea. I'd imagine it'll be the same for our house.

As such, I'm satisfied we've done the most practical and affordable attempts to improve insulation, and therefore are happy that heating's where it's at for our situation.

The COP of the model we're looking at is 3.96, which seems within the acceptable range for ducted systems?

jonathan18

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#1342597 13-Jul-2015 21:25

dgashby: We have a similar setup and are pretty happy with it. It has struggled a bit the last couple of mornings when we've had -6 degree frosts and the efficiency has probably suffered as the outside unit spends time defrosting. We have other heating options as well in case of power cuts, but the ducted system is great at getting the entire house warm.

One thing we would change is in our kids bedrooms. Each bedroom has an outlet, but the intake for that end of the house is in a hallway. The problem is if you close their bedroom doors at night the airflow can't circulate from the outlet back to the intake and the rooms quickly overheat. The obvious solution is to leave the doors slightly ajar but kids will sometimes find the tiniest excuse for climbing out of bed, and if you're running the heatpump on a timed cycle then the rooms cool down much faster once the heatpump shuts off if the doors are ajar. Currently we have the heatpump programmed to come on twice for an hour each night. I've got an Arduino with a temperature sensor logging the temperature at cot level in our youngest's bedroom to Xively every 60 seconds and review this every now and then to see if we need to adjust the programme.

Thanks for the really useful post. We're in exactly the same position with the kids' bedrooms being shut at night. One of the installers commented today on this being a potential issue, so interesting to see how you manage it. I'm wondering if we can get into a habit of opening their doors a bit after they've gone to sleep (or get them to the point they can go to sleep with them open!) just to ensure the flow back to the return is maintained, but also could try the other option of having it turn on occasionally over the night.

Whereabouts do you live, and what brand have you guys got installed?

Jase2985

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#1342620 13-Jul-2015 22:10

Could try trimming the bottoms of the doors by a cm or 2 to allow air flow, or failing that install vents in the door

dgashby

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#1342633 13-Jul-2015 22:20

We're in Mandeville, just north and inland from Christchurch. It was a new single story build, 400m2 to heat. Underfloor would have been just too expensive to run for that area. We went with 2 Fujitsu units, a 16kw unit for the main living areas (all open plan) and master bedroom, and an 8kw unit for the other end of the house which includes two kids rooms, a play area, and guest bedroom. The other advantage of the heat pump is we can cool in summer if it gets really hot. The internal fan on the 16kw unit does hum a bit when operating at full speed, the noise is most noticeable around one of the intakes but that away from the living areas so doesn't really bother us. The 8kw unit is barely noticeable. Having two units is also quite good in that we control the kids end separately from the rest of the house. The installer also installed a damper on the guest bedroom outlet so with the flick of a switch you can stop all flow into that room if you don't have any need to heat that room.

I'd ask your installer on his opinion about putting intakes in the kids rooms to provide for the return airflow. We never even thought of it at the time so didn't raise it. It probably wouldn't be too hard to modify if we really wanted too, probably just a matter of splitting of splitting the intake ducting up in the ceiling space and installing intake vents in each room The unit is located between their rooms so it wouldn't involve much ducting.

One other thing worth considering is access for maintenance. Our inside units were installed in the roof space before the ceiling was lined, if we ever had a major problem with it and needed to replace a ceiling unit I hate to think how they would do that without destroying the ceiling. That might not be such a problem for you as being an install into and existing house they are going to have to consider that right from the start.

This was the first time we've built and thought we had planned things out pretty carefully but there's always little details that you look back on and think I wish I'd done that slightly differently. Glad we can help with some of the practical stuff we've learn't along the way.

timtait

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#1342635 13-Jul-2015 22:26

dgashby: We're in Mandeville, just north and inland from Christchurch. It was a new single story build, 400m2 to heat. Underfloor would have been just too expensive to run for that area. We went with 2 Fujitsu units, a 16kw unit for the main living areas (all open plan) and master bedroom, and an 8kw unit for the other end of the house which includes two kids rooms, a play area, and guest bedroom. The other advantage of the heat pump is we can cool in summer if it gets really hot. The internal fan on the 16kw unit does hum a bit when operating at full speed, the noise is most noticeable around one of the intakes but that away from the living areas so doesn't really bother us. The 8kw unit is barely noticeable. Having two units is also quite good in that we control the kids end separately from the rest of the house. The installer also installed a damper on the guest bedroom outlet so with the flick of a switch you can stop all flow into that room if you don't have any need to heat that room.

I'd ask your installer on his opinion about putting intakes in the kids rooms to provide for the return airflow. We never even thought of it at the time so didn't raise it. It probably wouldn't be too hard to modify if we really wanted too, probably just a matter of splitting of splitting the intake ducting up in the ceiling space and installing intake vents in each room The unit is located between their rooms so it wouldn't involve much ducting.

One other thing worth considering is access for maintenance. Our inside units were installed in the roof space before the ceiling was lined, if we ever had a major problem with it and needed to replace a ceiling unit I hate to think how they would do that without destroying the ceiling. That might not be such a problem for you as being an install into and existing house they are going to have to consider that right from the start.

This was the first time we've built and thought we had planned things out pretty carefully but there's always little details that you look back on and think I wish I'd done that slightly differently. Glad we can help with some of the practical stuff we've learn't along the way.

If you don't mine me asking, how have your power bills been over winter with those big units?

dgashby

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#1342654 13-Jul-2015 22:47

I have considered vents in the door, we did similar in our offices at work. The aesthetics aren't great so it doesn't have a very high wife approval factor though :-)

Our power bills average around $300-$350 per month for June-Aug/Sep depending on weather of course. We get a fair bit of solar gain on a sunny day so although frosty mornings start chilly, the house quickly heats up once the sun is up. We're also on a trickle water supply so have a 20000L tank with a pump so whenever we turn on the tap we're using power. Hot water is via Rinnai gas heaters.

timtait

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#1342655 13-Jul-2015 22:49

dgashby: I have considered vents in the door, we did similar in our offices at work. The aesthetics aren't great so it doesn't have a very high wife approval factor though :-)

Our power bills average around $300-$350 per month for June-Aug/Sep depending on weather of course. We get a fair bit of solar gain on a sunny day so although frosty mornings start chilly, the house quickly heats up once the sun is up. We're also on a trickle water supply so have a 20000L tank with a pump so whenever we turn on the tap we're using power. Hot water is via Rinnai gas heaters.

Ah yeah that's not bad at all, thanks.

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jonathan18

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#1342922 14-Jul-2015 11:41

Can anyone offer advice regarding the best type of vents? I'm having two totally condradictory views from two installers regarding the use of the 'jet'-like vents. These apparently have a bi-metal feature that opens up those holes pointing directly down, so when the air reaches a certain temperature it is pushed down, but when the air is cooler it is expelled out the sides (much like the standard fittings). Edit: apparently they also have a switch to turn off the jet feature, in which case they operate all the time in the same manner as the standard vents.

The installer yesterday swore by these as the best way to ensure good distribution of heat, while the other one says they've created draft issues every time they've installed them. I just don't know who to believe on this, so does anyone have any thoughts on this? I totally agree that, should we go with these 'jet' ones, the positioning of them is critical (ie, never under where people sit/sleep).

Another key difference between the recommendations is one installer says we only need one 200mm vent in the kitchen/dining, whereas the other has allowed for two (as per diagram, which shows a 3.62kW need for that space, which is considerably higher than the other rooms, which seems logical to me given the larger space). Any thoughts as to which would be most appropriate?

Thanks again.

bfginger

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#1345835 16-Jul-2015 22:53

A ducted heat pump wasn't something I associated with those concerned about the price of insulation renovations. When heating rooms that are losing more heat there is more thermal layering which means lower air is colder than higher air. When the heat pump is having to blow more hot air it is less comfortable too. Once the heat pump is turned off the temperature will drop faster and further which means much higher peak relative humidity levels.

There are modern wooden windows that look like traditional frames but they would be more expensive than aluminium. uPVC in historic houses is controversial in the UK.

jonathan18

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#1345881 17-Jul-2015 06:19

bfginger:
A ducted heat pump wasn't something I associated with those concerned about the price of insulation renovations. When heating rooms that are losing more heat there is more thermal layering which means lower air is colder than higher air. When the heat pump is having to blow more hot air it is less comfortable too. Once the heat pump is turned off the temperature will drop faster and further which means much higher peak relative humidity levels.

There are modern wooden windows that look like traditional frames but they would be more expensive than aluminium. uPVC in historic houses is controversial in the UK.

Sorry?

Ok, let me walk it through for you.

We have a house which we would like to be warmer, throughout.

We have already completed the obvious and affordable elements of keeping it warm, namely ceiling and under-floor insulation, so to make it warmer we are aware the next step will be more costly.

But, given we are not wealthy, that next step will need to be a relatively affordable and cost-effective solution.

So, for $10-14,000 upfront and with some additional ongoing cost (given we already have the cost of heating the house with a mix of wood, gas and electric) we can achieve a beautifully warm house by installing a ducted heatpump.

Or, for - and I'm guessing here but I bet it's at least this much - we could spend $50-80,000 on ripping the gib off all internal walls, sticking in insulation, re-gibbing, plastering, and painting all of them; and either replace every single window with double glazed units or have all existing window retrofitted with double glazing, to achieve a significant improvement in warmth, and possibly still need some form of additional heating. And don't forget the hassle of doing this with a young family.

Chosing between these two seems like a pretty simple decision to me.

Of course I understand there are trade-offs here, including those you point out above. But then again I've been in houses of the same era with similar systems and I know how well they work relative to our house.

And in the end, we can afford one of these options, but not the other. We also aren't stupid enough to completely over-capitalise on the house, as we know we will move at some point in the future.

graemeh

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#1345947 17-Jul-2015 09:25

jonathan18: But, given we are not wealthy, that next step will need to be a relatively affordable and cost-effective solution.

So, for $10-14,000 upfront and with some additional ongoing cost (given we already have the cost of heating the house with a mix of wood, gas and electric) we can achieve a beautifully warm house by installing a ducted heatpump.

No need for double glazing, just put up some decent thermal curtains or blinds to cover the windows. If you have one or two windows you like to leave open at night for the wonderful views then you could double glaze those.

timmmay

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#1345977 17-Jul-2015 09:48

Wavy curtains should touch the ground and / or the ceiling, otherwise you end up making a wind tunnel and it doesn't help insulation. Otherwise make sure they're fitted tight to the window frame.

Quinny

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#1346099 17-Jul-2015 11:20

Had 3 stand alone Panasonic for about 8 years in old house. Never missed a beat and loved them.

Was convinced after earthquakes for new build to go with Daiken and over all I am happy. For new build I looked at ducted but did not like the lack of room by room control so went with a mutli unit (that idles down to a economical 2.5k which is where these can really chomp thru power) and 4 front end room units. I also had all fitted with some chip that then talks back to a master wall unit that can control all 4. Happy yes with 3 of the 4 units but the big one in combined kitcehn/dining/2nd lounge is a power guzzler and I just wont use it. Think its a 6/7kw. The others are 2 or 3kw.

I looked at cassettes in roof for the big area but apparently they are even less economical that wall units and ducted well I was very much I wanted the heat where the people are not somewhere else.

elv

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#1346195 17-Jul-2015 12:52

Daikin heatpumps work in low temperatures. Most of the ducted Daikin heatpumps are made in Australia. I don' know where the Panasonics are made. Even in PN you should be concerned about being able to be use in low temperatures. If you have a decent frost and outside freezes your house will be cold you will regret your decision if you didn't consider it. Heating should work when it is cold.

timmmay

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#1346211 17-Jul-2015 13:03

elv: Daikin heatpumps work in low temperatures. Most of the ducted Daikin heatpumps are made in Australia. I don' know where the Panasonics are made. Even in PN you should be concerned about being able to be use in low temperatures. If you have a decent frost and outside freezes your house will be cold you will regret your decision if you didn't consider it. Heating should work when it is cold.

I'm not sure this post is entirely accurate, I'd like to see it backed up with references. Cold isn't really a problem, but cold + moisture can be. Heat pumps can work better in the deep south where there's little moisture than up north where it's cold but damp.

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