Ducted Heatpump help

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Klysznz

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#302428 22-Nov-2022 17:22

I've received two very different consultations and quotes for a ducted heatpump system, and keen for some advice.

Background:

1930 Bungalow in Auckland. House is North facing so eastside of house with bedrooms get morning sun. We have an existing highwall Heat pump in Master Bedroom, and an older (but working) HRV system. Ceiling, wall and underfloor insulation, but single glazed.

Previous owners used unflued Gas heaters during winter, which I'm not keen on using. This winter we used electric heaters, and only heated select rooms took forever and cost a lot to heat the kitchen.

Quote 1.

12.5Khw Ducted system (Daikin)
Retain Heatpump in Bedroom & HRV system (including the master bedroom would push us up to a 14Khw system)
Recommended no Zone (Not worth extra cost)

Quote 2.

16khw ducted system (Fujistsu) - consultant said I need 20Khw but with zoning 16khw should be enough
Fujitsu AnyWair Ducted Temperature Zone Control System
Fresh Air Duct + Positive Pressure Ventilation Integration
Will replace the heatpump in the bedroom and HRV system
Potentially would re-use HRV vent holes.

Really confused as the recommendations from the installers was completely different in term of total unit power and advice on Zoning.

Keen for thoughts/Advice

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#2999925 22-Nov-2022 17:27

There is a thread here on this topic, you're also only going to have opinions 3-5 added to the list.

You can work out the sizing yourself with online NZ calculators.

Zoning helps when you want rooms to be different temperatures.

E.g. living we had at 22 or so in winter, but bedrooms were closer to 17-18 so having two systems helped there.

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tweake

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#2999941 22-Nov-2022 18:58

what size house is it?

what size is the existing heat pump?

is that diagram of the duct outlet placements? some are in strange spots and surprised they need so many. one critical thing thats missing is the returns from each room. ie if you close the door how is the air flow going to get back to the main air return in the hallway. air flow in the room should go from air outlet to the return, the heating the room on the way. it won't heat much of the room if the outlet is close to the return or in the middle of the room.

i would ask them how they came up with the sizing. good chance you won't like the answer.

obviously the house has been reno'ed. but the big question is the floor. how well the heating works will depend on how air leaky the house is and the floor is often the major problem, unless its been sealed (check under the carpet areas).

its easiest, and possibly best, to keep the ventilation system completely separate. just leave it as is. integration gets complicated as you may see in other threads. big risk of them doing a hack job and making it worse.

timmmay

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#2999979 22-Nov-2022 20:34

Have a read of my ducted heat pump thread for some background.

If your rooms are the same temperature all day then you don't need zoned, but I suspect your bedrooms are warm in the morning, cooler in the afternoon, and your lounge / kitchen are warm in the afternoon. If that's true I would go with temperature controlled zones.

I agree with tweake about the diffuser locations - you really want them opposite the return. In your case you might get away with the red returns, plus maybe one in the entrance hall. Not sure why there would be two returns together. Returns in each room can be helpful, for example if you're trying to cool bedrooms at night it limits the cold air going to the rest of the house. I probably wouldn't do HRV integration, just stick it on a timer.

As for sizing, it depends on floor area, insulation, glazing, all kinds of things. 12kw for a whole house sounds a bit small to me, 16kw sounds more realistic.

Another thing to consider, if you cook strongly scented meals the smell will go into the other rooms. We have a separate system in the kitchen, mostly because it gets really hot, but I like not having the whole house smell like whatever we're eating. If you put a highwall in the kitchen 12kw might be enough for the rest of the house.

I like the idea that the control system is made by the heat pump manufacturer. They should be able to get better integration and control than 3rd party such as Airtouch. I'd look at reviews though to make sure it's ok. It'd also be good to have Home Assistant integration.

RunningMan

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#2999982 22-Nov-2022 20:38

Sorry for going a bit OT, but @timmmay do you have problems keeping a highwall unit clean in the kitchen?

timmmay

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#2999983 22-Nov-2022 20:39

RunningMan:

Sorry for going a bit OT, but @timmmay do you have problems keeping a highwall unit clean in the kitchen?

Nah it's fine. I clean it every six months or so, it's just a bit dusty like any other room. The extractor over the stove though gets quite oily and requires regular cleaning.

tweake

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#2999986 22-Nov-2022 20:58

timmmay:

I agree with tweake about the diffuser locations - you really want them opposite the return. In your case you might get away with the red returns, plus maybe one in the entrance hall. Not sure why there would be two returns together. Returns in each room can be helpful, for example if you're trying to cool bedrooms at night it limits the cold air going to the rest of the house. I probably wouldn't do HRV integration, just stick it on a timer.

there should ALWAYS be a return in each room that has a door. now that could be as simple as an under cut door, or a jumper over the door, or a direct return joining up to the others. otherwise when you close the door you get no airflow, therefore no heating/cooling and you pressurise the room and depressurise where the main returns are. that can also cause changes in flow in the other rooms.

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timmmay

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#3000037 22-Nov-2022 21:24

tweake:

there should ALWAYS be a return in each room that has a door. now that could be as simple as an under cut door, or a jumper over the door, or a direct return joining up to the others. otherwise when you close the door you get no airflow, therefore no heating/cooling and you pressurise the room and depressurise where the main returns are. that can also cause changes in flow in the other rooms.

Yes, of course, each room needs a return path for the air. In my place we have wall vents in the opposite corner from the diffusers near the floor, but per-room returns could be useful in some cases such as isolated rooms or preventing spill. The problem with ceiling mounted diffusers and returns is the air can skim across the top of the room causing stratification, so the diffusers need to be selected to push air down. My linked thread has some thoughts on that.

tweake

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#3000040 22-Nov-2022 21:27

i was half asleep and didn't see the room sizes. so you have about 105m2 room area. so a 16kw should be heaps, tho it will depend on site, house etc. your better to go undersized than oversized.

the other thing is return flow. main bedroom, lounge and office all return via the kitchen/dining room. (assuming those red squares are the return filters). your probably better to put one filter/return in the entrance hall or do a jumper from direct from lounge/main bedroom to main hallway. otherwise the kitchen will have 3/4 of the house air flow going through it, especially through that door way to the main hallway. not to mention the big jumper over the kitchen entrance hall door.

tweake

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#3000042 22-Nov-2022 21:29

timmmay:

The problem with ceiling mounted diffusers and returns is the air can skim across the top of the room causing stratification, so the diffusers need to be selected to push air down. My linked thread has some thoughts on that.

yes, i would assume they fit the right type and set the correct velocity to get enough throw and mixing.

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#3000049 22-Nov-2022 22:02

You should probably consider two multi split systems as well, one for bedrooms, the other for living areas. Simplicity, no returns, possibly cheaper.

Jase2985

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#3000074 23-Nov-2022 05:26

tweake:

your better to go undersized than oversized.

don't you mean the other way round?

agree with having a return in the entrance

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timmmay

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#3000122 23-Nov-2022 06:56

Ducted systems with temperature control need an area to put any conditioned air when the other temperature controlled rooms are up to or nearly up to heat. Airtouch calls this a "spill zone". The large the heat pump, the higher the minimum output, the more spill there is. We set this as the lounge. The practical effect of this is the spill zone sometimes / often ends up warmer than preferred. The smaller the heat pump, the lower the spill.

To balance that, you want your house to be warm even on the coldest days. We have a 10kw heat pump for four rooms, only three turned on most of the time. Even on the coldest days it had no trouble keeping the house warm. I suspect many installers oversize heat pumps because they don't really know how to size them properly.

rogercruse

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#3000123 23-Nov-2022 07:09

We had heat-pumps from Diakin installed in each bedroom and living space in our previous home... a total of seven heat-pumps. Each room was independently controlled. The advantage being that some rooms can be left unmanaged saving power. we also had solar panels on the roof to heat hot water in the 300 litre cylinder. We also had battery backup too for the lighting.

For our current new-build house we opted for a ducted system with a central heat-pump from Fujistsu with six zones. In theory, each zone is separate, but not quite true. the advantage being that the all house is warm. We had a centrally managed system for all our lighting, heating, cooling and security needs.

We decided against installing solar panels / batteries (the central heat-pump has reduced the electricity demands and we opted for Electric Kiwi and their hour-of-power each day to further reduce our power bills with needing to spend money on solar

The ducted solution is best for a busy home.... all rooms get used.

tweake

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#3000377 23-Nov-2022 16:40

Jase2985:

tweake:

your better to go undersized than oversized.

don't you mean the other way round?

no.

if you size it to the coldest weather you will have a system that will only run 100% for a few days of the year, which makes it uneconomic. for those few days put some clothes on. it also means that during the milder temps it be short cycling which is not good for efficiency and durability. if you oversize it, all that simply gets worse.

with cooling, oversizing means you don't get much moisture removal ie doesn't lower that sticky auckland humidity.

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#3000378 23-Nov-2022 16:44

timmmay:

To balance that, you want your house to be warm even on the coldest days.

actually you don't.

you want it to be maintain temp on the normal cold weather, which is not the coldest days.

eg for auckland i think design temp is 4c even tho auckland does get colder than that.

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