Ducted Heat Pump Queries

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Handle9

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#3196046 15-Feb-2024 23:42

johno1234: If that is all true then isn't airtouch or other zone controlled ducted systems a bad idea too?

Airtouch, and other zone control systems, are a kludge. They are trying to create variable air volume systems out of constant air volume systems. When you do variable volume properly you match supply volume with the zone volume. It's a very standard, and well used control system on all sorts of commercial buildings, from airports to commercial buildings. Even then you never completely close off a branch as you will have a minimum design airflow.

The way zone systems generally work is there is a spill zone/s where you dump volume but that can create problems if the ductwork isn't suitable. They will also generally have a minimum damper position on each damper to ensure minimum airflow, if they are setup somewhat properly.

In a domestic situation the no one wants to spend the money to do it properly which is why zone controls came about. When I started working on the industry 17 years ago they were just on/off, they have gradually gotten a bit more sophisticated but they are still a kludge.

timmmay

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#3196076 16-Feb-2024 08:31

In summary, having had ducted systems with and without temperature controlled zones, they are much more useful with the control - AirTouch or similar.

I don't think Airtouch are trying to simulate a variable volume system, they just shift most of the airflow to where it's required. They have built in logic to ensure sufficient dampers are open for the airflow, but there's always going to be at least a little bit of leakage around dampers which relieves pressure. As well as a spill zone, you can and should have a bypass damper, which is another hack but a useful one, it avoids the need for a spill zone. I've never heard of a duct bursting, I've had mine for a few years and the annual inspections say the ducts are fine.

I looked at a Daikin VRV system before I got a standard system with an Airtouch. From memory it was about 50% more expensive with few practical benefits.

johno1234

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#3196096 16-Feb-2024 09:10

tweake:

johno1234:

I would want to avoid heating or cooling the entire house that way if we didn't have zone control?

i would heat/cool the entire house. its so much better for comfort, much much better for the house as heat moves moisture and even if you heat just one room your actually heating the house via one room. we have been well taught to only heat the space you use and we need to learn to use whole home heating.

I guess this is only economic due to the efficiency of heat pumps?

Handle9

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#3196325 16-Feb-2024 14:33

timmmay:
In summary, having had ducted systems with and without temperature controlled zones, they are much more useful with the control - AirTouch or similar.

I don't think Airtouch are trying to simulate a variable volume system, they just shift most of the airflow to where it's required. They have built in logic to ensure sufficient dampers are open for the airflow, but there's always going to be at least a little bit of leakage around dampers which relieves pressure. As well as a spill zone, you can and should have a bypass damper, which is another hack but a useful one, it avoids the need for a spill zone. I've never heard of a duct bursting, I've had mine for a few years and the annual inspections say the ducts are fine.

I looked at a Daikin VRV system before I got a standard system with an Airtouch. From memory it was about 50% more expensive with few practical benefits.

If you modulate a damper to a space based on load you have, by definition, a variable volume system.

timmmay

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#3196327 16-Feb-2024 14:36

Ah, I assumed variable volume related to the airflow, rather than the space.

Handle9

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#3196329 16-Feb-2024 14:40

timmmay:
Ah, I assumed variable volume related to the airflow, rather than the space.

You are varying the volume of air being supplied to the space.

The overall system will end up with variable volume as the air balance changes even though the fan runs at the same speed.

tweake

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#3196536 16-Feb-2024 20:27

johno1234:

tweake:

i would heat/cool the entire house. its so much better for comfort, much much better for the house as heat moves moisture and even if you heat just one room your actually heating the house via one room. we have been well taught to only heat the space you use and we need to learn to use whole home heating.

I guess this is only economic due to the efficiency of heat pumps?

tricky question to answer.

currently, yes the big change in the last 20 odd years is heatpumps which is why whole home heating is becoming more common.

but its more to do with people willing to spend money on heating in the first place. its always uneconomic compared to not heating at all. ie its never economic. so it has become a culture thing rather than a practical matter (which we are slowly getting away from). cheap gas/fuel didn't really exist. however there has always been lots of wood, its just most don't use it to heat the whole house. then add in that kiwis have been taught to be allergic to using power. but really its been the poor quality of homes thats made it too expensive and the lack of decent homes has been driven by other factors.

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kzw4nc

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#3202600 3-Mar-2024 10:27

Pricing sounds about right. I've just had ducted heat pump installed for a 105sqm 1910 house in Wellington. Outlet vents are in the ceiling and a return is in the hallway wall by floor level. House is only really insulated in the ceiling, and has some door/window gaps typical of a house of that age.

It's a Rinnai. Don't get a Rinnai. Specifically Rinnai DSNR13B1 kW Rating: 12.5kW Cooling, 13.0kW Heating Airflow: 1120 l/s

It's been a bad experience to date. It's noisy - so rubber dampers have had to be installed on the feet of the device. The controller is highly confusing; and the instruction manual makes no sense - after 3 months I still don't understand how to use it and neither do the installers (and Rinnai ignores them when they ask for help). It's been effective in 'dry' mode in de-humidfying the house; and the 'cooling' mode works, but you don't need that much in Wellington. The 'heat' mode is problematic however - I've only been able to use it in the last week in the mornings (as it has been too warm to require any heating until now). My issue with the heating is that fogs up all the windows and mirrors in the house for an hour or so until they clear! The temperature is around 11C outside, and the inside temperature about 19C (ie it barely needs heating by I want to test it!).

In hindsight I should have done heaps more reading up on heat pump options, and watched a lot more youtube videos, and looked at Geekzone. I assumed buying a new heating system was like buying a new fridge, as it turns out it's a really hazardous activity for a consumer!! At the moment I just have a $20K lump of junk in the roof space...

johno1234

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#3202609 3-Mar-2024 10:37

Wow that is terrible. I would be demanding action from Rinnia, and if they don't sort this out, take a claim to the disputes tribunal to get your money back.

Who installed it?

RunningMan

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#3202615 3-Mar-2024 10:59

kzw4nc:My issue with the heating is that fogs up all the windows and mirrors in the house for an hour or so until they clear!

That's pretty normal for ANY heat pump when it is moved from cool to heat cycle. Any residual moisture in the unit (it will collect and drain a litre or so per hour in cooling) will evaporate as the temp comes up, then condense on cold surfaces in the room. If a ducted system is set up to draw some fresh air at the same time it will reduce the problem, but the main thing is stop swapping from cool to heat (which you have probably doing as you are testing), it's just making the problem worse. In general terms, keep it on cool in summer, heat in winter. You'll see the same thing if you turn the AC off in a car - everything fogs up for a couple of minutes.

tweake

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#3202619 3-Mar-2024 11:20

kzw4nc:

It's a Rinnai. Don't get a Rinnai. Specifically Rinnai DSNR13B1 kW Rating: 12.5kW Cooling, 13.0kW Heating Airflow: 1120 l/s

It's been a bad experience to date. It's noisy - so rubber dampers have had to be installed on the feet of the device.

My issue with the heating is that fogs up all the windows and mirrors in the house for an hour or so until they clear! The temperature is around 11C outside, and the inside temperature about 19C (ie it barely needs heating by I want to test it!).

the rubber dampeners is an installation issue. the unit is meant to be installed on rubber dampers in the first place as per installation manual. that makes me wonder what other short cuts was taken.

the fogging is more of a house issue, warm moist air hitting cold windows. a couple of things could be happening. the coils could be damp because its getting damp air on cold coil, because you have the unit setup outside (in ceiling is effectively outside). could also be the drain isn't draining the pan out. ie the unit is not level or has other drainage issue. it can also be that the ceiling is full of very moist air, especially if its connected down to under the floor. i have seen walls with no top and bottom plate before. if its brick outside it may have a vent space behind it which allows wet air from the ground up into the ceiling.

i would check ceiling moisture levels, also check the ducts for leaks especially on the return (sucking in ceiling air). btw having returns at ground level is weird. the problem there is those old houses leak a ton of air through the floor. so you could be suck in moisture up through the floor. (also i'm assuming the unit is installed in the ceiling and not something dumb like under the house above the dirt.

also check duct leakage on the pressure side, leaks will cause the house to depressurize and suck in cold outside air (which could be wet if its up through the floor).

also pay to have humidity gauge and check the house is getting enough ventilation.

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