Need Advice on Ducted Heat Pump and Ventilation System

Forums › Home Workshop DIY › Need Advice on Ducted Heat Pump and Ventilation System - Which of the Two Options?

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Dingbatt

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#2777178 13-Sep-2021 06:56

timmmay:The zoned ones with automatic adjustments would seem to be more adaptable and probably need less design.

Yeah, nah.

In a high volume, low pressure system like ducted aircon, a change in flow rate in any duct will affect the flow rate in all the others. Unless the system is correctly designed it will produce surging and hunting between zones. Even in an un-zoned system opening or closing a door will affect the flow rate to other rooms.

While ours is un-zoned, I looked at the calculations the engineer did before our install. It involved loads and flow rates for each room and the ducting was sized accordingly. The downside of the way it is installed is that to effectively zone now will require individual room control rather than just the bedroom end of the house from the living end.

“We’ve arranged a society based on science and technology, in which nobody understands anything about science technology. Carl Sagan 1996

rogercruse

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#2777182 13-Sep-2021 07:38

We installed six high wall heat pump units (four bedrooms, media & family rooms) in our previous home and controlled each room separately. The advantage being ultimate room control and the disadvantage being that each room would take forever to warm up. We then settled on leaving the family room unit on all the time so that warmth would spread around the house.

For our current house we installed a ducted system with six zones. No more ice-cold rooms and the whole house is warm. We also installation of a heat exchange system from Cleanaire to add fresh clean air into the ducts, this reduces the overall co2 levels and we wake up refreshed. A final advantage being we don't need to adjust the settings regardless of what the weather we're having. As the cost of running the two systems would be similar, we're happier with our ducted solution.

timmmay

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#2777191 13-Sep-2021 08:20

Dingbatt:

Yeah, nah.

In a high volume, low pressure system like ducted aircon, a change in flow rate in any duct will affect the flow rate in all the others. Unless the system is correctly designed it will produce surging and hunting between zones. Even in an un-zoned system opening or closing a door will affect the flow rate to other rooms.

While ours is un-zoned, I looked at the calculations the engineer did before our install. It involved loads and flow rates for each room and the ducting was sized accordingly. The downside of the way it is installed is that to effectively zone now will require individual room control rather than just the bedroom end of the house from the living end.

I don't fully understand. Our unit has electric dampers in the ceiling space opening and closing depending on the temperature in each room. Each room has a grill for return air, though it works fine if doors are open or closed. I'm not really sure what you mean by surging or hunting. The only problem we really have is the spill zone overheating sometimes, which I explained above.

Pretty sure no calculations were done at all for our system and it's worked well so far. Two large ducts come off the ceiling unit, splitting into smaller ducts for each room. The large lounge has two diffusers, all other rooms have one.

timmmay

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#2777276 13-Sep-2021 11:47

Also, upgrade to the thicker R1.0 insulation. I did some estimates based on my limited knowledge, from memory it cut heat loss in our case down from about 30% to about 15%, ie about 1.2kw less lost in the ceiling cavity.

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