Alterations to existing PPV system

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NeilnCharles

10 posts

Wannabe Geek

#285733 13-May-2021 21:46

Evening everyone, I have an existing system, PPV I believe. I want to make some changes and keen to get some thoughts and opinions, maybe some experiences but definitely needing advice! I have seen and heard enough to know I am not going to buy a new system.

Sorry this got long...

Basically, the system now (installed by previous owners) takes air from the ceiling space and pumps it into the hall. As I have a tile roof which is not air tight (literally can see the light coming through around the tiles) the temperature is the same as the outside air, there is no heat held in the ceiling. The duct now goes into a plenum box which has a heater it in, but on a cold night even on the highest heat setting (2kW) and lowest air speed it barely takes the chill off it.

I am wanting to achieve two things, one is to bring in enough outside air to prevent condensation, two is warming the space.

As I keep the lounge/dining quite warm by fireplace (26-30°, yes I like the heat) I would like to take some air from that space and bring it into the plenum box with the ceiling space air. I'm thinking changing the ceiling space duct to 50mm and using 100mm duct (insulated, about 8m run) from the dining room.

Hoping the 1/3rd fresh air is enough to lessen or stop condensation, and the 2/3rd's warm air is enough to heat, or at least not cool.

So questions are,

Anyone done this?

Does it make sense from other peoples experiences?

Any general advise?

Some additional thoughts,

There is an existing controller for the fan and heater which I would like to keep.

But I would also like to use a thermostat device to control the fan on/off, which I guess would need to cut power to the fan and heater (so i'll need a two-pole switch (solenoid?) after the controller.

Also I would like it to turn on/off based on the temperature in the lounge/dining, or ideally lounge/dining and hall. This may be getting very complicated? Reason been once I go to bed it is pointless running all night, the lounge/dining will cool down and it'll start bringing in colder air. But I would like to to run another hour or two at least, but maybe best to just use a timer.

Keen for thoughts...

timmmay

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#2707331 14-May-2021 07:36

I also found ceiling mounted heating fairly ineffective. Heating within the houses insulated envelope is more effective, though ducted heat pumps use insulated pipes (R0.6) that help a bit. Ducted heat pumps use ducts that range from 200mm (distribution) to 400mm (return air) - almost half a meter for the big ones.

In your place I would probably put in a heat transfer system independent of the ventilation system, so you have flexibility and don't mess with the controller. To move enough air to be useful I'd have thought you'd want 200mm ducting and diffusers. Input diffuser probably a grill directly over the fire (air will be 50 degrees plus), output diffusers you'll want to make sure they're downjet style otherwise the warm air will just collect at the ceiling. Looks like these cost $300 to $800 depending on brand / size.

If you really want to use your current system I guess you could do it. You'd lose the benefit of good quantities of drier / fresher outside air. I'd go to 150 to 200mm ducting to get enough airflow to make it worthwhile - my ventilation system uses 150mm ducting, my heat pump 200 - 400. You'd have to check the existing motor is worthwhile. Simx downjet or the MDO on this page.

You could use a Wifi timer like the TP-Link Kasa instead of a thermostat. Not as effective but much easier to install.

NeilnCharles

10 posts

Wannabe Geek

#2707642 14-May-2021 16:48

Thanks Timmmay, Ideally i'm looking to do this on the cheap, not buy a new system. I have a 200mm diffuser which i'm happy to run with for now and can change it later if there is a need. Noted regarding larger duct size, I don't think 200+ is required from the lounge/dining but maybe bigger than 100.

Wi-Fi timer could work, would just have to check the fan + heater comes in under 10A.

timmmay

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#2707650 14-May-2021 17:20

I guess you can do your plan. What's the throughput of your fan? You should check that it can move enough air to be worthwhile, I'd check against the specs of a heat transfer system. I'd say 150mm duct is the minimum you'd want, but it depends on the fan and diffuser size.

NeilnCharles

10 posts

Wannabe Geek

#2707839 15-May-2021 10:59

Haven't checked that yet but can replace the fan if needed.