Central heating with positive air system

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t0ny

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#196790 12-Jun-2016 20:46

I have a daikin central heating system and a positive air system in my new house. Is there any benefit in having both running? Iam thinking of setting up open hab and have couple of sensors around the house as the central heating is only appears to be using the temperature it can sense where the controller is located. If the positive air system has some benefit i can perhaps look at switching it on or off using openhab depending on the situation.

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#1570714 12-Jun-2016 21:00

They're for different things. Central heating heats and the positive pressure system essentially dries/dehumidifies the air. The central heating will be much more effective with dry air, as wet air hold more heat.

In terms of automation, our old DVS positive pressure system had some (basic) smarts about not circulating dry/roof air when the temperature in the roof was lower than that in the house (winter mode). Similarly, you could choose summer mode and it wouldn't circulate hotter air when the roof was hotter than the house. The winter/summer selection was manual though. If you wanted to get cleverer, you could have some kind of calendar/seasonal setting?

timmmay

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#1570812 13-Jun-2016 07:48

You'd probably be better off with an integrated system, but changing would be expensive. Personally I run my cheap old PPV system on a timer, in summer I run it morning and evening, in winter I run it during the day. All year round I run it occasionally in the evening to reduce cooking smells, and in summer I might run it late at night. I can hear it and it bugs me slightly.

I would run the PPV system at different times from the heating system, otherwise you're just pushing your warmed air out of the house.

t0ny

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#1570813 13-Jun-2016 08:01

Thanks, i dont have a temperature sensor in the roof at the moment so need to find something that will work with openhab. It would make sense to not run the PPV if the roof air temperature is less than the house unless i want to cool the house down. With turning the PPV off at night during winter, arent you not making use of any hot air sitting in your roof space?

timmmay

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#1570814 13-Jun-2016 08:08

I don't use the air from the roof cavity any more. I have a very old house, the ceiling cavity is filled with dust, rat droppings (from before I owned the house), cobwebs, etc. The white sock filter went black within a few weeks of putting a new filter in. I extended the intake so it now draws fresh clean air from outside the house. In winter you have to turn it off around 4pm before people light fires otherwise your house smells like smoke. It did give the house a small boost in temperature, but not enough to be worth it. But once the sun goes down the roof temperature drops to be the same as outside quickly - I put temperature sensors up there to check.

PPV vendors tell bald faced lies in their sales pitches.

t0ny

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#1570865 13-Jun-2016 10:26

Been doing some additional research. Some interesting facts:

The New Zealand Building Code requires homes to ventilate using outdoor air to maintain air purity. Ventilation systems that draw air from the roof space and not directly from outside do not comply with ventilation standard NZS4303:1990 "Ventilation for acceptable indoor air quality". They cannot be used to comply with the Building Code Acceptable Solution for ventilation.

and, a research report on ventilation systems states:

An ideal control system for forced air delivery from the roofspace clearly needs to take account of the temperature and humidity in both spaces. With this data, the system will be able to determine when operation will reduce the relative humidity in the building.

My PPV system doesnt appear to be getting the outdoor air at all :)

timmmay

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#1570867 13-Jun-2016 10:29

It cost $50-$100 to get extra ducting and an external vent thingy to change my ventilation system. The vendor told me it wouldn't work, the motor wasn't powerful enough, but it works fine.

t0ny

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#1571688 14-Jun-2016 14:28

It gets bit interesting. I had another look and i can see two circular duct fans pulling in air into the roof from outside. The ducts in each room has those foil pipes leading to where the cirular duct fans are but they are just sitting there, not connected to anything. Is there any reason for that (besides letting heat escape into the roof space) or has the installer not finished the job.

timmmay

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#1571692 14-Jun-2016 14:31

t0ny:

It gets bit interesting. I had another look and i can see two circular duct fans pulling in air into the roof from outside. The ducts in each room has those foil pipes leading to where the cirular duct fans are but they are just sitting there, not connected to anything. Is there any reason for that (besides letting heat escape into the roof space) or has the installer not finished the job.

Can you show a photo? Sounds to me like the installer hasn't done their job. You're not getting any forced air ventilation and you've got big holes in the ceiling.

mdf

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#1571694 14-Jun-2016 14:32

t0ny:
It gets bit interesting. I had another look and i can see two circular duct fans pulling in air into the roof from outside. The ducts in each room has those foil pipes leading to where the cirular duct fans are but they are just sitting there, not connected to anything. Is there any reason for that (besides letting heat escape into the roof space) or has the installer not finished the job.

If I read that right, that sounds completely dumb. Ducts to nothing? Photo?

mdf

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#1571696 14-Jun-2016 14:33

mdf:
t0ny:
It gets bit interesting. I had another look and i can see two circular duct fans pulling in air into the roof from outside. The ducts in each room has those foil pipes leading to where the cirular duct fans are but they are just sitting there, not connected to anything. Is there any reason for that (besides letting heat escape into the roof space) or has the installer not finished the job.

If I read that right, that sounds completely dumb. Ducts to nothing? Photo?

And sorry I didn't mean that as it sounded. Installation = dumb, not the question.

t0ny

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#1571697 14-Jun-2016 14:36

Here goes:

You can see the three pipes sitting on the ceiling with the two duct fans above it

timmmay

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#1571714 14-Jun-2016 14:53

I think we need a wider picture. I can't make much sense of that.

t0ny

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#1571717 14-Jun-2016 14:58

Pretty dark up there and the camera flash doesnt get the whole area. Basically, the pipes from each room merge as per below:

Then one end of it is sitting on the cieling as per the other pic above. Two of the silver pipes connect from outside to the duct fan

timmmay

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#1571723 14-Jun-2016 15:07

Sound be a fan sucks in air from somewhere, pushes it into ducting that goes into each room. Sounds like the didn't connect the ducts to the fans. Maybe you could draw a diagram, because it sounds like what you're saying is the fans spin away but do nothing...

t0ny

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#1571742 14-Jun-2016 15:20

Hope this makes more sense:

Shouldn't the outside air be filtered? Is it hard to put in a sock filter in there?
Should the outlet from the duct fan be connected to the pipe that is lying below the duct fan?

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