Central heating with positive air system

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#1571794 14-Jun-2016 16:27

Outside air doesn't need to be filtered, it's the same as opening a window.

So:

1. Air is pumped from outside into the air cavity

2. There's ducting that connects the rooms to each other, but there's no powered fans connected to the ducting?

If so call your installer, or if you don't know who that was, the manufacturer.

chimera

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#1571796 14-Jun-2016 16:30

t0ny:

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?

Wow, after 2 pics and a drawing, I'm still well confused!!

The air is pulled in and likely filtered on the outlet, or somewhere within the unit.

Are the 3 x ducted pipes (in first photo) that point downwards (almost look like straight onto the batts) - are they the outlets to 3 different rooms?

In my HRV system, it doesn't draw any air from outside the house directly, it draws the air from the ceiling (eg: the same as your first picture where you can just make out the inlet to the duct fan) The air just gets pulled in from the various gaps around your soffits etc into your ceiling. The HRV unit then filters the air, and pushes it down a number of ducted foil pipes and out to various rooms around the house.

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#1571799 14-Jun-2016 16:39

Who knew it was going to be so hard to explain :) . You are correct, basically air is being pulled from outside (with no filtering) and just airs the roof. The ducts just sit there not connected to anything. The three holes marked RD are room ducts (3 rooms) all connected to a single pipe. I fail to understand the logic of this configuration.

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#1571806 14-Jun-2016 16:46

So the "single pipe" - where does that go?

It should go to the outlet of the fan unit.

They generally just tape those onto the fan - so it could have possibly just fallen off.

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#1571809 14-Jun-2016 16:50

hrmm..that is possible that they could have fallen off. If i plug those back in, then its pretty much like opening the windows to the room so would get pretty cold at night. I need to find out what sensors it has in place to turn the ventilation on or off. I would at least expect a filter in there though to prevent unwanted smells coming into the room.

ubergeeknz

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#1571812 14-Jun-2016 16:52

So with a lot of these systems there are two fans - one brings air from outside into the roof, the other pushes air from the roof into the house. Depending on temperature differentials (outside / roof / house) they activate the various fans... maybe that's what's happening here? I can't see any other reason for there to be two fans...

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#1571832 14-Jun-2016 17:06

ubergeeknz:

So with a lot of these systems there are two fans - one brings air from outside into the roof, the other pushes air from the roof into the house. Depending on temperature differentials (outside / roof / house) they activate the various fans... maybe that's what's happening here? I can't see any other reason for there to be two fans...

I have 2 x HRV fans in my roof, however they are a good 10 metres apart, each does a different portion of the house (which has now got me thinking - how do they talk to each other, as there is only 1 x control panel...) When we first got it (9 or 10 years ago now?!) they said the size of the house will require 2 x fan units. Probably just got sucked in by the sales and marketing lady at the time... in hindsight, I would have done it differently (although we didn't quite have the selection of products that we do these days)

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#1571834 14-Jun-2016 17:07

Yeah ducts falling off would make most sense. Do you have access to the installer? Yes pushing cold air into a warm house isn't always sensible, but some systems turn the fan waaaay down at night. Even then I still have a timer, a cheap $10 one from bunnings.

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#1571839 14-Jun-2016 17:13

timmmay:

Yeah ducts falling off would make most sense. Do you have access to the installer? Yes pushing cold air into a warm house isn't always sensible, but some systems turn the fan waaaay down at night. Even then I still have a timer, a cheap $10 one from bunnings.

Yeah in the HRV's case, the fan speed varies quite a bit depending on temperature. I can see it on my iPhone whenever needed. It dials the fan speed down really low when the differential between roof and house temperatures is great (eg: the roof is really cold) In the image off my iPhone below as an example, if the roof is say 17 degrees, the fan speed may sit at 40% or more. When the roof temp is higher than the house, and roof is also above the control panel set temperature the fan will go to 100%

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#1571840 14-Jun-2016 17:14

chimera:

ubergeeknz:

So with a lot of these systems there are two fans - one brings air from outside into the roof, the other pushes air from the roof into the house. Depending on temperature differentials (outside / roof / house) they activate the various fans... maybe that's what's happening here? I can't see any other reason for there to be two fans...

I have 2 x HRV fans in my roof, however they are a good 10 metres apart, each does a different portion of the house (which has now got me thinking - how do they talk to each other, as there is only 1 x control panel...) When we first got it (9 or 10 years ago now?!) they said the size of the house will require 2 x fan units. Probably just got sucked in by the sales and marketing lady at the time... in hindsight, I would have done it differently (although we didn't quite have the selection of products that we do these days)

OK that makes sense. Sounds like the ducts have just come loose, need to be put back in place and taped on with vinyl duct tape. Then you'll be sweet again.

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#1571904 14-Jun-2016 19:42

I'm still confused about the set up. Two fans pumping outside air in right next to each other seems bizarre to me. Are there any other fan units in the set up? What is the brand/model? Are you sure it's a positive pressure system? There's not some funky suck/blow thing going on and there's a heat exchanger somewhere in there?

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#1571911 14-Jun-2016 19:47

I have connected all the pipes using duct tape and air is coming out from the ducts. To make this work better, it would be a good idea to have a humidity and temperature sensor inside the tube so that Iam not introducing too much humidity in the house. This would affect the central heating system otherwise.

The fan controller is pretty basic and just uses the room temperature but I need to find a controller which can take him it's and temperature as input

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#1571914 14-Jun-2016 19:54

t0ny: I have connected all the pipes using duct tape and air is coming out from the ducts. To make this work better, it would be a good idea to have a humidity and temperature sensor inside the tube so that Iam not introducing too much humidity in the house. This would affect the central heating system otherwise.

The fan controller is pretty basic and just uses the room temperature but I need to find a controller which can take him it's and temperature as input

Does it use a standard plug? A wifi plug plus some smart thermostats and some triggers might be an easy way of getting what you want.

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#1571917 14-Jun-2016 19:57

Yep, standard plug. I have a smart plug on the way which I can control via openhab. Would be nice to control the fan speed though but not sure how I can do that

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#1571924 14-Jun-2016 20:02

t0ny: Yep, standard plug. I have a smart plug on the way which I can control via openhab. Would be nice to control the fan speed though but not sure how I can do that

Hmm, good point. That one is a bit beyond me. If you know the brand you can probably see if anyone has figured it out before you.

The other way might be to use a humidity sensor in combination with temperature and time. I'm sort of thinking if humidity is over X% and it's the middle of the day/no-one is home, then turn on the fans at full blast until the humidity lowers to Y%? But that is just me thinking out loud.

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