Brivis gas central heating - adding fresh air ventilation

Forums › Home Workshop DIY › Brivis gas central heating - adding fresh air ventilation

1 | 2

snowfly

543 posts

Ultimate Geek

#3250542 18-Jun-2024 18:57

tweake:

you need a fan for the ventilation. just putting a duct to the return won't do anything. a simple cheap ventilation system kit would work ok. hook that up to the return or vent next to the return (which is easier to get to work when heating is off).

you can't just put a damper in that will block off the return and feed in outside air. that can cause damage to your house as it will pressurize the living hell out of the house.

@tweake - perhaps I wasn't clear enough, I wasn't meaning 'just put a duct'.

The damper was going to go in between the return intake and the brivis unit (which has the fan inside), so the brivis unit will suck air from which ever intake duct is open (either return vent in house, or external intake)

So:
Damper in position 1 (normal): duct between inside return vent and brivis unit is OPEN, and duct to outside is CLOSED, meaning brivis unit sucks in air from inside the house, and recirculate back around house
Damper in position 2: duct between return vent and brivis unit is CLOSED, duct to outside is OPEN, brivis unit when running in fan mode will suck air from outside and then push around the house

Isn't that essentially what a summer air system does on any other heat trans / ventilation type system?

tweake

2391 posts

Uber Geek

#3250544 18-Jun-2024 19:03

snowfly:

Damper in position 2: duct between return vent and brivis unit is CLOSED, duct to outside is OPEN, brivis unit when running in fan mode will suck air from outside and then push around the house

that will damage your house. do not do that whatsoever.

the difference between that and a ventilation system is flow rate and pressure. ducted system runs a big fan which will pressurize the hell out of the house. a ventilation system puts in tiny amounts of airflow and creates tiny tiny little amount of pressure.

snowfly

543 posts

Ultimate Geek

#3250555 18-Jun-2024 19:41

tweake:

that will damage your house. do not do that whatsoever.

the difference between that and a ventilation system is flow rate and pressure. ducted system runs a big fan which will pressurize the hell out of the house. a ventilation system puts in tiny amounts of airflow and creates tiny tiny little amount of pressure.

@tweake So if I understand your statement right, you are saying the fan in a Brivis ducted unit is substantially more powerful (and can push more air) when compared to a standard ventilation fan, and this will cause damage to the house?
Please explain said damage?

Our current Brivis unit is an older model, MPS ME 20i, which I can't find specs online for, but brivis have a changeover/upgrade doc which suggests the MPS ME 20i is a close equivilent to the newer SP421U model.
And according to newer docs, the SP421U model has an airflow rate of 621 L/s

If I lookup the fan specs of the SmartVent SV04L system (4 room home ventilation system), the fan has a flow rate of 296 l/s, 1066m3 /hr (at 0 Pa)

So you're saying a 621 L/s flow brivis fan (running at max speed) will damage a house, but a 296 L/s flow ventilation fan is OK?

What about running the brivis fan mode at only half speed (it has multiple speed options), e.g. at 300 L/s flow, similar to a SmartVent system, any issues?

Curious to know you're thoughts and background on this, so I can learn, thanks.

timmmay

20574 posts

Uber Geek

Trusted

Lifetime subscriber

#3250560 18-Jun-2024 20:09

tweake:

timmmay: When I do my daily ventilation, I crack open the window in one bedroom so that I can control where the air leaves the house. It's usually on the side it's not raining.

thats defeats a lot of the ventilation.

the whole idea of ppv is that it leaks out of each room. if you make it leak out of one room, then only one room is getting ventilation as all the air will go to that room. with standard houses there is no need for to open a window. it has enough normal leakage, plus the bath fans and rangehoods to leak through.

Nah. I can feel where the air goes by standing under the ducts. Plus I haven't fully explained my setup or my goals.

tweake

2391 posts

Uber Geek

#3250636 18-Jun-2024 21:22

snowfly:

tweake:

that will damage your house. do not do that whatsoever.

the difference between that and a ventilation system is flow rate and pressure. ducted system runs a big fan which will pressurize the hell out of the house. a ventilation system puts in tiny amounts of airflow and creates tiny tiny little amount of pressure.

@tweake So if I understand your statement right, you are saying the fan in a Brivis ducted unit is substantially more powerful (and can push more air) when compared to a standard ventilation fan, and this will cause damage to the house?
Please explain said damage?

Our current Brivis unit is an older model, MPS ME 20i, which I can't find specs online for, but brivis have a changeover/upgrade doc which suggests the MPS ME 20i is a close equivilent to the newer SP421U model.
And according to newer docs, the SP421U model has an airflow rate of 621 L/s

If I lookup the fan specs of the SmartVent SV04L system (4 room home ventilation system), the fan has a flow rate of 296 l/s, 1066m3 /hr (at 0 Pa)

So you're saying a 621 L/s flow brivis fan (running at max speed) will damage a house, but a 296 L/s flow ventilation fan is OK?

What about running the brivis fan mode at only half speed (it has multiple speed options), e.g. at 300 L/s flow, similar to a SmartVent system, any issues?

Curious to know you're thoughts and background on this, so I can learn, thanks.

all heating units have more airflow than ventilation systems. how much depends on the system. a gas system will generally have less airflow than a heat pump system. but it also comes down to what pressures they can handle. heating systems handle much higher pressures than ventilation systems. ventilations systems run big fans at slow speeds, so they make less pressure which is why most use fairly large ducts for the amount of air. run a ventilation fan at full speed and you will be surprised. thats a long way of saying hvac system run higher flows at higher pressures. far to much air flow for ventilation (it may not be able to go slow enough for ventilation rates). one of the sites mentioned 5ach for the heater, ventilation is 0.35 ach. big difference in flow. also rated flows and what you get are way different especially with variable speed ventilation.

its all going to depend on whats fitted, what size house and what air leakage the house has. what damage depends on the house. eg older homes can have ceiling panels or plaster work which moves in the wind which can be lifted up by a big enough fan, but they also can leak so much it does nothing. a renovated house who knows. newer homes can have building wrap issues. damage might be tiny, but it adds up when its being used every day.

i would not recommend even running it on lower speed, simply because someday someone is going to forget why it was set like that and return it to default. also what happens when things fail. not good for heating if the damper fails or speed control fails. its best practice to let the machines do their jobs separately if at all possible (but not always practical). for something like this its far better to leave the heating in default config and add ventilation to it, and let the ventilation system worry about its own flow rates. that way your not screwing with the heating system and fail of either is not going to effect the other.

to give some idea, there has been quite a few issues with heat transfer systems due to lack of return air. they sucked so much air out of the living room they back drafted the fireplace and filled the house with smoke. when you screw with pressures weird stuff can happen.

also don't over ventilate. ventilation pulls in humidity (especially auckland/northland) so going less ventilation can result in a drier home.

tweake

2391 posts

Uber Geek

#3250771 19-Jun-2024 11:34

snowfly:

tweake:

that will damage your house. do not do that whatsoever.

the difference between that and a ventilation system is flow rate and pressure. ducted system runs a big fan which will pressurize the hell out of the house. a ventilation system puts in tiny amounts of airflow and creates tiny tiny little amount of pressure.

@tweake So if I understand your statement right, you are saying the fan in a Brivis ducted unit is substantially more powerful (and can push more air) when compared to a standard ventilation fan, and this will cause damage to the house?
Please explain said damage?

Our current Brivis unit is an older model, MPS ME 20i, which I can't find specs online for, but brivis have a changeover/upgrade doc which suggests the MPS ME 20i is a close equivilent to the newer SP421U model.
And according to newer docs, the SP421U model has an airflow rate of 621 L/s

If I lookup the fan specs of the SmartVent SV04L system (4 room home ventilation system), the fan has a flow rate of 296 l/s, 1066m3 /hr (at 0 Pa)

So you're saying a 621 L/s flow brivis fan (running at max speed) will damage a house, but a 296 L/s flow ventilation fan is OK?

What about running the brivis fan mode at only half speed (it has multiple speed options), e.g. at 300 L/s flow, similar to a SmartVent system, any issues?

Curious to know you're thoughts and background on this, so I can learn, thanks.

i found the specs for that unit, however there is 3 different versions and the difference is airflow, 500 to 700l/s

for a 200sqm house it does around 5ach and it can do upwards of 175pa total pressure. in contrast ventilation flow rate (0.35 ach) is around 50 l/s, ie a 10th of the gas heater (if its the low airflow version). i highly doubt it will go slow enough to achieve that.

now the interesting thing is that a reasonably good house air leakage with a blower door test is about 5ach at 50pa. that flow and pressure is enough to lift carpet off the floor and that heater system could easily achieve those flow rates and pressure. the more air tight the house the worse that gets (passive house under 1ach, original 60's house 5-10 ach). for proper calcs need to work out the volume of your house.

so yeah really bad idea trying to use an hvac system fan as the ventilation fan.

snowfly

543 posts

Ultimate Geek

#3250774 19-Jun-2024 11:43

Thanks for the detailed explanations, appreciated.

I was hoping to re-use the existing ducts under the house that are already instead, rather than spending thousands installing a separate ducted system in the roof, but sounds like that might be the way to go, to have 2 separate systems.

Although I do wonder then if the 2 systems (heating coming up under floor), and ventilation (coming down from roof/outside) will then compete with each other, or make the heater run more?

I guess now to look into whether a 2/3/4 bedroom outlet ventilation system, or whether a single outlet ventilation system could suffice (it's not like our house is dripping wet inside, as renovation/insulation has improved it).

On another note, our brivis heater system when run in Auto heating mode (with schedule program), when the heater isn't running (e.g. programmed temp is 18, current temp is 19), the FAN runs at low speed (10%) to keep circulating air around the house. And when the heater fires back up, the fan runs at full 100% speed.

Should this 'auto fan' behaviour inbetween heating cycles be turned off if we install a ventilation system, as to not compete with each other? Or would it complement it?

Equinox IT

Cloud spending continues to surge globally, but most organisations haven’t made the changes necessary to maximise the value and cost-efficiency benefits of their cloud investments. Download the whitepaper From Overspend to Advantage now.

tweake

2391 posts

Uber Geek

#3250785 19-Jun-2024 12:08

snowfly:

Should this 'auto fan' behaviour inbetween heating cycles be turned off if we install a ventilation system, as to not compete with each other? Or would it complement it?

keeping that fan on is helpful. very useful to have something circulating the air.

i would not install 3-4 outlet ventilation system. i would either add a ventilation system to the return or put a single outlet by the return. there is pro's and cons of course but thats cheap and reliable and will work perfectly fine with heater running on auto fan.

1 | 2