New DVS EC Climate Control

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timmmay

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#3373388 14-May-2025 22:49

When the absolute humidity outside is below the absolute humidity inside, turning on positive pressure ventilation reduces the inside humidity. It is a bit slow, but it does work, and obviously the bigger the difference in humidity the faster it works.

It doesn't need to be below zero degrees to work in my experience. I can see humidity change as soon as ppv comes on, but significant changes take hours.

openmedia

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#3373391 15-May-2025 00:16

freitasm:

@openmedia how can heatpumps help with humid interiors? Just using Heat won't dry. We tried with the DRY option but that's basically blasting cold air.

We've tracked this via a bunch of Xiaomi temp/humidity sensors in each room plus Home assistant.

First we open windows a lot for fresh air subject to outside temperature / humidity.

If humidity is high, especially upstairs, we run dry mode which pulls damp air from the hall and pushes dry air into the bedrooms. We see a noticeable drop in overall humidity. On a hot humid summer day we tend to use Dry mode over cool to reduce overall humidity, especially when we want to sleep.

In winter we'd use dry mode to help rebalance some of the rooms when the ambient temperature isn't super low.

Overall we're happy with the results we're seeing and the house never smells of damp.

Generally known online as OpenMedia, now working for Red Hat APAC as a Technology Evangelist and Portfolio Architect. Still playing with MythTV and digital media on the side.

tweake

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#3373469 15-May-2025 10:07

SomeoneSomewhere:

The ideal is heat-recovery ventilation or energy-recovery ventilation. You bring in fresh outside air, eject stale inside air, and run each of them through a heat exchanger so that the already cooled/heated outgoing air cools/warms the untempered incoming air.

ERV also transfers moisture from one set of air to the other. Many places with serious winters need to add humidity to the air in winter.

when the erv is transferring moisture across it releases/reclaims the heat from the evaporation of the moisture. that makes it a lot more efficient than an hrv.

however a better way to look at it is that an hrv keeps indoor heat inside and outdoor heat outside. an erv also does that with moisture. eg when it rains (and then the sun comes out and it evaporates) the humidity goes way high (90-100%), an erv keeps that moisture outside. an hrv or pps will bring that moisture inside. but, as the erv is also keeping indoor moisture inside, you need a dehumidifier to keep indoor humidity at the level you want.

richms

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#3373474 15-May-2025 10:24

timmmay:

When the absolute humidity outside is below the absolute humidity inside, turning on positive pressure ventilation reduces the inside humidity. It is a bit slow, but it does work, and obviously the bigger the difference in humidity the faster it works.

It doesn't need to be below zero degrees to work in my experience. I can see humidity change as soon as ppv comes on, but significant changes take hours.

The problem is that the cost to heat that slightly lower humidity air is way more than running a dehumidifier would cost you, and you get the free heat from that as well.

If you had an actual HRV, that would lower that cost significantly and it would probably make sense to reduce humidity that way, but blowing the humid indoor air out thru the building where it can condensate on the colder structure and cause problems is not a good solution.

Richard rich.ms

timmmay

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#3373477 15-May-2025 10:35

richms:

The problem is that the cost to heat that slightly lower humidity air is way more than running a dehumidifier would cost you, and you get the free heat from that as well.

If you had an actual HRV, that would lower that cost significantly and it would probably make sense to reduce humidity that way, but blowing the humid indoor air out thru the building where it can condensate on the colder structure and cause problems is not a good solution.

That's true. We mitigate that by running the positive pressure system for limited times, at selected times of the day. For example in winter we do an hour or so in the middle of the day, and a half hour in the evening, which isn't much but keeps the air fresh. On nice days I add a bit more time, I have a single button in home assistant that turns on PPV and ducted system fan for an hour. We crack open a window so that it gives the air an egress point.

I did look at getting a heat recovery ventilation system a while back, Cleanaire I think it was, but never got around to it. I've just sent them another message to get an updated estimate.

tweake

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#3373488 15-May-2025 11:13

richms:

The problem is that the cost to heat that slightly lower humidity air is way more than running a dehumidifier would cost you, and you get the free heat from that as well.

If you had an actual HRV, that would lower that cost significantly and it would probably make sense to reduce humidity that way, but blowing the humid indoor air out thru the building where it can condensate on the colder structure and cause problems is not a good solution.

a lot of things mixed up in that.

blowing humid air around the house is not a problem, in fact it helps DRY the house. firstly humidity equalizes around the house fairly quickly, so even if you don't blow that humid air around, that moisture is going to get into that room that has the cold spot. air movement helps stop condensation forming and helps dry the area. thats why they like to blow air behind curtains to stop "crying windows". so we want air circulation. ventilations system can be pretty low, hvac system or ceiling fans are much better.

having an hrv doesn't effect humidity and the required dehumidifier is still big as your dehumidifying all that ventilation air. using an EVR keeps most of the outdoor humidity out so you only need a small dehumidifier to deal with the indoor generated moisture.

however what upsets all this, is how air leaky the house is. not much point in it when your air leakage is as much or more than your ventilation air rate, which is much the norm for kiwi houses.

esawers

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#3373493 15-May-2025 11:23

We had HRV installed in a 1950's brick and tile house in Christchurch in about 2008. When we left we rented the house out.

We had a call last week to say the fan had stopped working in the roof and the windows were covered in condensation. They sent photos of all of the windows absolutely crying. We found a secondhand fan unit off marketplace, quick swap and the house is back to being dry. The manual did say it takes a few weeks to get to its full potential.

But for a system that is barely noticed and hardly anyone understands (the tenants keep asking why it isn't heating in winter) it does what was promised.

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tweake

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#3373504 15-May-2025 11:47

esawers:

We had HRV installed in a 1950's brick and tile house in Christchurch in about 2008. When we left we rented the house out.

We had a call last week to say the fan had stopped working in the roof and the windows were covered in condensation. They sent photos of all of the windows absolutely crying. We found a secondhand fan unit off marketplace, quick swap and the house is back to being dry. The manual did say it takes a few weeks to get to its full potential.

But for a system that is barely noticed and hardly anyone understands (the tenants keep asking why it isn't heating in winter) it does what was promised.

doing what hrv promised is somewhat debatable. thats where a lot of complaints and misinformation about heating the house in winter comes from.

"crying windows" does not mean the house is damp, its normal for single glazing. the trick is they blow air down the back of the curtains across the window and you get clear windows, but it removes a lot of the insulation value of the curtains. this is why in some of the manuals they say to install the outlets within a certain distance of the windows and why they often have multiple outlets in a room.

SomeoneSomewhere

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#3373567 15-May-2025 12:37

tweake:

SomeoneSomewhere:

The ideal is heat-recovery ventilation or energy-recovery ventilation. You bring in fresh outside air, eject stale inside air, and run each of them through a heat exchanger so that the already cooled/heated outgoing air cools/warms the untempered incoming air.

ERV also transfers moisture from one set of air to the other. Many places with serious winters need to add humidity to the air in winter.

when the erv is transferring moisture across it releases/reclaims the heat from the evaporation of the moisture. that makes it a lot more efficient than an hrv.

however a better way to look at it is that an hrv keeps indoor heat inside and outdoor heat outside. an erv also does that with moisture. eg when it rains (and then the sun comes out and it evaporates) the humidity goes way high (90-100%), an erv keeps that moisture outside. an hrv or pps will bring that moisture inside. but, as the erv is also keeping indoor moisture inside, you need a dehumidifier to keep indoor humidity at the level you want.

My understanding is that many of them (at least, commercial units) can adjust dampers internally to switch between simple balanced ventilation ('free cooling'), HRV mode, and ERV mode as needed.

Getting the BMS people to actually automate them effectively is like pulling teeth.

tweake

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#3373583 15-May-2025 13:39

SomeoneSomewhere:

My understanding is that many of them (at least, commercial units) can adjust dampers internally to switch between simple balanced ventilation ('free cooling'), HRV mode, and ERV mode as needed.

Getting the BMS people to actually automate them effectively is like pulling teeth.

on ERV you never want to use the "free cooling" setup as it lets in a ton of moisture and stuffs up your humidity, which in turns means the dehumidifier starts up which in turn adds heat.

on HRV its possible, because humdity is being ignored, however you need to look at how useful it is. the ones i have seen have come programmed to open up the bypass at rather cold temps. you need a decent temp difference for it to work, especially with such low airflows. how many places are going to get hot enough during the day to require cooling then drop to 5c outside rather rapidly, almost none. certainly none in nz. now you could set it to open at say 20c, but then it has almost no temp difference and would require a massive amount of airflow to achieve anything. so nz simply doesn't have the climate to make it useful and anyone with a decent enough house to run an HRV core should be using a ERV core anyway.

in the commercial world its done with HVAC which has a lot larger airflow. so its something that could be done on a ducted heat pump (ducted hvac might be 4 ach airflow compared to 0.5 ach for ventilation), but the amount of money you would save in cooling the house, would be less than what the gear costs.

the free cooling thing on hrv/erv home ventilation is really just a sales pitch.

SomeoneSomewhere

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#3373584 15-May-2025 13:43

Yeah, the consideration there was commercial spaces with no AC or dehumidification. Free cooling for when cooling is desired; HRV mode when cooling is not needed or heating is running. That wasn't ERV but I doubt the scenario is much different.

The space had major overheating issues until the software was setup to control the HRV dampers. I think they oversized the ventilation units to provide marginal cooling instead of fitting AC for cost & energy reasons.

tweake

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#3373587 15-May-2025 14:02

SomeoneSomewhere:

Yeah, the consideration there was commercial spaces with no AC or dehumidification. Free cooling for when cooling is desired; HRV mode when cooling is not needed or heating is running. That wasn't ERV but I doubt the scenario is much different.

The space had major overheating issues until the software was setup to control the HRV dampers. I think they oversized the ventilation units to provide marginal cooling instead of fitting AC for cost & energy reasons.

oversized ventilation, especially for a crowded space. a situation that doesn't really exist with residential.

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