Panasonic vs Mitsubishi ducted heat pump and ventilation solutions

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468 posts

Ultimate Geek
+1 received by user: 93

#3433357 11-Nov-2025 14:22

AlDrag:

Kickinbac:

This seems like a lot of work and cost when you could just run the ducted unit on 'fan only' mode at lowest fan speed and the lossnay on to get the same result.

But if you've been running "cooling" mode, then you will have lots of moisture built up on your coil and thus will get all blown into your house when you run fan mode directly after? I experience this now.

This shouldn't really be a problem. Once the moisture is condensed on the coil it drains into the drain pan and out the condensate pipe. When cooling turned off, the air flow should dry the coil fairly quickly unless its super humid. Sure some must get reabsorbed into the air stream but the majority will drain away. If humidity is a problem, it best to keep the AC unit running on cooling.

I've only ever done this in commercial systems but you can put the AC system on cooling to dry the air, then reheat the room or supply air with electric heating to get back to a comfortable temperature.

AlDrag

280 posts

Ultimate Geek
+1 received by user: 27

#3433359 11-Nov-2025 14:25

Kickinbac:

This shouldn't really be a problem. Once the moisture is condensed on the coil it drains into the drain pan and out the condensate pipe. When cooling turned off, the air flow should dry the coil fairly quickly unless its super humid. Sure some must get reabsorbed into the air stream but the majority will drain away. If humidity is a problem, it best to keep the AC unit running on cooling.

I've only ever done this in commercial systems but you can put the AC system on cooling to dry the air, then reheat the room or supply air with electric heating to get back to a comfortable temperature.

Maybe I need to do some proper testing. I just remember the few times I did it, my humidity sensor in my room spiked massively and the air coming out of the intake was super musty.

Edit: Maybe my drain isn't working very well?

tweake

2647 posts

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#3433401 11-Nov-2025 15:31

mrhaboobi:

Hi

Yes if you use this as an example diagram, you can see the lossnay with the Red Return , that's the default approach, it feeds into the aircon. you can see the two Orange bypass vents, i would put a damper on that line so that it is open or closed depending on aircon running, essentially it allows air to bypass

i asked BDT about this and they were not in favour

"We wouldn’t recommend this setup, as it can easily cause backflow, pressure imbalance, or even block the airflow of the AC unit, which is not safe."

I'm unclear how those would occur with a electronic damper, ( unless the damper failed? ). Interested in other peoples thoughts on this.. but this is how you could reuse the vents and achieve a bypass. Its somewhat dependant on the Baffle i guess you have set up, do you have a small number of main lines that you could tap into to reduce the number of electronic baffles and Y connectors :) But im a layman so i know nothing in this space so take with a grain of salt.

the problem with the bypass is it will probably backfeed the heat pump and go back through the return filter. to stop that happening is to fit dampers big blue outlets so they shut when the bypass opens. ie red ducts and blue outlet close and orange opens.

tweake

2647 posts

Uber Geek
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#3433403 11-Nov-2025 15:36

AlDrag:

Also, shouldn't the ERV/HRV intake/outtake be on the same side of the house for pressure balance reasons? Due to wind etc? Not sure how important that is in practice, but supposedly a thing?

pressures not really an issue unless you have a super super airtight house and you won't have one of those unless you deliberately make one. plus having inlet and outlet on the same side can cause exhaust air to be sucked back in again.

tweake

2647 posts

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#3433406 11-Nov-2025 15:42

mrhaboobi:

Sounds like you've had a hell of a ride here. Im about to go down the same pathway in chch, HRV/ERV , Ducted etc. Not even sure where i have landed based on your thread. BDT suggests the ERV is the better options for chch

"The ERV core in the LGH-35RVX3 recovers both heat and moisture (sensible and latent heat), while the HRV ( VL350 ) only recovers heat. Since Christchurch has a relatively dry climate, especially in winter, using an ERV helps maintain indoor humidity and prevents the air from becoming too dry. Therefore, LGH-35RVX3 is generally the better choice for this project."

looks like my post has gone awol.

but short version, HRV core ok if the outdoor humidity is good. ERV keeps indoor moisture in and outdoor moisture out, so its best for dry climates or humid climates. however you really need whole house dehumidifier (or at the very least a gauge to warn you if it gets to humid).

also be aware of the sales pitches, as many of these threads on here can attest to.

AlDrag

280 posts

Ultimate Geek
+1 received by user: 27

#3433412 11-Nov-2025 16:09

tweake:

pressures not really an issue unless you have a super super airtight house and you won't have one of those unless you deliberately make one. plus having inlet and outlet on the same side can cause exhaust air to be sucked back in again.

Right. I only have maybe a 2m gap between my ERV intake/outtake, so that motivates me to possibly move my outtake to the other side of the attic, but would be a super long duct haha.

There's still a problem with pressure differences in rooms if I don't want attic air in my house though? e.g. positive pressure in my bedroom, negative pressure in the bathroom, pulls in attic air from my heatlight vents (it vents open in the attic, I assume this is normal for heating? Idk...or maybe necessary for the bathroom extraction fan).

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tweake

2647 posts

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#3433421 11-Nov-2025 16:39

AlDrag:

Right. I only have maybe a 2m gap between my ERV intake/outtake, so that motivates me to possibly move my outtake to the other side of the attic, but would be a super long duct haha.

There's still a problem with pressure differences in rooms if I don't want attic air in my house though? e.g. positive pressure in my bedroom, negative pressure in the bathroom, pulls in attic air from my heatlight vents (it vents open in the attic, I assume this is normal for heating? Idk...or maybe necessary for the bathroom extraction fan).

thats a good example of why nz houses are not airtight. imho i would change the light setup. find one that doesn't vent. normally people don't use showers long enough to create large negative pressure and theres usually leakage around the door. range hoods are usually the big problem. put a roast on etc, eg cook for 4hrs+ with fan running. that can really depressurize the house and pull hot air in from the ceiling.

did you end up getting the controller sorted so you can adjust the ventilation?

AlDrag

280 posts

Ultimate Geek
+1 received by user: 27

#3433553 11-Nov-2025 22:06

tweake:

thats a good example of why nz houses are not airtight. imho i would change the light setup. find one that doesn't vent. normally people don't use showers long enough to create large negative pressure and theres usually leakage around the door. range hoods are usually the big problem. put a roast on etc, eg cook for 4hrs+ with fan running. that can really depressurize the house and pull hot air in from the ceiling.

did you end up getting the controller sorted so you can adjust the ventilation?

Yep, when I saw that in my house, it made me realise how right you are about new houses not being airtight in NZ.
Luckily the range hood in our house only runs for like 30 mins at the most when cooking dinner. I could look into changing the lights or perhaps just sealing it up.

I ended up getting a PAR controller for the heatpump and a wifi controller for the lossnay (the wifi controller was cheap second hand and wanted to adjust lossnay settings with home assistant).

So the Lossnay was running at full fan speed the entire time! I found out with my PAR controller, that the heatpump was configured to high lossnay fan speed. That was an easy fix, now by default it runs at the lowest fan speed. However, whenever the power cuts out (which has annoyingly happened like 4 times in the last 6 months), the default lossnay fan setting resets itself...probably a way to solve this, I just need to read the manual.
I increased static pressure of the heatpump unit to 100Pa from the default 50Pa. I think it's made a big difference. It's definitely not as good as my office aircon, but that's to be expected I guess. The main problem is just the upstairs of our house gets so hot passively from the sun. Big windows and no eaves/awnings will do that I guess.

tweake

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#3433793 12-Nov-2025 15:42

AlDrag:

Yep, when I saw that in my house, it made me realise how right you are about new houses not being airtight in NZ.
Luckily the range hood in our house only runs for like 30 mins at the most when cooking dinner. I could look into changing the lights or perhaps just sealing it up.

I ended up getting a PAR controller for the heatpump and a wifi controller for the lossnay (the wifi controller was cheap second hand and wanted to adjust lossnay settings with home assistant).

So the Lossnay was running at full fan speed the entire time! I found out with my PAR controller, that the heatpump was configured to high lossnay fan speed. That was an easy fix, now by default it runs at the lowest fan speed. However, whenever the power cuts out (which has annoyingly happened like 4 times in the last 6 months), the default lossnay fan setting resets itself...probably a way to solve this, I just need to read the manual.
I increased static pressure of the heatpump unit to 100Pa from the default 50Pa. I think it's made a big difference. It's definitely not as good as my office aircon, but that's to be expected I guess. The main problem is just the upstairs of our house gets so hot passively from the sun. Big windows and no eaves/awnings will do that I guess.

vented lights is done to cool it. so blocking vents is not advised. you would need to change to something else.

back in the day when all downlights where vented, you could turn the lights on and it would light up the ceiling. i can't imagen how much heating would be pouring out those.

check the manual, i can't remember it. i think you need the wired in controller to set the settings. you might be able to do it with original wifi controller. i think its the earlier model which you could set via the dip switches. imho having to have a controller is antiquated. ventilation should be continuous therefore no need for a controller. there is other makes out there that don't controllers.

if i remember right the heat pump only tells the lossnay to turn on/off. then the lossnay runs at its own settings.

don't get me started on kiwi house design. but yes kiwis homes are not designed for cooling because there is no legal requirement for it. plus there is still the old "large north facing windows" that people still incorrectly believe.

but glad your making headway with it.

AlDrag

280 posts

Ultimate Geek
+1 received by user: 27

#3436843 22-Nov-2025 22:25

Welp, pretty sure the reason for most of my woes is due to my unit being underspec'd! They installed a 5kw (cooling) Mitsubishi PEAD50 for me last year.
Today, Auckland was decently hot, and my unit just couldn't cool a single room to set point upstairs, not even close! What doesn't help is that my house (built last year) has no awnings and eaves and big windows, so it can store a lot of heat.

When I talked to my neighbours today, some with a smaller home, some with the exact same one, they all have 7kw (cooling) units! I suspect in my case, my return is too far away, the poor airflow is getting heated too fast before it reaches the return and my unit then just can't keep up.
Even with Lossnay turned off, but maybe the Lossnay ducting that integrates with my return ducting etc, still interferes in some way.

Here's an example of my son's room today. As you can see, even after sunset, the room takes a long time to get down to set point (21 degrees). But during the day, it has no chance.

I guess I will just contact my installer that my unit is under performing and suspect maybe it's not big enough and what my options are. Could also be the loss of airflow from the ducting work, but I assume raising the static pressure would have accounted for that.

timmmay

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#3436914 23-Nov-2025 07:57

Ducted systems aren't the fastest in the world. I find the best approach is to turn them on early to stop temperatures going up, rather than turning them on once it gets warm.

triggers:
- trigger: numeric_state
entity_id:
- climate.pa_bedroom
above: 21.4
attribute: current_temperature
conditions:
- condition: time
after: "11:30:00"
before: "16:00:00"
- alias: Month is Oct, Nov, Apr
condition: template
value_template: "{{ now().month in [10, 11, 4] }}"

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AlDrag

280 posts

Ultimate Geek
+1 received by user: 27

#3436915 23-Nov-2025 08:03

timmmay:

Ducted systems aren't the fastest in the world. I find the best approach is to turn them on early to stop temperatures going up, rather than turning them on once it gets warm.

triggers:
- trigger: numeric_state
entity_id:
- climate.pa_bedroom
above: 21.4
attribute: current_temperature
conditions:
- condition: time
after: "11:30:00"
before: "16:00:00"
- alias: Month is Oct, Nov, Apr
condition: template
value_template: "{{ now().month in [10, 11, 4] }}"

Supposedly my neighbours with their bigger units have no problems cooling their place down quickly though. I mean, maybe their units are oversized, 30mins to an hour, that's fine, but yesterday it just wouldn't cool down.

I'll do another test today with better stats, if it gets hot enough (looks like it'll be cloudy).

timmmay

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#3436921 23-Nov-2025 08:47

Even if you can cool the room quickly the thermal mass of everything in the room will take the temperature right back up. Preventing the room heating is more effective for us. I've had a ducted heat pump for 5 odd years and I've tried lots of different approaches.

tweake

2647 posts

Uber Geek
+1 received by user: 1138

#3436962 23-Nov-2025 13:53

AlDrag:

Welp, pretty sure the reason for most of my woes is due to my unit being underspec'd! They installed a 5kw (cooling) Mitsubishi PEAD50 for me last year.
Today, Auckland was decently hot, and my unit just couldn't cool a single room to set point upstairs, not even close! What doesn't help is that my house (built last year) has no awnings and eaves and big windows, so it can store a lot of heat.

When I talked to my neighbours today, some with a smaller home, some with the exact same one, they all have 7kw (cooling) units! I suspect in my case, my return is too far away, the poor airflow is getting heated too fast before it reaches the return and my unit then just can't keep up.
Even with Lossnay turned off, but maybe the Lossnay ducting that integrates with my return ducting etc, still interferes in some way.

Here's an example of my son's room today. As you can see, even after sunset, the room takes a long time to get down to set point (21 degrees). But during the day, it has no chance.

I guess I will just contact my installer that my unit is under performing and suspect maybe it's not big enough and what my options are. Could also be the loss of airflow from the ducting work, but I assume raising the static pressure would have accounted for that.

it doesn't look undersized. looking at that its cooling perfectly well, its just not turning on when its meant to. that may be because of where temp sensors are located compared to where the Mathew temp sensor is. you may have more heat load in that room at that time of day, or not enough airflow through that room (is the door open?).

i assume setpoint is 21c.

i assume you meant "gains a lot of heat" which is typical with nz large windows and no code requirement to factor in heat gain.

tweake

2647 posts

Uber Geek
+1 received by user: 1138

#3436963 23-Nov-2025 13:55

timmmay:

Even if you can cool the room quickly the thermal mass of everything in the room will take the temperature right back up. Preventing the room heating is more effective for us. I've had a ducted heat pump for 5 odd years and I've tried lots of different approaches.

yes. they are meant to run all day. but kiwi low quality housing means normal tactic is to only run after the fact.

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