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Paul1977

3427 posts

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#257269 23-Sep-2019 11:45
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Related to my other post, I'm hoping for some feedback from more knowledgeable people regarding how these integrate together.

 

I've drawn a couple of diagrams to get my head around it.

 

If my understanding is the correct, the 'official' way to do it is with illustrated in the below diagram:

 

Click to see full size

 

This seems like it would require more ducting as the heat pump and Lossnay each have their own return ducting, and it looks like if you wanted to run the Lossnay without heating or cooling you would be required to run the heat pump in fan mode?

 

 

 

At least one installer I've spoken to has recommended the following:

 

Click to see full size

 

This method would seem to allow for the heat pump and Lossnay to use the same return vents as each other, and would allow you to run the Lossnay while the heat pump is turned off. This seems like a better configuration, or am I missing something?

 

Am I understanding these methods correctly, and are there others ways to do it?





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Disrespective
1852 posts

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  #2323445 23-Sep-2019 16:17
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Most of the full-fat heat recovery systems (Zehnder etc) that i've specified for installation assume that the recovery system is considered the primary means of ventilation. If there is a heatpump/heater element installed, then this is for supplementary heating. This would be like the first image but without using a heatpump return plenum, just one for the Lossnay. As drawn there will be a mixture of returned stale air and returned fresh air being present in the return plenum before being heated/cooled and sent around the house. 

 

This first image assumes the heatpump is the primary means of pushing air and determines whether extra heating/cooling is required before it being sent around your home. 

 

I would be trying to get the return vents all going into the Lossnay system first, and then into the heatpump. The heatpump can then choose to add/remove heat from the fresh air as required before being distributed to the vents around your home. 

 

Bear in mind that I have no experience with a Lossnay system, nor have I read all the tech docs about how it works, so could very well be missing something obvious as to why it would want to mix stale and fresh air.  


Paul1977

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  #2323657 24-Sep-2019 07:45
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Thanks @Disrespective

I assume the reason it’s mixing fresh and recycled air is because the heat pump can move up to 700 l/s of air, where the Lossnay maxes out at 139 l/s.

But I am having trouble getting my head around it.

Do any Geekzoners have a ducted heat pump and Lossnay (or a comparable Daiken setup) that they could share their experiences?




 
 
 
 


Disrespective
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  #2323678 24-Sep-2019 08:25
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How new is your house out of interest? If it's of an older pre-1960's construction type then it might be getting quite a few ach (air changes per hour) passively. If this is the case then there is limited benefit of any heat exchange system. 

 

I believe the general rule of thumb is for the infiltration rate (passive ach) to not exceed 10-20% of the flow rate through the heat recovery unit. 

 

/* Start napkin maths

 

If we take your 139l/s for the Lossnay then work with 15% (a mid point between 10-20%) we get ~20L/s or 7200L/hr for the max infiltration rate that should be occurring passively.

 

Then take an approx. house volume of 405m3 or 405,000L (15m Wide x 10m Long x2.7m High) we can divide 405,000L volume by the 72,000L/Hr then we're at a ach value of 0.178ach. e.g. Your house needs to be more airtight than a simple 2005+ construction method to make having the Lossnay worthwhile. 

 

*/ End napkin maths

 

See https://alf.branz.co.nz/manual/understanding-alf-calculations/ventilation/ or use the ALF tool yourself to calculate a more accurate ach value for your house.

 

I used to have a Daikin split ducted system at my old house in Wellington and aside from hating the 'smart' control features it was a pretty good system. I'd recommend having a really good think about where the ducting goes to prevent losses along their lengths. I believe that done poorly you can lose anywhere up to 40% of the efficiency of the system. Ideally they are within the insulated envelope and/or kept to as short lengths as possible. 


Paul1977

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  #2323703 24-Sep-2019 09:16
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@Disrespective We are looking at the ducted heat pump and Lossnay for a new build. I don't think there's anything complex about the design (but I don't know what qualifies as complex) so I guess base airtightness of 0.15 ac/h based on that Branz table you linke?

 

I hate to admit it, but your napkin maths has lost me a bit as to why the Lossnay wouldn't be worthwhile unless the house was more airtight that a simple 2005+ construction?

 

The page you linked says "An appropriately ventilated home has a local air leakage rate of between 0.35 - 0.50 ac/h. A value below this is overly airtight and will require additional ventilation". Wouldn't this suggest that any new home would benefit from an active ventilation system?

 

At 0.15 ac/h isn't a simple 2005+ construction getting less that half the recommended ventilation (without adding mechanical ventilation or opening windows)?


Disrespective
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  #2323719 24-Sep-2019 09:50
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Complex is a term that is pretty loose but generally if there are more than 8 internal and external corners then i'd consider it complex. e.g. a 'T' shaped house would be simple if the roof was also simple, but a 'H' shaped house would be considered complex in form. 

 

If the home is overly airtight then you will need to open a lot of windows for passive ventilation, or an active ventilation system like the Lossnay to ensure the air you're breathing inside is free of dust and other pollutants.

 

I would absolutely recommend a heat recovery system to all newly built homes that are above the baseline set in the building code. What I mean by that is that they use square stopped gib ceilings with IC rated lighting which can be covered by insulation, and mid/high spec joinery with good weather seals. That said i'd still say that the heat recovery system should be the primary ventilation system and the heatpump a secondary booster. 

 

If the house is already 'leaking' air (even with the windows closed) then adding another active ventilation system is just going to compete with the natural ventilation. The argument is that if your active ventilation system is undersized, or the house leaks too much air passively, then the efficiency of the system is degraded to a point where you may as well just heat the rooms normally. 

 

Either way it sounds like your new house will benefit from it so all of the above is probably moot and your question of how to run the ducting still stands. And I am happy to wait for someone more knowledgeable than me to answer that one. 


Paul1977

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  #2323726 24-Sep-2019 10:01
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Disrespective:

 

Complex is a term that is pretty loose but generally if there are more than 8 internal and external corners then i'd consider it complex. e.g. a 'T' shaped house would be simple if the roof was also simple, but a 'H' shaped house would be considered complex in form. 

 

If the home is overly airtight then you will need to open a lot of windows for passive ventilation, or an active ventilation system like the Lossnay to ensure the air you're breathing inside is free of dust and other pollutants.

 

I would absolutely recommend a heat recovery system to all newly built homes that are above the baseline set in the building code. What I mean by that is that they use square stopped gib ceilings with IC rated lighting which can be covered by insulation, and mid/high spec joinery with good weather seals. That said i'd still say that the heat recovery system should be the primary ventilation system and the heatpump a secondary booster. 

 

If the house is already 'leaking' air (even with the windows closed) then adding another active ventilation system is just going to compete with the natural ventilation. The argument is that if your active ventilation system is undersized, or the house leaks too much air passively, then the efficiency of the system is degraded to a point where you may as well just heat the rooms normally. 

 

Either way it sounds like your new house will benefit from it so all of the above is probably moot and your question of how to run the ducting still stands. And I am happy to wait for someone more knowledgeable than me to answer that one. 

 

 

Thanks @Disrespective, I appreciate you knowledge on this.


timmmay
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  #2323728 24-Sep-2019 10:01
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Even with an older "leaking" house, if the options are heat recovery ventilation vs forced outside air, are there enough benefits to bother with HRV? My assumption is that it's probably better as instead of pushing in cold air you push in pre-warmed air.

 

I guess it's probably pretty difficult to quantify passive air exchange in an existing house.


 
 
 
 


cst555
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  #2479844 9-May-2020 17:38
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https://www.passivhaustrust.org.uk/guidance_detail.php?gId=46

There is some new research by PassivHaus Trust in UK about MVHR being beneficial even with conventional buildings.

cst555
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  #2479871 9-May-2020 18:24
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https://www.mitsubishi-electric.co.nz/ventilation/solution.aspx

Simple explanation of the Mitsubishi system with Lossnay and Ducted heat pump.

The humid rooms (kitchen, bathrooms, possibly laundry room) should all be extracted through the Lossnay system so that the highly humid air is not recirculated. It looks like there is an intake for the ducted heat pump in the hallway which would allow the heat pump to get the extra airflow it may require above what the Lossnay can deliver alone.

It is worth noting that Lossnay is Energy Recovery Ventilation (ERV), which tends to have a lower efficiency than an equivalent Heat Recovery version - everything else being the same. For example Zehnder Q350 (high end) offer both HRV (90% efficient) and ERV (85% efficient) exchangers.
https://en.m.wikipedia.org/wiki/Energy_recovery_ventilation

Paul1977

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  #2479926 9-May-2020 20:09
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cst555:
The humid rooms (kitchen, bathrooms, possibly laundry room) should all be extracted through the Lossnay system so that the highly humid air is not recirculated.


This depends on the model of Lossnay. Most of them have a paper core, and these are not good for direct extraction from highly humid areas.

I believe only the quite small residential unit has a resin core that is suitable for extraction from bathrooms and other highly humid areas.

We had several quotes, and they pretty much all said for our size house (225m2) the resin core unit was too small. So we are going for a larger unit with a paper core. This just means we still need standard extractors in bathrooms and a normal kitchen rangehood.

Kickinbac
306 posts

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  #2479982 9-May-2020 22:25
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I’d follow Mitsubishi recommended layout, the first option. For the ducted/lossnay integrated system there is only one controller so they work together.

Froglotion
145 posts

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  #2479986 9-May-2020 22:59
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What region are you building in?

 

I put a 16kw Fujitsu in my place, 200sqm of living space. I also put zones in, which is a total luxury and not required, but I quite like it. Timer can be set to heat certain zones and that sort of thing. I did look at the Mitsi Lossnay option too, but don't recall why I didn't go for it in the end. I think at the time Mitsi maybe didn't do zoning. I wouldn't stray from how the system is designed to be run personally. Lossnay on it's only may not be effective in a house your size. Whereas the heatpump fan will have zero issues ventilating the house. Mine is on low fan 90% of the time, when running. It runs in morning for 1-2 hours and then it's turned on as required after work. Haven't had any moisture problems at all. 


Dingbatt
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  #2480086 10-May-2020 08:41
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Just looking at the diagrams you initially posted from a airflow perspective (ignoring heat transfer, etc). In the second diagram you would have the fans in the respective systems fighting each other. The lossnay fans are trying to pull air from the low pressure side of the heat pump fan and return it to the high pressure side. Because these are low pressure, high volume fans, it could lead to surging.

 

This is not the case in the first diagram as the lossnay draws from ambient and returns to low pressure side of the heat pump. The air being returned to the inlet plenum may end up flowing ‘the wrong way’ if the heat pump fan isn’t running.





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Paul1977

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  #2480099 10-May-2020 09:22
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Dingbatt:

 

Just looking at the diagrams you initially posted from a airflow perspective (ignoring heat transfer, etc). In the second diagram you would have the fans in the respective systems fighting each other. The lossnay fans are trying to pull air from the low pressure side of the heat pump fan and return it to the high pressure side. Because these are low pressure, high volume fans, it could lead to surging.

 

This is not the case in the first diagram as the lossnay draws from ambient and returns to low pressure side of the heat pump. The air being returned to the inlet plenum may end up flowing ‘the wrong way’ if the heat pump fan isn’t running.

 

 

The way they are meant to run is that the heat pump fan is always running if the Lossnay is running, even of not actively heating or cooling. The second diagram was one installers way to allow you to run the Lossnay with the heat pump turned off, but is not how they are designed to work so did not go with that approach.

 

In the end we are having ours configured as per the below diagram. The heatpump and lossnay each share the two return vents, but use Y branches in the ducting so some air goes back to the Lossnay and some goes back to the heat pump.

 

We've also upgrade to R1.0 ducting from the stand R0.6

 

The Lossnay will also have the summer bypass which always you to bring in fresh air but bypass the heat exchanger if you wish.

 

We are zoning with an Airtouch 4 system which makes each room it's own zone. Each zone has a wireless temperature sensor. The electronic baffles for each zone open and close in 5% increments which allows the system very fine control of the temperature in each zone. As with any zoned heat pump you, of course, can't heat one zone while cooling another.

 

It's not shown in the diagram, but we are also having a small return vent in the media room as well. This room will have the door the shut while in use, and an undercut or vented door was not a good option when attempting to control light and sound in the room.

 


Froglotion
145 posts

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  #2480684 10-May-2020 17:03
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I either turn the media room zone off or shut the door if i'm in there. Even on low flow, the airflow is slightly audible. It doesn't annoy me at that level, but being an insulated room, the temperature isn't usually an issue. Return vent is a good idea though, lets you have both options if you wish.


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