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2777 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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1846 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.  




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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?




 
 
 
 


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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. 




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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)?


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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. 




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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.


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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.


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