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dazdaz

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#315013 7-Jun-2024 12:20
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Hi Guys,

 

 

 

I have a Mitsi pead M71, 417 L second air flow. Its a big house and this unit is just for the 5 bedrooms, 4 bedrooms have 200mm ducting and outlet, the master bedroom, 250mm ducting and outlet. Only two of us living in the house so the Master bedroom is the predominant room to be cooled and heated. Trying to save on power, rather than having other rooms open as spill zones, I am considering a bypass vent so the air is not wasted inside the house. Would anyone have any experience on what size bypass damper should be used for this size heatpump?

 

 

 

Cheers


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timmmay
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  #3245721 7-Jun-2024 13:46
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Do you have an installer doing this for you? If so they should be able to work this out.

I have Airtouch 4. I can see than the damper closes to 5% as rooms get up to heat, leaving 95% of the air that could spill. If your 250mm duct can carry all the air to your master bedroom it's probably sufficient to carry the spill. If anything I would go larger, similar to the duct size between the return vent and the ceiling unit.

I'm not at all qualified to give advice in this area 😁



dazdaz

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  #3245725 7-Jun-2024 14:07
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Thanks for the reply.

 

 

 

Yes, the install is half way done. The installer should be back in the next week or so to complete the job, I have not spoken to him regarding a bypass but thought id get a heads up on it first.

 

The return vent has a 400mm ducting, I think that would be way over size for the bypass, given the unit should be on a lower fan speed when I only have one room heating.

 

 

 

Cheers


timmmay
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  #3245733 7-Jun-2024 14:17
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True. 250mm might be enough, maybe you go a size up for safety. The installer should know.

I wish I knew about bypass zones when mine was being installed. Instead I have a bunch of home assistant automations messing with damper positions to prevent excessive spill.



dazdaz

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  #3245736 7-Jun-2024 14:37
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I have installed all the ducting, vents, etc etc myself to save a bit of money, I didn't know about the bypass until researching the system the other day, initially I will try it without, then most likely ill buy the required parts to install a bypass.

 

 

 

If I had known about the bypass beforehand I probably would have had extra ports put on the manifolds.

 

 

 

Cheers


dazdaz

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  #3245748 7-Jun-2024 15:01
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Looking at the air volume for the three fan speeds of the Mitsubishi PEAD-M71, I am surprised by the minimal difference between low and high settings: 292 L/S for low, 350 L/S for medium, and 417 L/S for high. I had expected the low setting to be around 150 L/S. The specification also mentions "0-417" for high, which is confusing. It almost sounds like high is an auto setting, though these PEAD models don't actually have an auto fan speed option. 

 

I had hoped the AirTouch 5 could manage the fan speeds with its own auto setting. However, from what I've read, it appears that the AirTouch 5 will only operate according to the factory-set Mitsubishi fan settings.


timmmay
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  #3245756 7-Jun-2024 15:43
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I have a Daikin 10kw ducted, airflow numbers L/M/H are 383 / 458 / 533. Both your mitsi and my Daikin have 1.4X more airflow on high than low. It feels like a bigger difference though. I don't know anything about Mitsubishi other than they're good quality. Airtouch 4 only uses the Daikin fan settings.

 

Yeah I'd have added bypass but getting the manifold made is too much hassle. You could try using Home Assistant to automate things, I can give you some pointers. You can have the spill zone set to wherever you like, your master bedroom if you like, but it will get a bit hotter than you prefer. Airtouch 4 tends to turn the damper down from 100% well before it's up to heat. One of my automations watches for when that happens, when it's not up to heat and closing the damper, and opening it back up. Another detects when the damper is only slightly open and opens it more to avoid overheating the spill zone. It does other things too, basic on / off / temperature / zone control, I have 172 automations but that's across three heat pumps, a bit of lighting, ventilation, blinds, phone, etc.

 

I wrote a guide with my Airtouch / ducted experiences here, if you're interested. You might pick up a couple of things, like vents.


dazdaz

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  #3245759 7-Jun-2024 15:50
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I would just install T's in the lines for the bypass damper to link into.

 

 

 

I have no knowledge of home assistant, will this communicate with Airtouch and the heatpump and allow you to over ride them with your own setting preferences?


 
 
 

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timmmay
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  #3245768 7-Jun-2024 16:16
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dazdaz:

 

I would just install T's in the lines for the bypass damper to link into.

 

I have no knowledge of home assistant, will this communicate with Airtouch and the heatpump and allow you to over ride them with your own setting preferences?

 

 

I guess you could do it that way. Best ask your installer if it's a good idea. I have no idea.

 

Home Assistant is an open source project that lets you control and automate many of the things in your home, like heat pumps, lights, blinds, anything with a network interface really. I started using it a few years ago. Airtouch has an API which Home Assistant communicates with. So instead of one app for each appliance you have one app to rule them all. There's a steep learning curve, but there's heaps of youtube videos to get you started. I started using it because my Airtouch 4 didn't have enough timers for me, and didn't let me change the mode (heat / cool / air).


Handle9
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  #3246229 8-Jun-2024 16:05
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dazdaz:

 

Looking at the air volume for the three fan speeds of the Mitsubishi PEAD-M71, I am surprised by the minimal difference between low and high settings: 292 L/S for low, 350 L/S for medium, and 417 L/S for high. I had expected the low setting to be around 150 L/S. 

 

 

You'd freeze the coil at 150 l/s. You can't beat physics.


dazdaz

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  #3246774 10-Jun-2024 08:14
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Handle9:

 

dazdaz:

 

Looking at the air volume for the three fan speeds of the Mitsubishi PEAD-M71, I am surprised by the minimal difference between low and high settings: 292 L/S for low, 350 L/S for medium, and 417 L/S for high. I had expected the low setting to be around 150 L/S. 

 

 

You'd freeze the coil at 150 l/s. You can't beat physics.

 

 

 

 

If that is the case I would have thought the same would happen with a bypass installed, if the unit is circulating cold air passed the coil, its going to get pretty cold.


timmmay
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  #3246775 10-Jun-2024 08:17
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I assume heat pumps have sensor everywhere and can protect themselves against common things like input temperature begin higher or lower than expected.

dazdaz

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  #3246777 10-Jun-2024 08:25
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I have been doing a bit of reading on HVAC forums, and it seems the consensus is that to size the bypass should equal the total airflow of the unit minus the smallest zones airflow capability. So it would seem a 300mm damper should be the correct size for my bypass.

 

 

 

I wonder where the bypass damper should plug into? there is nothing in the manual that states if a zone or what zone should be used. (yes I know I should talk to my installer, but I wont be seeing him until the end of the week and I like to have all of this making sense to me beforehand)


timmmay
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  #3246801 10-Jun-2024 09:03
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My understanding is that the bypass is a zone, it needs its own damper. It is simply a loop from the output of the heat pump back to the input. I'm not sure if that is quite what you're asking though.

dazdaz

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  #3246808 10-Jun-2024 09:16
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timmmay: My understanding is that the bypass is a zone, it needs its own damper. It is simply a loop from the output of the heat pump back to the input. I'm not sure if that is quite what you're asking though.

 

If it is a zone then it sounds like it will just occupy one of the 8 zones. I saw a diagram somewhere online a while ago that showed the bypass having its own socket to plug into. Maybe the older models have this. 


timmmay
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  #3246812 10-Jun-2024 09:28
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That soundsreasonable. I've never really looked into it in detail, I've just read the air touch 4 manual.

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