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2 X Midea 16kw setup

Air Source Heat Pumps (ASHPs)

Last Post by HughF 3 years ago

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Mookyfoo

(@mookyfoo)

Trusted Member Member

Joined: 3 years ago

Posts: 27

Topic starter 29/06/2022 10:02 pm

Hi guys, just wanted some input from you on my system now that the installation is all but complete so I can now describe how its been setup.

We have 2 Midea 16kw ASHP connected as shown below.

There are 2 manifolds as shown below and radiators upstairs.

The ASHP (1) that does DHW and the upstairs radiators is set to use the temperature compensation curve as set out in the Freedom setup guide.

The ASHP (2) that does the UFH is set to have a fixed flow temp of 35 degrees.

ASHP 1 therefore can vary its water temp between 37 and 55 degrees depending on outside temp.

However ASHP 2 is fixed at 35 degrees.

As the 2 ASHP’s share the buffer tank this means there could be conflicts in temperature.

For example if ASHP 1 is outputting water at 50 degrees to the radiators and then ASHP 2 gets a call for heat it will see that the water in the buffer is already above its fixed temp and therefore contribute no heat, but also allow 50 degree water to go through the UFH which exceeds most flooring max temps as there is no mixer/blender at the manifolds.

The above is only one example of where there could be issues and conflicts between the 2 ASHP’s I’m sure there are others and its likely that the hours in operation are not likely to be spread evenly over the 2 units..

As the ASHP’s aren’t connected (master/slave) there is no way for them to communicate and work together.

In my mind the best solution is to have them both connected together (Master /Slave, I believe this is possible) running temperature compensation or fixed temp and have a mixer on each manifold limiting the UFH water temp to around 30 degrees.

I assume FreedomHP had input only about the ASHP's and probably didnt specify anything about the manifolds.

I'm about to send the above to my installer, I did raise my concern about no mixers and the possibilty of different temps in the buffer and at the manifolds but they didnt see it as a problem when I brought it up some time ago and until the setup was complete I couldnt be sure if they were right or wrong.

I'd be interested if anyone else has a dual ASHP Midea system especially if its been setup as master and slave.

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HughF

(@hughf)

Noble Member Member

Joined: 3 years ago

Posts: 489

30/06/2022 7:48 am

Who was your system designer, just so I know who to avoid 🙂

That ufh manifold needs a mixer, I genuinely don’t get why these installers think otherwise. Or better yet mixed pump group with a esbe mixer for weather comp’d ufh.

What size of property needs that much heat input? I’d be interested to see your heat loss calcs. Although to be fair, a 16kW midea is more like a 12 in normal winter conditions.

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

👍

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Mookyfoo

(@mookyfoo)

Trusted Member Member

Joined: 3 years ago

Posts: 27

Topic starter 30/06/2022 6:52 pm

To be fair I think its a steep learning curve for the installer and probably themselves and Freedom probably havent given each other the full picture of the install, and every one seems to have its difficulties, especially in our case being a retro fit to a house that was previously storage heaters. Anyway the installer is has been in conversation with them and its agreed they will fit mixers on the manifolds. As to cascading the heat pumps (master/slave) they feel there is little to gain as they dont think they are as intelligent as we might think in terms of sharing out the work load, but I could try this later on if I feel there might be something to gain.

As for the calcs, not really looked too closely into them other than it was felt one 16kw (probably nearer 12kw as you say) was borderline and therefore the installer didnt want cut it fine and I simply want to heat the house properly (unlike what the storage heaters were doing). The belief is the ASHP doing upstairs and DHW is likely to spend most of its running time doing the DHW and on the odd occasion some heating.

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HughF

(@hughf)

Noble Member Member

Joined: 3 years ago

Posts: 489

02/07/2022 8:58 am

Take the buffer out, split the two systems into upstairs and downstairs. Set the weather comp curves for the upstairs rads to suit, and the same for the downstairs.

They’ll never work well driving into a common buffer.

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

👍

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