Balanced HRV efficiency and heating

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CrazyM

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Topic # 220349 7-Aug-2017 09:50

Hi all,

I have a well sealed 15 year old house with double glazing and good insulation but get considerable condensation around my aluminium joinery as it isnt thermally broken. Heating is currently provided by a 8.4kW heatpump in the main living area which keeps the house warm (but distant bedrooms take ages to heat). Downlights are LED and well sealed.

I am looking into getting a Cleanaire to get fresh air into my house and help with the window condensation issue. Hopefully it will also help with the heat distribution to the far rooms. I plan to have it running constantly at a low speed.

A couple of questions for people with similar balanced HRV systems..

- Do you find that you lose a noticeable amount of heat from the house into the roof space through ducting lengths and heat exchanger efficiency? Ie, in winter is your house noticeably cooler with the system running and do you require additional heating?

- Is there a company who makes a heat pump unit without fans that could be added to the system if I decide I want additional heating/cooling at a later date? Basically like the inline electric heaters you can get

Cheers,

Michael

timmmay

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Reply # 1840402 7-Aug-2017 10:00

I can't answer your questions, but I do have one observation that's somewhat related. This year we kept the heating on from 5am to 10pm every day, and the really cold nights we had it on for a couple of hours in the night. The whole house feels a lot warmer, even though the thermometers register the same. You could try that for a week and see if your bill is much higher. You can check meter readings if you don't have a smart meter and good energy company.

We have a simple ventilation system, which just pulls fresh air in from outside. In winter I run it something like 11am to 3pm, then for 15 minutes a few times in the evening. I don't see much sense pumping in cold air constantly. In summer I run it mornings and evenings, so we don't make the house too hot. I just have a $10 mitre ten timer on the plug that runs it.

I guess that a ventilation system will make your heating bill higher, because you're using it to heat the whole house. 8kw isn't huge for that, even in a modern house. It should reduce condensation a bit, but not completely, as there's always going to be moisture in the air. We have PVC double glazing, the only time we get any condensation is on a night with no ventilation that's super cold outside. Normally we get none. Replacing your windows is probably excessive.

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Jase2985

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Reply # 1840645 7-Aug-2017 16:25

mitsubishi electric lossnay is a balanced HRV system, than can be connected up with a heat pump system from mitsubishi electric. and it allows the whole system to be controlled from one panel.

I am considering this type of system for a new build as it will run just fine without the heatpump being on and you can use the heatpump if you need to heat or cool.

Amosnz

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Reply # 1840688 7-Aug-2017 17:55

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We have a Smartvent Synery balanced HRV installed about 5 years ago

The rule of thumb for R0.8 insulated ducting is 1 deg loss per 3m of ducting, minus the loss from the heat exchanger. Eg: If we start with 28 degree inlet temp, run 6 meters to the heat recovery unit (75% effective for this calculation), then run 9 meters to the outlet, the air temp will be approximately 17 degrees.

We have a woodburner in the lounge (internal source) as our primary heat source. I've always had the opinion that the 'heat transfer' part of the system never worked as well as I'd hoped, but its hard to remember what it was actually like prior to installation now. The ventilation aspect I've always been very impressed with, we had pooling water in a couple of windows that cleared up and never came back.

The 2kw inline heater options is not worth it, they don't heat the air enough to make a difference. More for taking the chill off than heating. The synergy can have a ducted heatpump put in line with it (Smartvent Integra? or something like that).

Aredwood

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Reply # 1840835 7-Aug-2017 22:19

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First of all, get a good humidity sensor and check if you actually do have high indoor humidity or not.

If the window frames are cold enough, you will still get condensation on them no matter how low your indoor humidity is.

As an experiment, leave the range hood and bathroom extractor fans running one evening. (Assuming they are vented to outside) and see if that reduces condensation levels.

CrazyM

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Reply # 1840994 8-Aug-2017 11:44

Thanks Amosnz, that exactly the feedback I was after. The cost of the fresh dry air appears to be a considerable amount of heat, and since I dont have a massive heat source like a fireplace it may be a sideways step.

Jase, I've had a look at the lossnay and I've got a couple of things against it. Apart from the punishing price it uses smaller diameter / higher pressure ducts and its heat exchanger isnt as efficient as a Cleanaire or similar. I would like to go back to a Mitsubishi system though as their heatpumps in my previous house were much better than my current Fujitsu's.

I'll use my workshop humidity sensor and check the indoor readings

timmmay

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Reply # 1840999 8-Aug-2017 11:49

You could consider putting extra insulation around / over the ducting.

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Jase2985

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Reply # 1841011 8-Aug-2017 12:18

There is not a huge deal of difference in efficiency, 82-86% vs upto 95%, doesnt say how low it gets though.

the commercial lossnay units, which match the flow rates of the cleanair units, have larger ducts and lower static pressure