Green Building Forum - Single Room Heat Recovery / Dehumidifier Tue, 19 Dec 2023 08:35:55 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300724#Comment_300724 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300724#Comment_300724 Mon, 13 Mar 2023 22:18:52 +0000 Victorianeco
Not very thermally efficient and as there's 4 of us in a 35m2 area we're noticing the effects of mould/condensation.

It's too cold to open windows and we rely on a air to air heat pump for heating.

The room drops to 12c overnight which is when I think the condensation forms...

Humidity levels are fine in the day at 20c (50% RH).

I need to get some fresh air into the room or a dehumidifier. There is a small bathroom within the area that has an old 'on with light' fan. Would a single room MVHR unit work in the existing hole?

Ideally we want the fresh air in the room/office

The room isn't particularly airtight or insulated so just weighing up options.

As the employer I know I have a duty of care to my team but surely the landlord does too?

Thoughts on the best solution?]]> Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300725#Comment_300725 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300725#Comment_300725 Mon, 13 Mar 2023 22:42:15 +0000 borpin https://www.amazon.co.uk/dp/B086YYL439 then I'd probably just get a dehumidifier and run it overnight. I bought one of these for a student flat and it has worked wonders. https://www.amazon.co.uk/Meaco-Portable-Dehumidifier-DD8L-EXCLUSIVE/dp/B077T4QPTZ/. Downside is, you might find the humidity drops too low during the day. In which case your only solution is to maintain a higher temperature overnight.

Fresh air might not help. It is the warm moist air from the day (folk sweating) that condenses overnight. The outside air might actually have more moisture in it.]]> Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300726#Comment_300726 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300726#Comment_300726 Tue, 14 Mar 2023 09:01:01 +0000 fostertom Make sure any dehumidifier is the desiccant type (like borpin's Meaco) not the old refrigerant type, which are fine in the moist tropics but v inefficient further north.]]> Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300727#Comment_300727 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300727#Comment_300727 Tue, 14 Mar 2023 09:06:57 +0000 WillInAberdeen
If it's 20⁰C/50%RH in the day, then when it drops to 12⁰C it will be 80%RH which is bit too high (lots of psychrometric calculator widgets online).

At this time of year, even when it is chucking down rain and snow outside, the cool outside air contains much less moisture than the warmer indoors air. That is why ventilation is so effective now and ventilation systems can be turned right down to low flow rate. Different in high summer, but then the room won't get cooled overnight and you can open windows.

As a workplace, you probably need to have plenty ventilation (eg avoid sharing germs and everyone goes off sick).]]> Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300728#Comment_300728 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300728#Comment_300728 Tue, 14 Mar 2023 11:01:53 +0000 djh
"HSE's Approved Code of Practice and guidance (PDF) states that 'The fresh-air supply rate should not normally fall below 5 to 8 litres per second, per occupant.' A value of 10 litres per second per person is recommended in some building guides as a suitable value for most commercial buildings."

So 4 people is up to 140 m³/hr. I think that's more than domestic single room MVHR units do.

See also HSE guide:
Workplace health, safety
and welfare
Workplace (Health, Safety and Welfare) Regulations 1992
Approved Code of Practice and guidance]]> Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300732#Comment_300732 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300732#Comment_300732 Tue, 14 Mar 2023 11:36:45 +0000 WillInAberdeen
in VE's case that's about 1-2 ACH during weekday hours.

From the description of the factory, and the very acceptable %RH measured during the day, it wouldn't be surprising if there is already more ACH happening than that, due to air leakages, and people coming/going through doors.

Sounds like the problem is more at night when the temperature drops off (what about over the weekend?).]]> Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300734#Comment_300734 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300734#Comment_300734 Tue, 14 Mar 2023 12:00:40 +0000 borpin Posted By: djhThe humidity is just a symptom of lack of fresh air.I'd disagree with that. It *might* be, but the air outside could contain more moisture than inside. 50% RH during the day is a good value to have.

Temperature is the most likely cause.

Test for CO2 to confirm what the air quality is like.]]> Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300742#Comment_300742 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300742#Comment_300742 Tue, 14 Mar 2023 19:50:08 +0000 djh Posted By: borpinTest for CO2 to confirm what the air quality is like.I agree with this.]]> Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300746#Comment_300746 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300746#Comment_300746 Tue, 14 Mar 2023 20:42:02 +0000 Jonti Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300748#Comment_300748 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300748#Comment_300748 Wed, 15 Mar 2023 00:14:51 +0000 Victorianeco
I don't think fresh air is an issue either, I have access to several dehumidifiers. I think the issue is of the dewpoint. This appears to condense on the 4" cold main running through our office space. As this is the coldest point in the room this is why.

Could insulate it but I think the condensation will then go elsewhere. It is the black mould that is a concern]]> Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300749#Comment_300749 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300749#Comment_300749 Wed, 15 Mar 2023 07:38:23 +0000 borpin Posted By: VictorianecoWill, how can relative humidity change? The whole point it is relative....Yes exactly. Relative to the maximum water vapour the air can hold. That maximum drops as the air cools so the relative value rises. Good chart here https://manual.museum.wa.gov.au/book/export/html/89

Get a temp/humidity sensor and measure - you cannot beat data.


Posted By: VictorianecoIt is the black mould that is a concern
Need to deal with the cause first.]]> Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300750#Comment_300750 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300750#Comment_300750 Wed, 15 Mar 2023 09:08:16 +0000 WillInAberdeen Posted By: VictorianecoWill, how can relative humidity change? The whole point it is relative....

The relative humidity (%} changes when the air cools down overnight. The absolute humidity (grammes of water) stays the same.

For example, your room during the day would have a capacity to carry up to 17 grammes of water in each m³ of air before it hits it's dewpoint. You measured that it is only using up 50% of its max capacity, so that's 50% of 17 = 8.5g per m³ of actual humidity is floating around the room.

Overnight, it"s still got the same actual humidity floating in it, 8.5g/m³. However it's cooler so it has much less capacity to carry water, the max capacity limit is reduced to 11g/m³. So it's creeping much closer (8.5/11= 80%), relative to its new dewpoint limit.

You don't want it to be that close to hitting its dewpoint limit because mould can grow. So either keep it warmer, or replace it with air from outdoors which is drier (less actual grammes of humidity) at this time of year than your room is.

Together, your team breathe out several kilogrammes of humidity during each work day. If you wipe up what condensed on the pipe and weigh it, it will only account for a tiny bit of those kilogrammes. The rest is going somewhere else - either condensing on unseen surfaces somewhere (bad) or being ventilated away (good). You likely only need to top up the ventilation a little, to get rid of the rest of the water that you're all breathing out, a continuous-running bathroom fan mhrv might be enough. If its not, then at least it's a cheap first step.

(Do you have a kettle, or hang up wet site jackets? Could be quick win to move that stuff somewhere else.)]]> Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300753#Comment_300753 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300753#Comment_300753 Wed, 15 Mar 2023 11:32:35 +0000 djh Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300756#Comment_300756 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300756#Comment_300756 Wed, 15 Mar 2023 15:13:30 +0000 WillInAberdeen
Walls and floors have much bigger surface areas, so are more useful for thermal inertia.

(Edit to add: offices are occupied for about a quarter of the hours in the year, so is good to have a setback temperature by a few ⁰ the rest of the time, so low thermal inertia helps with that. But a large area of hygroscopic materials would help stabilise the RH overnight - maybe a pile of straw bales? :bigsmile: )]]> Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300800#Comment_300800 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300800#Comment_300800 Sat, 18 Mar 2023 17:24:26 +0000 Victorianeco
Any recommendations on a single unit for a starter unit to go in the bathroom? I'm still not sure how that would ventilator the main office space though as the site exchange will be in the bathroom not in the main office space though...]]> Single Room Heat Recovery / Dehumidifier http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300803#Comment_300803 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17776&Focus=300803#Comment_300803 Sat, 18 Mar 2023 18:36:24 +0000 cjard