Will using a dehumidifier warm the air and reduce the cold damp feeling in winter?

GValue

I just found this information: 

"What’s the ideal humidity level in a UK home?

The range in which optimal indoor humidity is achieved is, thankfully, quite broad. If you’re getting a reading somewhere between 30 and 60%, you’re in pretty good shape. That being said, it can prove to be tricky to maintain such levels, so constant monitoring is a good idea. This can be done by way of a hygrometer, which can be purchased online for under a tenner.

As one would expect, the changing seasons mean changing humidity levels. The difference, though, is relatively slight. Both winter and summer levels fall within the 30-60% range, with a 10% variation at the appropriate end of the scale:

• Optimal indoor summer humidity levels: 40-60%
• Optimal indoor winter humidity levels: 30-50%

 

Very high readings are considered to be anything above 70% humidity, while low humidity is anything below 25%. These should be addressed regardless of the time of year."

FreeBear

GValue said: Will using a dehumidifier warm the air and reduce the cold damp feeling in winter or is it a false economy?

Used a compressor type dehumidifier in a small box room a few winters back to dry the space after having the walls & ceiling plastered. Couldn't heat the room as the radiator had been removed. Even so, the dehumidifier kept the room nice & toasty - Wouldn't want to use one as a primary source of heating though.

Scot_39

I am a convert to dehumifidiers - so much so I have bought for family in last couple of years - but not saying they are the only way to cope.

But whilst they some consume 250W-300W+ (depending on settings / auto modes) - many if not most will not do so continously in typical use - so they are not really a heater per say - but if ran for several hours - they will obviosly have some impact on room temperatures. 

So don't expect to say it to lift the temperature signficantly in the same say a 1 kW fan heater might do (and even that might struggle in a medium sized room space on a sub zero day - to get much above mid to high teens)

There are as pointed out above - two main types of electric dehumidifiers - compressor and dessicant.

And their are pros and cons.

And the main difference is compressors have a higher temperature requirement.

Compressor models loose their effectiveness at lower temperatures - making them less if not unsuitable for many unhet spaces - like say a cold storage basement or unhet conservatory/caravan - review sites give as examples.

How much does temperature impact extraction - luckily some manufacturers - Meaco for instance table their extraction rates by temp (10,20 and 30C) and 60/80%RH. 

For one of their 20l (and thats per 24 hours) compressor models 

https://www.meaco.com/products/meaco-20l-low-energy-dehumidifier-and-air-purifier

At 60% RH the extraction rate at 10 deg C is 2.52l - and just over a third of the same model at 20C (8.48l).  

At 80% RH 5.86l at 10C - 13.74l at 20C.

That model's table only goes over 20L at 80% 30C - unlikely in UK homes in winter - but possible in summer.

So don't be expecting miracles when you turn yours on for an hour or two - theres a good reason the on board tanks are only 2-3 litres on many models.

And unlike dessicants - the air coming out will be colder than it goes in - as it has been blown across a cold condensing element - think mini air conditioner.  So don't expect it to feel like you've switched on a fan heater right way either. Dessicants however warm the air output - some noticably - in cold spaces - we ran what by domestic standards would be too large in a charity shop basement I used to volunteer at - passing as it does over the "heated to dry" crystals.

12C is lower than most people would heat their home to.  And right to worry about dampness - as many mold articles say heat to 14C to avoid in unventillated - so potentially damp conditions.

I don't run my dehumidifier daily - normally only after laundry in a room space het to about 15C in winter - it helps a lot with dampness. I used to get a lot more condensation on external doors / windows without it - the vents on my windows just not big enough. So much so would have to wipe them dry - especially as wooden framed.

I only normally run it for say 1 or 2 - 2 hour timed sessions at my off peak rate - often pulling over 0.5 pint out of the air - after say a large cottons wash.

But others run them daily and overnight in bedrooms etc. (the human body exhales about 0.4-0.5l per day according to some sites). 

QrizB

Scot_39 said:

And unlike dessicants - the air coming out will be colder than it goes in - as it has been blown across a cold condensing element - think mini air conditioner.  So don't expect it to feel like you've switched on a fan heater right way either.

My experience with compressor dehumidifiers is the opposite to this.

Yes, the dehumidifier cools the air (to get the moisture to condense) on the evaporator coils of the heat pump. But it's then blown over the condenser coils of the heat pump where it picks up all that heat again, plus the latent heat of whatever moisture condensed.

It should come out of the dehumidifier warm(ish).

Using the data from that Meaco link, at 20C and 60% RH it extracts 8.48 litres per day, at an energy use of 219 watts.

In 24 hours it will use 5.25kWh, all of which will end up as heat in the room.

It will also recover (8.48*2.25/3.6) 5.3kWh of heat from the condensed water, which will also end up as heat in the room. That's a 2:1 COP for your heat pump.

GValue

@QrizB Thank you. I didn't know about a COP for these devices :-) It might even reduce energy bills!

QrizB

GValue said:

@QrizB Thank you. I didn't know about a COP for these devices :-) It might even reduce energy bills!

It's only really a saving if you would otherwise have opened a window and let the water vapour blow away. You also get the latent heat back if it condenses on a cold wall (the wall gets slightly warmer).

Personally, I'd rather have a dry house than one with wet walls!

GValue

I've just seen there maybe a link to the moisture in the air and other health conditions
https://www.healthline.com/health/advancing-rheumatoid-arthritis/rheumatoid-arthritis-dehumidifier#climate-and-weather-effects

Scot_39

QrizB said:

Scot_39 said:

And unlike dessicants - the air coming out will be colder than it goes in - as it has been blown across a cold condensing element - think mini air conditioner.  So don't expect it to feel like you've switched on a fan heater right way either.

My experience with compressor dehumidifiers is the opposite to this.

Yes, the dehumidifier cools the air (to get the moisture to condense) on the evaporator coils of the heat pump. But it's then blown over the condenser coils of the heat pump where it picks up all that heat again, plus the latent heat of whatever moisture condensed.

It should come out of the dehumidifier warm(ish).

Using the data from that Meaco link, at 20C and 60% RH it extracts 8.48 litres per day, at an energy use of 219 watts.

In 24 hours it will use 5.25kWh, all of which will end up as heat in the room.

It will also recover (8.48*2.25/3.6) 5.3kWh of heat from the condensed water, which will also end up as heat in the room. That's a 2:1 COP for your heat pump.

Thanks for the info on COP - I must look into that.  

It's a bit easier to just accept the COP on an ASHP/GSHP etc - as the COP energy boost is I believe derived from external air / ground as heat sources.

Its inherently more difficult to think of energy being created in a "closed" system.  But then the room isn't fully closed - it loses or gains heat from other sources - through walls / windows etc.

A quick google came up with links that read more "sales" than science - will look later.

prowla

I think that humidity tends to decrease with temperature.

However the converse doesn't apply; ie. decreasing humidity does not increase temperature.

That said, taking moisture out of the air will decrease condensation when the air hits a cold surface like a window.

fatbelly

I recommend them for older/damper houses. I run 3 on timers to use Economy 7 electricty. Having one in a wet room also means it gets used as a drying room. I have never used a tumble drier and doubt i ever will.

I user the water collected for houseplants to avoid all the stuff in tapwater