Dehumidifiers

Exiled_Tyke

Isn't it the case that a modern tumble drier with a heat pump is using pretty much the same method of drying as a dehumidifier? In which case isn't it likely to be more efficient as it's all concentrated in relatively small tub?  Mine dries a full load of washing for about 1.5 kWh (cupboard dry). How does that compare? 

QrizB

Exiled_Tyke said:

Isn't it the case that a modern tumble drier with a heat pump is using pretty much the same method of drying as a dehumidifier? In which case isn't it likely to be more efficient as it's all concentrated in relatively small tub?  Mine dries a full load of washing for about 1.5 kWh (cupboard dry). How does that compare? 

Most dryers - even "modern" ones - are still vented conventional ones.

But yes, the energy savings vs. a heat pump dryer will be small or zero.

Exiled_Tyke

Appliances Direct are selling 54 Heat Pump models starting at just of £300 compared to 26 vented and 60 condensing. So heat pumps are nowhere as unusual as they were only a couple of years ago.  Hopefully vented and condensing will be banned altogether before too long 

Spies

QrizB said:

There's a small benefit in that you also recover the heat of evaporation from the condensed water. IIRC for a typical 200W dehumidifier this can be around 60 watts, so a space heating COP of 1.3 or so.

Can you elaborate on the science behind this or throw me a link as I'm interested in this side effect. 

QrizB

Spies said:

QrizB said:

There's a small benefit in that you also recover the heat of evaporation from the condensed water. IIRC for a typical 200W dehumidifier this can be around 60 watts, so a space heating COP of 1.3 or so.

Can you elaborate on the science behind this or throw me a link as I'm interested in this side effect. 

Sure, no problems.

When water evaporates it takes heat from the environment. This is why sweating makes you colder, and is how evaporative cooling ("swamp coolers") work. Evaporating 1 litre of water needs about 2.3 MJ of energy - just under two-thirds of a kWh.

If you vent the humid air from the house, this energy goes with it and is lost.

When water condenses it gives that heat out again. And condensing water is what dehumidifiers do.

While dehumidifiers claim huge water removal rates (this one for example claims 20 litres a day) in practice you'll usually get far less, maybe two litres a day. Two litres of condensate represents about 1.3kWh of recovered evaporation energy.

So you'll run your 200 watt dehumidifier for 24 hrs, using 4.8kWh of electricity, and get (4.8+1.3) 6.1kWh of heat back from the system. That's a COP of (6.1/4.8) 1.27.

markin

paul991 said:

Has any one came across a single room through the ceiling mvhr unit

https://www.justfans.co.uk/100-single-room-mvhr-p-3106.html


Here's a video on a larger one from Panasonic
https://www.youtube.com/watch?v=Z45J1hC5IQ0

ispookie666

MVHR if you can have it installed, I looked into it and thought, that's a lot of work! 

We have a dehumidifier for the colder months, dries a full load in 24 hrs. In our old house we used to have a PIV unit(Passive Input Ventilation), which helped a lot with condensation around windows. 

I have literally put a new PIV unit up yesterday - Nuair-Eco. 

Magnitio

ispookie666 said:

MVHR if you can have it installed, I looked into it and thought, that's a lot of work! 

We have a dehumidifier for the colder months, dries a full load in 24 hrs. In our old house we used to have a PIV unit(Passive Input Ventilation), which helped a lot with condensation around windows. 

I have literally put a new PIV unit up yesterday - Nuair-Eco. 

I’ve had a look at these, but didn’t get around to buying. Did you work out the running costs?

legoman62

I replaced my dehumidifier with one of these.
Comes with or without a heater.
Cheap to run and simple to install.
Works a treat.
https://www.i-sells.co.uk/nuaire-drimaster-eco-heat-positive-input-ventilation-unit-with-integral-400w-heater?ref=ViewTitle

ispookie666

@Magnitio I used to have PIV unit in my old home which was installed in 2015 and had a integrated heater, which i had put on a time for a while but turned it off.  AFAIK it was 15w/hr max and the current one ranges from 1.6 - 15.3 w and I'm running it half way.  
PIV units will not help in drying clothes or dealing with wet rooms,  they are very good for houses which suffer from damp, steamed up windows and stale air.