Drying Towels in an MVHR fitted bathroom

[Crofter]

24 minutes ago, Onoff said:

 

Going to have a go myself. I've already got the 1.5mm T&E buried under 150mm of Celotex in the ceiling. 

 

It's not an electrician you need, it's a fire engine!

[Onoff]

51 minutes ago, Crofter said:

 

It's not an electrician you need, it's a fire engine!

 

Once I get the Hep2O connections figured it'll be fine.....

[Construction Channel]

I'm sure this has been discussed before but has anyone tried running their UFH through a towel rad style setup?

 

obviously with a bleed valve at the highest point

[Stones]

In our last house we ran a low temp oversized radiator system (33C flow temp at 0C ambient). We had a wet towel rail in the bathroom. Made no difference in terms of speeding up the drying process as it didn't / couldn't throw out anything meaningful heat wise. Not worth the effort IMHO.

[Construction Channel]

4 minutes ago, Stones said:

In our last house we ran a low temp oversized radiator system (33C flow temp at 0C ambient). We had a wet towel rail in the bathroom. Made no difference in terms of speeding up the drying process as it didn't / couldn't throw out anything meaningful heat wise. Not worth the effort IMHO.

very interesting, and pretty much as i suspected BUT did it make your towels nice and warm for when you needed to use them?

[Stones]

No, the flow temp was never high enough.

[Construction Channel]

thanks for that. good to know  

[Construction Channel]

towel weigh in day 2

 

including faye washing her hair and me not wiping myself down,

F: before: 613 after 688

E: before 502 after 579

 

assuming we have a "similar" surface area. (roughly the same height, and certain bumps cancel each other out)

 

looks like i have as much hair on my body as Faye does on her head  

[joe90]

I was planning to have an electric towel radiator in both bathrooms as well as electric UFH and thanks to the above comment wonder if plumbing the radiators into the DHW feed into the adjacent hot water tank from the ASHP would be better.?

[PeterW]

10 minutes ago, joe90 said:

I was planning to have an electric towel radiator in both bathrooms as well as electric UFH and thanks to the above comment wonder if plumbing the radiators into the DHW feed into the adjacent hot water tank from the ASHP would be better.?

 

I considered this but.....

 

My ASHP is going to be doing 2 things - DHW and UFH. One at 48c, the other at 35c to maximize CoP.

 

The downside is that to use the DHW temperature I would need the towel rails on at E7 times rather than when I want them (7-9am & pm) so it would be heating for longer and not at the right times unless I zone the DHW and towel rails somehow. Using PTC elements, a timer and an SSD I am putting the two towel rails and 2 electric UFH mats on a separate power circuit and they will basically be controlled centrally. This will be cheaper I think in the long run and less hassle than piping up multiple runs. 

[joe90]

Yes Peter, similar to you. I had planned E7 for DHW and hoped that towel rails and electric UFH turned off at 6am would still be warm enough by the time we rise!!! Seems a shame not to use the COP of the ASHP and E7 price to reduce heating costs. Then again how much will I be saving if they are on for about an hour each time they are used??? Sometimes we can over complicate these things ?

Edited March 18, 2017 by joe90
Add

[Jeremy Harris]

38 minutes ago, joe90 said:

Yes Peter, similar to you. I had planned E7 for DHW and hoped that towel rails and electric UFH turned off at 6am would still be warm enough by the time we rise!!! Seems a shame not to use the COP of the ASHP and E7 price to reduce heating costs. Then again how much will I be saving if they are on for about an hour each time they are used??? Sometimes we can over complicate these things ?

 

Also worth factoring in the heat pump start up energy consumption when you get down to the sort of low power that a towel rail uses.  A heat pump may well have a longer term COP of over 3, but for the first few minutes when it starts the COP will probably be below 1.  If you then look at the lowest power output that the heat pump can modulate down to (for our unit this is about 1.5 kW) and compare it to the towel rail demand there will be a fairly large mismatch.  So, unless the heat pump is on for some other purpose, it's unlikely to run very efficiently at all for such a small load.

[joe90]

5 minutes ago, JSHarris said:

 

Also worth factoring in the heat pump start up energy consumption when you get down to the sort of low power that a towel rail uses.  A heat pump may well have a longer term COP of over 3, but for the first few minutes when it starts the COP will probably be below 1.  If you then look at the lowest power output that the heat pump can modulate down to (for our unit this is about 1.5 kW) and compare it to the towel rail demand there will be a fairly large mismatch.  So, unless the heat pump is on for some other purpose, it's unlikely to run very efficiently at all for such a small load.

True Jeremy but I was planning to have the towel radiators teed from the hot water tank supply so they were running only when heat was being supplied to the hot water tank, not separately. It still might not be worth the hassle as by say 5 am the DHW tank is up to temp and the radiator will cool off by the time we get up.?

[Jeremy Harris]

Still worth looking at the whole cost, though life, of a wet versus dry system, I think.  An electrically heated towel rail is a fair bit cheaper to install than a plumbed in one.  I reckon a temperature controlled electric towel rail, on for an hour in the morning and an hour in the evening, probably costs around £10 a year to run. 

[Construction Channel]

Has anyone considered putting a "towel warmer" inline on the hot water feed to the shower. Wouldn't help drying anymore than just somewhere to hang a towel. But it would guarantee a nice warm towel when you get out of the shower.  

[Auchlossen]

I am reviving this thread to address another issue. I find that there are some "eco" electric towel rails that are

• DRY, ie do NOT have a glycol filled liquid inside them, and
• use a very low wattage element.

What are the merits of a dry towel rail rather than a wet one?

Here is a good example: Kingston Eco Dry Electric Towel Rail, 600x800mm @ £57

https://www.ebay.co.uk/itm/Kingston-Eco-Dry-Electric-Towel-Warmer-Heated-Towel-Rail-Stainless-Steel-Curved-/322330365216

which runs a 70w heater in stainless steel frame.

What is the opinion of the kirk re this dry strategy rather than a wet solution please?

Has anyone used these Kingston dry rails and can comment on quality?

[ragg987]

I cannot help re the dry part, but the low wattage is not really an advantage imo. A higher power unit with a thermostat that can be dialled low enough will, on average, behave like a low wattage rail but has the advantage of faster heat up times.

 

Our glycol filled electric rail has a 5 step thermostat. I keep it on 24 hours for 2 to 3 months at the lowest setting, I estimate approx 1kWh per day which keeps the bathroom comfortable and towels warm and dry. Rest of the year we turn it on with a countdown timer as required. £10ish per year.

[joe90]

I had not heard of these, I was going to buy oil filled electric radiators for my bathrooms.

[Jeremy Harris]

1 hour ago, joe90 said:

I had not heard of these, I was going to buy oil filled electric radiators for my bathrooms.

 

 

Pretty much any radiator can be turned into an electric one just the same way as any towel rail can, as the fittings are all the same.  Heating elements are available in a side range of lengths and power ratings, so if you like the look of a particular radiator style, then just fit a towel rail element and fill the thing with suitably mixed car antifreeze, the type with corrosion inhibitor.  If you're a cheapskate, then make your own mixture - it's only ethylene glycol water and sodium nitrite (as the corrosion inhibitor), mixed roughly as 30% ethylene glycol, 0.5% sodium nitrite and the rest made up with water to 100%.

 

I tend to buy bulk chemicals that are used in common stuff like this, as it's a heck of a lot cheaper.  My home made windscreen de-icer spray (just isopropyl alcohol, mono ethylene glycol and a tiny amount of salt-free detergent, has been doing well over the past week, when both cars have been well frozen in the mornings.  A 1 litre spray bottle of my home-brew de-icer is around 20% the cost of buying the stuff ready mixed.

[pdf27]

Reading this and got thinking:

• 70g of water seems to be a reasonable estimate for the amount of water on a towel - so it would need to evaporate off 150-300g of water per day without any other drying mechanism at work. Latent heat of evaporation is 2,260 kJ/kg - so between 340 and 680 kJ per day is required. That works out at between 4-8W of additonal heating - it's the being warm rather than the heat energy which makes the difference.
• All else being equal the drying rate will roughly scale with the vapour pressure of water at the towel temperature. Problem is, that doesn't start rising rapidly until the radiator gets fairly warm - at 30°C it's only ~1.5 higher than at 20°C while at 70°C it's 13 times higher.

Looks to me like a heated towel rail will work well in a conventional build where the bathroom needs a significant amount of heating anyway. With smaller heat requirements, unless you want your bathroom a lot warmer than the rest of the house then you're going to struggle to run it warm enough to have any significant drying effect. Given that towel radiators tend to inhibit airflow over the towels compared to a simple towel rail, you may well get dryer towels without it.

[Jeremy Harris]

We have a Victorian-style hoist up, 5 bar airer/drier in the utility room, over the top of the work surface.  That room isn't well heated, it's around 21  deg C usually, just from the UFH, and it's on the North side of the house, pretty much below ground level, with the only light coming from the glazing in the top of the East-facing back door.  There is an MVHR extract terminal immediately above the hoisted airer location.

 

Anything put on that airer and hoisted up dries very quickly, even sopping wet towels.  I think the key is that the MVHR extract is constantly drawing the moist air away, so the RH local to the stuff on the airer is a fair bit lower than it would be otherwise, and this then increases the evaporation rate.

[Bitpipe]

We have a  Lakeland electric clothes horse (integrated element) which we got when living in the caravan and it lived in a greenhouse with the washing machine.  

 

We still use it but almost never use the electric element. We have a heat exchange condensing tumble that only does towels and bedding (super efficiently).

 

Everything else is hung in the utility on the drier and is always dry within 12 hours, quicker on warm days. 

[TerryE]

@pdf27 You are missing one aspect in your heat calc which is that any moisture which condenses out in the MVHR will return this latent heat of evaporation or at least the majority of it back into the house environment.  But now that we are in the house, we find in practice that the towels dry fine without needing a heated rail. We also hive a5-line drier in our services room which has an MVHR extract in it and like JSH says, this will dry a load of washing in about 12 hours.  All of the moisture is recovered in the MVHR condensate or evacuated in the MVHR exhaust.

[Jeremy Harris]

It's an interesting point that the MVHR efficiency figures assume constant RH, I believe, whereas in reality there is a great deal of heat recovery from the condensate on cold days, I'm sure, especially given the high heat capacity of water.

 

I might have a dig around and see what sort of contribution this makes - my guess is that it's pretty significant whenever the MVHR is handling warm, moist air from a shower or bath .

[pdf27]

7 hours ago, TerryE said:

@pdf27 You are missing one aspect in your heat calc which is that any moisture which condenses out in the MVHR will return this latent heat of evaporation or at least the majority of it back into the house environment.  But now that we are in the house, we find in practice that the towels dry fine without needing a heated rail. We also hive a5-line drier in our services room which has an MVHR extract in it and like JSH says, this will dry a load of washing in about 12 hours.  All of the moisture is recovered in the MVHR condensate or evacuated in the MVHR exhaust.

Yeah, I deliberately didn’t consider anything outside the bathroom - I was thinking as to whether it would work at all, not the whole house balance. Essentially the problem is that it doesn’t work without a heat dump, not that it’s inefficient.

I would expect in an MVHR for the exhaust temperature to be pretty constant (set by nominal efficiency at typical humidity). Increasing the humidity in the extract air will increase the condensation rate once the outdoor air is cool enough - pretty much 100% of the additional water being condensed and the energy used to warm the supply air. You can’t be warmer than the supply air, but should be able to get pretty close.