Air con, dehumidifier, extractor fan?

[HappyHippyDad]

I have just done my first workout in my new garden gym. I used my fan heater to get the temperature up to around 12°C which I find about right for a workout. However, the humidity was around 88% which is far too high. There was a lot of condensation on the windows.

My plan was to buy this Rhino AC9000 Portable Air Conditioner & Dehumidifier 2.65kW 240V - https://www.toolstation.com/rhino-ac9000-portable-air-conditioner-dehumidifier/p45462?utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&mkwid=_dc&pcrid=560397125702&pkw=&pmt=&gclid=Cj0KCQiAzfuNBhCGARIsAD1nu-8YZy0q_ygNEEUHec94BGm9xia2MvhO0CJyZwYS04BGFDljb2SCFqgaAunTEALw_wcB&gclsrc=aw.ds

but I thought I'd check to see if this was the best option to keep the humidity under control or if there are better ideas? I fancied the air con as well, to use in mid summer.

The gym is 68mm wood sides . The floor and roof are insulated. It is approx 17Sqm.

Do you have to keep a dehumidifier on all the time, or can I just switch it on when training? From the little I've read, they take 12 hours plus to get to the right humidity, meaning it looks like you just leave them switched on all the time? Pretty expensive!

 

[ImpededLoop]

Ideally you want to ventilate the room, so an extractor fan would probably be best. Otherwise the air will get a bit stale. Make sure that you have a grille that let's in fresh air so that the fan can do its job.

 

[Lucien Nunes]

A certain amount of fresh-air ventilation is necessary, but don't have too much or you will lose heat and gain moisture that then need sorting out.

The amount of time the dehumidifer needs to run depends on how much moisture is getting in, and how efficiently it can extract it which depends on temperature. If the building is fairly moisture-tight, the D/H mainly needs to run when you are in there breathing and sweating. Hopefully it will get far enough ahead of the game during a workout to leave the place dry until next time. Condensation is likely to form, though, as the heated room cools down, unless it is already very dry. Most units contain a humidistat so can be left to cycle on and off as required to pick up moisture that gets in. There is no reason to think it would have to run all the time in a small, reasonably airtight space.

There are two kinds of dehumidifier - this type which is refrigerant (as it's an air-conditioner) and desiccant. Desiccant types work well at low temps and can do useful work while the room is unheated; refrigerant types and convertible D/H - aircon units become much less efficient as the temp approaches freezing. Note that when working as an aircon the exhaust hose has to dump the waste hot air outside and a sufficient fresh-air inlet needs to be allowed, but when used as a D/H the hose needs to be disconnected so that both the hot and cold sides of the unit circulate air within the room.

All the energy a dehumidifer uses appears in the room as heat, so when they are in use in a heated room, the amount of energy you will need to use for the fanheater will be reduced by the same amount. As one of my old mentors (who restored classic cars) used to say; the best garage heater isn't a heater. I actually heat the museum office more or less exclusively with the D/H. We have many units, some of the best are the old refrigerant ones using R12 (Freon), which carry on picking up water at temps where the newer CFC-free ones cop out. But as the temp falls lower only the desiccant ones are any use. We use a combination of separate humidistats, thermostats and timeswitches to run the machines at times when they are most likely to offer the best bang for buck.

 

[HappyHippyDad]

A certain amount of fresh-air ventilation is necessary, but don't have too much or you will lose heat and gain moisture that then need sorting out.

The amount of time the dehumidifer needs to run depends on how much moisture is getting in, and how efficiently it can extract it which depends on temperature. If the building is fairly moisture-tight, the D/H mainly needs to run when you are in there breathing and sweating. Hopefully it will get far enough ahead of the game during a workout to leave the place dry until next time. Condensation is likely to form, though, as the heated room cools down, unless it is already very dry. Most units contain a humidistat so can be left to cycle on and off as required to pick up moisture that gets in. There is no reason to think it would have to run all the time in a small, reasonably airtight space.

There are two kinds of dehumidifier - this type which is refrigerant (as it's an air-conditioner) and desiccant. Desiccant types work well at low temps and can do useful work while the room is unheated; refrigerant types and convertible D/H - aircon units become much less efficient as the temp approaches freezing. Note that when working as an aircon the exhaust hose has to dump the waste hot air outside and a sufficient fresh-air inlet needs to be allowed, but when used as a D/H the hose needs to be disconnected so that both the hot and cold sides of the unit circulate air within the room.

All the energy a dehumidifer uses appears in the room as heat, so when they are in use in a heated room, the amount of energy you will need to use for the fanheater will be reduced by the same amount. As one of my old mentors (who restored classic cars) used to say; the best garage heater isn't a heater. I actually heat the museum office more or less exclusively with the D/H. We have many units, some of the best are the old refrigerant ones using R12 (Freon), which carry on picking up water at temps where the newer CFC-free ones cop out. But as the temp falls lower only the desiccant ones are any use. We use a combination of separate humidistats, thermostats and timeswitches to run the machines at times when they are most likely to offer the best bang for buck.

What would your suggestion be in this case Lucien?

Would (As impededloop says) an extractor fan be the best option, or a desiccant DH?
Perhaps both?
Would it cause problems having the heater on at the same time?

 

[Lucien Nunes]

Yes, they work but the extraction rate drops off rapidly towards 5° or so; check the specs (which don't always say.) There is a design difference between dedicated refrigerant dehumidifiers (which have a small surface area of evaporator that is intended to freeze up and defrost in cycles) and an air-conditioner running as a D/H which has a large evaporator surface and it not intended to freeze. I have much less experience with this as I always use dedicated D/H units.

I would install a small fan for fresh air but probably not rely on extraction to control humidity as it will be unheated for much of the time. If you want aircon for the summer, buy that unit and see whether it's sufficient for your needs as a D/H, it probably will be.

BTW some desiccant D/H units should not be turned on and off by an external stat or timer. When their own stat or switch is used, they enter a cooling cycle before the fan stops to avoid over-cooking the desiccant rotor wih the residual heat in the element.

 

[Jim_e_Jib]

We used to use these desiccant dehumidifiers where I work, running pretty much 24/7 - they proved to be very reliable and effective:

EcoAir DD3 SIMPLE Desiccant Dehumidifier with Nano Silver Filter 10L per day

DD3 Simple Desiccant DehumidifierThis modern and effective desiccant dehumidifier will help you enjoy damp free interiors. Quiet and high efficient Desiccant Dehumidifier ideal for a 3 - 5 bedroom home. It provides moisture removal up to 10 litres per day at 20°C, 60% RH.Powerful Laundry...

ecoair.org

We have a similar sized refrigerant based dehumidifier at home for drying the washing on wet days - I wouldn't be without it!

 

[HappyHippyDad]

Yes, they work but the extraction rate drops off rapidly towards 5° or so; check the specs (which don't always say.) There is a design difference between dedicated refrigerant dehumidifiers (which have a small surface area of evaporator that is intended to freeze up and defrost in cycles) and an air-conditioner running as a D/H which has a large evaporator surface and it not intended to freeze. I have much less experience with this as I always use dedicated D/H units.

I would install a small fan for fresh air but probably not rely on extraction to control humidity as it will be unheated for much of the time. If you want aircon for the summer, buy that unit and see whether it's sufficient for your needs as a D/H, it probably will be.

BTW some desiccant D/H units should not be turned on and off by an external stat or timer. When their own stat or switch is used, they enter a cooling cycle before the fan stops to avoid over-cooking the desiccant rotor wih the residual heat in the element.

I'm wondering if the best option would be as follows..

1. Extractor fan (to aid with air flow, will have window slightly open at same time)
2. Desiccant dehumidifier (to deal with high humidity at very low temperatures, i.e <5°C where I believe a refrigerant DH may not work at all?)
3. Ceiling fan (instead or air con, as we only get short periods of really hot weather)

What do you all reckon?

But..... I guess if I have heated up the room to around 10 - 12°C a refrigerant DH will work!
Is there a portable air con unit with a desiccant dehumidifier?

It's never simple!