Great video. The solution for new builds and deeper retrofits is to use MVHR. This will deal with the humidity issue but will also bring down other pollutants by supplying fresh air. The heat recovery means you are only loosing a very small amount of heat. (Declaration if interest: my work is designing MVHR systems)
Yes, this is a point I meant to bring up but forgot to mention. This would definitely be my preferred option and I'd love to get a retrofit MVHR system installed at some point.
@@TimAndKatsGreenWalk Be prepared for a £10-15,000 quote for a whole-house MVHR! A good alternative for us was a single-room MVHR, as most of our humidity comes from our shower. £300, and power use is only 5-10W
@@robinbennett5994 yeah, I suspected it'd be a big commitment. I reckon we could get away with it in our bedroom/ensuite only and that would solve 90% of our humidity issues. I'll look into that, thanks (and would you happen to have a recommendation?)!
@@TimAndKatsGreenWalk the most important thing is extractor fans in shower rooms, kitchens etc. They need strong airflow and for showers etc need to run on for 30 minutes. You need 10mm gap at the bottom of the door for air admission. Kitchen extractor needs to be 150mm/6 inch minimum. PIV can be helpful if you have a well ventilated attic space (cold in winter though) but the primary thing should be effective extraction at the source of moisture. Heat recovery is good for air quality and background humidity but not necessarily adequate for bathrooms kitchens etc. That seems to be the best advice I've found. I'm still relying on a dehumidifier as damp is getting under the house but the PIV helps a lot.
Absolutely right. Dry mode cools the air and pumps the heat out of your house. Not ideal in winter. I have a portable dehumidifier (meaco arete1 12l) set to 60% rh. It runs at 150W when on and uses between 1 to 2.5kWh per day. It switches itself off when it gets down to the right humidity so doesn't use much energy unless it is mild and wet outside. The dehumidifier dumps it's heat into the room so even better. Some people set the humidity level too low which just wastes energy. Because houses are leaky you will never lower the dew point of the house below that of the outside unless you have a really powerful machine. This is ok in winter as the inside is significantly warmer than the outside so rel humidity is lower with same dew point. Typically I empty the dehumidifier collection tank once per day (about 2litres). You could plumb it into a permanent drain but then it's not so portable. My small dehumdifier keeps a 6 room house condensation free all winter. No more mouldy windows frames and misted windows panes.
Yeah, ours also cut out at a given humidity depending on the settings you use. I usually aim for between 50 and 60%, as there's not much point going lower than that, as you say.
Nice info Tim. "Dry Mode" is a feature found on most Japanese / far east manufactured HVAC equipment to combat the high humidity conditions they experience during certain times of the year e.g. monsoon season when it is both warm & very humid. It's a way of reducing the room humidity without reducing the room temperature too much - but it does. It's not a control feature we use very much in Europe / UK for residential applications. An additional point to bare in mind. Selecting Dry mode (low fan cooling) on some HVAC indoor units means that Heat mode on others indoor units cannot operate at the same time, when they are connected to the same outdoor unit. One mode or or the other but not at the same time. It's one of the restrictions of a Multi Split HP AC system. That said you have two outdoor units / systems so it would be possible to have Dry mode operating on one system indoor units & heating on the other system indoor units if needed. I agree, compressor dehum units are more effective than the dessicant type but they consume more energy & are noisier. However, as you pointed out the warm exhaust air from the dehum units is a positive heat gain to the room so it's not wasted & a benefit during the heating season. Basically the compressor dehumidifier unit operate the same way as your split AC system does in heating mode but with both halves of the system (evaporator & condenser) in the same unit & not split apart.
Yes, I didn't mention the point about not being able to mix modes for a multi-split system but you're right. I've found that our compressor dehumidifier runs at a lower power than the desiccant one though, and extracts more water per kWh used, for our particular situation. That will differ depending on the temperature and humidity.
I think that's a good explanation Tim. So far this year I've only ever used the dry mode for cooling the house as I find it's usually not too hot, but too humid. The difference between outside humid 22c and inside dry 22c is mind boggling, you wouldn't know that inside and outside are the same temperature!
On my a/c units (I have one Daikin and one MHI), all the dry mode seems to do is run it on cooling with the lowest fan speed. In summer, unless it's really really hot I tend to have the a/c on a low fan setting anyway.
Very informative as usual, thanks for sharing Tim. I lived in Malta for several years and quickly figured out their houses are built to exclude heat better and not so good for humidity. I think dehumidifiers are better for health and your pocket - both in winter and summer. Excess humidity is not only bad for our lungs, it makes rooms feel musty, it makes us feel a lot colder/hotter so we need additional heating/cooling. When humidity levels lowered, you realise you didn't need heating/cooling, it's around 20C inside
Thanks. Particularly appreciated the point about latent heat being released on condensation. Transported back to my school days! Living in a fairly leaky older house that very rarely has any issues with condensation the whole thing about humidty and dehumidifiers has rather passed us by. But I'm now feeling that we ought to be paying it a bit more attention, particularly if they can be run overnight on cheap electricity whilst also helping to warm the house.
The irony is that a leaky house is probably less susceptible to high humidity because the air changes more often! That's probably why you don't have condensation issues. I'm glad you appreciated the latent heat mention. It's always good to get a bit of science into these videos somehow!
Great video. It also takes less energy to heat dry air, it's the opposite to a spray water cooler, water takes more energy to heat, I think you covered the SHC of water in a previous video actually.
We have just completed a house renovation including a new extension, whole house MVHR and an air-air unit in the main living area of an open plan layout. The MVHR has a humidity sensor which boosts the flow when humidity increases; it can also be temporarily boosted by switches in the kitchen and bathrooms. Compared to last winter the house is warmer, we have zero condensation and we have significantly reduced energy consumption and bills . Installing the MVHR was not actually that difficult but did need some boxing installed down the corners of a couple of upstairs rooms to carry ducts to the downstairs. This will depend on where you site the MVHR unit and also things such as your floor joists. No problem at all if you live in a bungalow though. Dry mode on AC typically works by cooling the temperature by around 2 deg C from the ambient temperature. When we lived in Cyprus the relative humidity would increase when the air temperature dropped in the evening (the amount of moisture that air can hold is relative to the temperature) and the dry mode would work well. Not much good in the UK winter when we are trying to keep warm. As you describe the compressor dehumidifiers are the ticket here, as they cool the air causing the moisture to condense then heat it up again after - unless you have MVHR of course.
MVHR is on my list of future home improvements, for sure. I'm wondering if in the meantime I can get away with replacing the extractor fan in our ensuite with a single room MVHR unit, or if I should hold off and just go with an all-house solution down the line. Out of interest, would you mid telling me how much your whole house MVHR solution cost you? I think I might be able to get away with it just in the upstairs.
@@TimAndKatsGreenWalk I was able to buy a vent-axia sentinel kinetic unit that had been fitted then removed because it was incorrectly specified. This cost me £600. Try looking at kawavent though as they seem to offer some cheaper units. I bought the ducting etc from BPC - they offer a free design service. Check their quote carefully though because they supplied me far more duct pipe than I needed. Air supply vents are generally fitted in the bedrooms and other living areas, with extracts in the bathrooms and kitchen. The air then flows from bedrooms towards the more humid areas before being extracted. The semi-rigid ducting is easy to work with. Just make sure it is well covered insulation in the loft. I fitted the mvhr unit in the airing cupboard - it is best to mount it in a warm area with access so the filters can cleaned. The other job was to connect the unit to the outside of the house - I hired a core drill for the day and fortunately was able to use the builders' scaffold to drill the 2 holes through the gable wall. For the system to run most efficiently, the house should be as draft proof as possible - we blocked the previous air bricks and had the new double glazing installed without trickle vents. I'm not sure how that would work if you are only planning on doing upstairs.
Thanks, that's some really useful information. I'm unlikely to do anything about this within the next year or so but it's good to know what the options are for planning ahead.
Perfectly explained, and very useful. Thanks very much. Have you ever considered installing a mechanical ventilation with heat recovery (MVHR) system? I've lived in a flat with MVHR and I must say it is comfortable. Plus it feeds oxygen into the room and prevents build up of CO2. Would be a few grand though and quite an invasive installation!
Thank you. And yes, MVHR is exactly the system I've been considering and would very much like to get installed at some point. It's on my radar for a future upgrade but might be a while before we can do it.
We’ve been investigating this because when it’s wet outside we can get 70+ humidity, but to get a decent system is pretty disruptive and not cheap, it’s on the list of things I’d like to get but can’t afford right now
I have the same Toshiba system as you Tim - i find heat mode does a great job of drying out the rooms to the point of no longer having condensation on my windows in the morning. Haven't tried dry mode but also won't bother after seeing your video. The heat pump system works very well.
Sadly that doesn't seem to work in our house. The humidity stays the same when running in heating mode. It's our stupid metal framed windows that are the real problem. Even modern ones like ours are still prone to condensation when it gets really cold outside, hence our use of the dehumidifiers. I doubt we'd have a problem if the frames were a more sensible material!
We are renovating an old cottage and have come across absolute vs relative humidity. I believe only VapourFlow fans are able to do this and have patented the tech. Worth a read, worth considering if ever replacing extractors etc in future.
@@TimAndKatsGreenWalk VIP treatment! I'll have to watch it again and see if I can spot the red carpet being rolled out in the background 😁 What can I request next?🤔😉
@@UpsideDownFork this video was partly inspired by your question on my latest stats video, and the fact that a few others have asked something similar before too. So yeah, it was basically for you!
This is facinating. Like you I tried using dry mode to dry clothes but found the cold air offputting. I'd be very interested in learning about how effective a dehumidifier is at helping to dry clothing (perhaps a test could be carried out drying with and without the dehumidifier). I'm interested because the alternative is one of those heated clothes dryers which seemed wasteful.
The dehumidifier that we use in the room where we dry the laundry is very effective, for sure. I've not done a scientific comparison but when we use the dehumidifier overnight the clothes are noticeably drier in the morning.
I tried our portable AC in dehumidifier mode, but like you I found it was cold air coming out, plus the power use for us was 800w. Compare this to the standalone dehumidifier units, which uses 180w on high. So the A/C has gone in storage. Bonus is that the dehumidifier unit seems to add a little heat back into the room too.
Yes, indeed, that is something I'd like to do and am investigating. I'd love a full house MVHR system but that might be too much for the near term, although there are some single room solutions that could help in our bedroom in the first instance.
@@TimAndKatsGreenWalk Yeah, at some point the fan in my bathroom needs replacing, I have been looking at a heat recovery option for that. But they extend out further and there is a walkway right next to the bathroom. Would like to work out a way to reduce the amount it sticks out from the wall!
@@TimAndKatsGreenWalk ...or cools down in the summer. The absolute humidity of the fresh air from the intake will be the same as of the air outside. An HRV can only transfer heat between the crossing airstreams. The ERV units have for ex. a special membrane like stuff in the core which allows the humidity "exchange" while still separating the fresh air from the extracted air.
Hi Tim I have just bought two desiccant meaco junior DD8L dehumidifiers primarily because they produce more heat. So far we haven’t used are air con system to heat the house yet as it’s so warm outside but have used the dehumidifiers to reduce the humidity like you for a few hours a day. As a family of four there is a lot of laundry and I put them both on at night mainly during the off peak period to dry it and I am quite surprised how dry it gets them with the added benefit of having a warm house when we get up. I am hoping not to use the tumble dryer this winter.😀
Thanks for the video. We have a very similar system to yours installed a couple of months ago and, using dehumidifiers regularly, I wondered how the dry mode compaired...now I know
I also discovered this recently too - my mini-split has a fixed set temp of 3C below the ambient to "dehumidify" so just blasts out cold air - may as well open the windows 😂 - the small Aldi compressor dehumidifier I have uses 200W and actually warms a decent amount which seems to make more sense...I run it when there is a sufficient amount of PV during the day...
@@TimAndKatsGreenWalk yep it's always nice to have a full battery, fully heated tank of hot water and getting the humidity down for 6 hours or so - there have been very few "full sun" days the last couple of months so it's a pleasant surprise 😀
I use a desiccant type as a source of heating. My living area (at the time of writing) goes up from 12C to 16C. My house seems to be humid all the time (70%) so this setup works quite well. I know this sounds counter intuitive. Wouldn't it be better to have a cold house especially if you are not in it. The reason being, cold air hold less moisture.
The colder your house the more likely there will be cold surfaces where moisture will condense, so more likely to develop mould. The relative humidity will actually go up the colder it gets because, as you say, warm air can hold more moisture, so for the same absolute humidity a cold house will have a higher relative humidity.
Compressor dehumidifiers are more efficient at warm temperatures and dessicant at low temps (just above freezing). Reason being compressor dehumidifiers chill the air to extract the moisture (they reheat it as well). Dessicant dehumidifiers use heat to extract the moisture and room temp air to condense it. Therefore the greater the temperature difference in both cases the more effective they are. Dessicant versions are more versatile, lighter and quieter but maybe more expensive to run in heated spaces. They will outperform compressor dehumidifiers at low temps.
Yup, I've found our compressor one extracts more water per kWh input, so use that in preference. The desiccant one is much quieter though, so is better for running overnight in rooms near to our bedroom.
Yes, I have both compressor and desiccant dehumidifiers, with one in the cellar. These are normally run on our off peak hour tariff (Econ 7). A lot of the time I just run the compressor dehumidifier, but when I want to dry clothes quickly I have both on - the desiccant based unit is also much easier to move round. As you say, when it is really cold, the compressor based dehumidifier spends an amount of time in defrost mode - mine does some sort of reverse cycle where the coils that are normally cold are heated slightly to melt the frost... and in these conditions the desiccant dehumidifier actually extracts more water.
The big issue with using AC in dry mode is that much of the water stays on the heat exchanger and when you turn it back in heating mode it immediately evaporates and increases the humidity. I find it useful during the time period when the outside temps are warm enough that you don't need to turn on heating.
I think it’s strange how my desiccant dehumidifier will get 3 ltrs of water out of the air in less than 6hours. It’s always odd pouring all that water out in the morning. Bonus is it keeps the house warm.
My humidity problems are in the garage. Tools (and motorbike exhausts) rust and cardboard boxes get soggy in the winter. Any tips for a humidifier that works well at just above freezing?
Most of the issues are in our bedroom caused by Kat and I breathing overnight. The dehumidifier in the room where we dry the laundry is very effective at handling the humidity there, so that's working pretty well.
Interesting. I've read (in books from the UK) that (centrally) heated houses have the opposite problem: Too dry in the winter, making the rooms feel colder. (Due to warmed air being able to hold more moisture than the colder outside air.) My problem is that humidity can drop to 27% during cold periods. Maybe Holland has colder, drier winters than the UK?
I think it depends a lot on the fabric of the house too. It does get particularly wet in the UK in Winter so I suspect that's the main culprit for our situation. When it's very cold and dry here (quite rare) I definitely see the indoor humidity drop too, although it rarely gets lower than about 40%.
@@FoxInClogs I don't believe so. The AC units circulate the air pretty nicely and we don't have any damp/mould issues anywhere. The only condensation problems we have are on our metal framed windows (I hate them), usually only really our bedroom windows. If I could change those frames that'd help a lot but it'd be extremely costly. I'm considering other ways to reduce that particular problem (e.g. linings on the inside of the window frames) but that is ongoing at present.
That's easy: Dehumidifier, our 3x3.5 m server room had 2 x 2200bts aircons, the humidity was often over 75%, it was not until we got a dehumidifier that it came down to 45-60%
Sounds like oversized AC (I'm guessing you meant 22,000BTU not 2,200BTU). For the size of the room, one likely would have sufficed (and might have even been oversized on its own). For AC's to dehumidify, they need to be actively cooling - i.e. compressor running outside. If the compressor is turning on and off because the room is already cold enough then they won't dehumidify effectively.
Generally I'd run it in cooling mode in the Summer, as required, but mostly to reduce the temperature rather than the humidity. And even then we use it pretty rarely in cooling mode, only usually when we get a bit of a heat wave. We tend not to have a humidity problem in the Summer, thankfully, it's usually from about Oct to April that we need to run the dehumidifiers at all. Dry mode is essentially just a low power version of cooling mode, so I'm not really sure it should count as a whole separate mode, to be honest!
A heat pump that has a dry vs cool mode doesn't differ in functionality if you need to cool the house anyway. The only difference between cool mode and dry mode is that in cool mode the unit will either turn off or just run the fan once the inside temperature is low enough and in dry mode if it gets too cold inside it will run the cycle in reverse a bit to add the heat that was previously removed back in to the house. In both cool and dry mode when it is removing heat the inside unit will get condensation on it which gets removed from the house by either pump or gravity.
Hi Tim , great video, I am thinking of getting a dehumidifier. One thing, you say you use on your cheap rate during the night. Is this a special feature on the unit or do you just push the on button and use a timer, Jamie
Ah, good question. I use smart plugs with a timer that turns them on at the time I specify (I have the GivEnergy smart plugs which show up in my GivEnergy app). The dehumidifiers themselves don't have a timer function, sadly (although some might, I've not checked).
I have both types of de humidifier. With the desiccant type, smart plug is ok to turn it on but not off. The instructions warn you to not turn it off at the plug because it needs to cool down using its fan for a couple of minutes. It is also much more efficient in colder temperatures. With the compressor type, the smart plug is a great way of controlling it. It is much more efficient above 15C or so. Forget it below this temp.
You can't do anything while the outside unit is doing its defrost cycle unfortunately, because it's busy doing the defrost cycle and shuts down all the indoor units. And that only takes about 5 mins, so wouldn't be particularly effective anyway.
There is another type of dehumidifier which uses semi-conductor technology called a Peltier dehumidifier. So again no refrigerant, allowing them to be smaller. My wife bought one from Aldi this week and according to the manual uses the technology. However, I have to say I'm not impressed - it's very slow to collect water and apparently the most inefficient type of dehumidifier. It just doesn't compare to my Ariadry (same model as yours) which I got very cheaply secondhand a few years back.
Interesting, I'd not heard of that type of dehumidifier before. Sounds like it's not worth bothering with if it's so inefficient. Interesting nonetheless.
Peltier's are notoriously inefficient and get less so as the temperature difference between the plates increases. I have a 12V insulated cooler/heater that uses one that I use for food delivery. It uses about 4 times the power that a compressor based cooler would use... But there are no reversible compressor based portable coolers that can get hot inside. So, like most tools they have some uses, but the trade-offs are so much in this case other options are almost always better. One advantage is that it could be completely silent. Compressor based dehumidifiers are notoriously noisy, especially cheap ones.
Did you consider PIV ? i.e. filtered tepid air in which finds it's own way out at minimal power consumption. I just fitted one in my loft to see how it goes - immediate changes are a fresher/brighter? (not sure how to describe it) feel to the air without being particularly colder. It may even help stop stratification of Aircon air in the stairwell. My house is not suitable for a full blown MHVR, it's the age where finding holes/sealing it in any reasonable way just isn't possible without some sort of major rebuild!
Great video.
The solution for new builds and deeper retrofits is to use MVHR. This will deal with the humidity issue but will also bring down other pollutants by supplying fresh air. The heat recovery means you are only loosing a very small amount of heat.
(Declaration if interest: my work is designing MVHR systems)
Yes, this is a point I meant to bring up but forgot to mention. This would definitely be my preferred option and I'd love to get a retrofit MVHR system installed at some point.
@@TimAndKatsGreenWalk Be prepared for a £10-15,000 quote for a whole-house MVHR! A good alternative for us was a single-room MVHR, as most of our humidity comes from our shower. £300, and power use is only 5-10W
@@robinbennett5994 yeah, I suspected it'd be a big commitment. I reckon we could get away with it in our bedroom/ensuite only and that would solve 90% of our humidity issues. I'll look into that, thanks (and would you happen to have a recommendation?)!
Within a room, how important is vent placement?
@@TimAndKatsGreenWalk the most important thing is extractor fans in shower rooms, kitchens etc. They need strong airflow and for showers etc need to run on for 30 minutes. You need 10mm gap at the bottom of the door for air admission. Kitchen extractor needs to be 150mm/6 inch minimum. PIV can be helpful if you have a well ventilated attic space (cold in winter though) but the primary thing should be effective extraction at the source of moisture. Heat recovery is good for air quality and background humidity but not necessarily adequate for bathrooms kitchens etc. That seems to be the best advice I've found. I'm still relying on a dehumidifier as damp is getting under the house but the PIV helps a lot.
Absolutely right. Dry mode cools the air and pumps the heat out of your house. Not ideal in winter.
I have a portable dehumidifier (meaco arete1 12l) set to 60% rh. It runs at 150W when on and uses between 1 to 2.5kWh per day. It switches itself off when it gets down to the right humidity so doesn't use much energy unless it is mild and wet outside. The dehumidifier dumps it's heat into the room so even better. Some people set the humidity level too low which just wastes energy. Because houses are leaky you will never lower the dew point of the house below that of the outside unless you have a really powerful machine. This is ok in winter as the inside is significantly warmer than the outside so rel humidity is lower with same dew point.
Typically I empty the dehumidifier collection tank once per day (about 2litres). You could plumb it into a permanent drain but then it's not so portable. My small dehumdifier keeps a 6 room house condensation free all winter. No more mouldy windows frames and misted windows panes.
Yeah, ours also cut out at a given humidity depending on the settings you use. I usually aim for between 50 and 60%, as there's not much point going lower than that, as you say.
Nice info Tim.
"Dry Mode" is a feature found on most Japanese / far east manufactured HVAC equipment to combat the high humidity conditions they experience during certain times of the year e.g. monsoon season when it is both warm & very humid. It's a way of reducing the room humidity without reducing the room temperature too much - but it does. It's not a control feature we use very much in Europe / UK for residential applications.
An additional point to bare in mind. Selecting Dry mode (low fan cooling) on some HVAC indoor units means that Heat mode on others indoor units cannot operate at the same time, when they are connected to the same outdoor unit. One mode or or the other but not at the same time. It's one of the restrictions of a Multi Split HP AC system. That said you have two outdoor units / systems so it would be possible to have Dry mode operating on one system indoor units & heating on the other system indoor units if needed.
I agree, compressor dehum units are more effective than the dessicant type but they consume more energy & are noisier. However, as you pointed out the warm exhaust air from the dehum units is a positive heat gain to the room so it's not wasted & a benefit during the heating season. Basically the compressor dehumidifier unit operate the same way as your split AC system does in heating mode but with both halves of the system (evaporator & condenser) in the same unit & not split apart.
Yes, I didn't mention the point about not being able to mix modes for a multi-split system but you're right. I've found that our compressor dehumidifier runs at a lower power than the desiccant one though, and extracts more water per kWh used, for our particular situation. That will differ depending on the temperature and humidity.
I think that's a good explanation Tim. So far this year I've only ever used the dry mode for cooling the house as I find it's usually not too hot, but too humid. The difference between outside humid 22c and inside dry 22c is mind boggling, you wouldn't know that inside and outside are the same temperature!
Yes, it's surprising how much of a difference the humidity level can have on comfort.
On my a/c units (I have one Daikin and one MHI), all the dry mode seems to do is run it on cooling with the lowest fan speed. In summer, unless it's really really hot I tend to have the a/c on a low fan setting anyway.
@@markingle8487 yup, that's exactly what dry mode is. I think it's a bit much to call it an entirely different mode, tbh.
Very informative as usual, thanks for sharing Tim. I lived in Malta for several years and quickly figured out their houses are built to exclude heat better and not so good for humidity. I think dehumidifiers are better for health and your pocket - both in winter and summer. Excess humidity is not only bad for our lungs, it makes rooms feel musty, it makes us feel a lot colder/hotter so we need additional heating/cooling. When humidity levels lowered, you realise you didn't need heating/cooling, it's around 20C inside
Yup, it definitely makes a difference.
Thanks. Particularly appreciated the point about latent heat being released on condensation. Transported back to my school days!
Living in a fairly leaky older house that very rarely has any issues with condensation the whole thing about humidty and dehumidifiers has rather passed us by. But I'm now feeling that we ought to be paying it a bit more attention, particularly if they can be run overnight on cheap electricity whilst also helping to warm the house.
The irony is that a leaky house is probably less susceptible to high humidity because the air changes more often! That's probably why you don't have condensation issues. I'm glad you appreciated the latent heat mention. It's always good to get a bit of science into these videos somehow!
Great video. It also takes less energy to heat dry air, it's the opposite to a spray water cooler, water takes more energy to heat, I think you covered the SHC of water in a previous video actually.
Yes, that is also true. It's a fairly minor effect but it all makes a difference.
We have just completed a house renovation including a new extension, whole house MVHR and an air-air unit in the main living area of an open plan layout. The MVHR has a humidity sensor which boosts the flow when humidity increases; it can also be temporarily boosted by switches in the kitchen and bathrooms. Compared to last winter the house is warmer, we have zero condensation and we have significantly reduced energy consumption and bills .
Installing the MVHR was not actually that difficult but did need some boxing installed down the corners of a couple of upstairs rooms to carry ducts to the downstairs. This will depend on where you site the MVHR unit and also things such as your floor joists. No problem at all if you live in a bungalow though.
Dry mode on AC typically works by cooling the temperature by around 2 deg C from the ambient temperature. When we lived in Cyprus the relative humidity would increase when the air temperature dropped in the evening (the amount of moisture that air can hold is relative to the temperature) and the dry mode would work well. Not much good in the UK winter when we are trying to keep warm. As you describe the compressor dehumidifiers are the ticket here, as they cool the air causing the moisture to condense then heat it up again after - unless you have MVHR of course.
MVHR is on my list of future home improvements, for sure. I'm wondering if in the meantime I can get away with replacing the extractor fan in our ensuite with a single room MVHR unit, or if I should hold off and just go with an all-house solution down the line. Out of interest, would you mid telling me how much your whole house MVHR solution cost you? I think I might be able to get away with it just in the upstairs.
@@TimAndKatsGreenWalk I was able to buy a vent-axia sentinel kinetic unit that had been fitted then removed because it was incorrectly specified. This cost me £600. Try looking at kawavent though as they seem to offer some cheaper units. I bought the ducting etc from BPC - they offer a free design service. Check their quote carefully though because they supplied me far more duct pipe than I needed.
Air supply vents are generally fitted in the bedrooms and other living areas, with extracts in the bathrooms and kitchen. The air then flows from bedrooms towards the more humid areas before being extracted.
The semi-rigid ducting is easy to work with. Just make sure it is well covered insulation in the loft.
I fitted the mvhr unit in the airing cupboard - it is best to mount it in a warm area with access so the filters can cleaned.
The other job was to connect the unit to the outside of the house - I hired a core drill for the day and fortunately was able to use the builders' scaffold to drill the 2 holes through the gable wall.
For the system to run most efficiently, the house should be as draft proof as possible - we blocked the previous air bricks and had the new double glazing installed without trickle vents. I'm not sure how that would work if you are only planning on doing upstairs.
Thanks, that's some really useful information. I'm unlikely to do anything about this within the next year or so but it's good to know what the options are for planning ahead.
Perfectly explained, and very useful. Thanks very much.
Have you ever considered installing a mechanical ventilation with heat recovery (MVHR) system? I've lived in a flat with MVHR and I must say it is comfortable. Plus it feeds oxygen into the room and prevents build up of CO2.
Would be a few grand though and quite an invasive installation!
Thank you. And yes, MVHR is exactly the system I've been considering and would very much like to get installed at some point. It's on my radar for a future upgrade but might be a while before we can do it.
We’ve been investigating this because when it’s wet outside we can get 70+ humidity, but to get a decent system is pretty disruptive and not cheap, it’s on the list of things I’d like to get but can’t afford right now
I have the same Toshiba system as you Tim - i find heat mode does a great job of drying out the rooms to the point of no longer having condensation on my windows in the morning. Haven't tried dry mode but also won't bother after seeing your video. The heat pump system works very well.
Sadly that doesn't seem to work in our house. The humidity stays the same when running in heating mode. It's our stupid metal framed windows that are the real problem. Even modern ones like ours are still prone to condensation when it gets really cold outside, hence our use of the dehumidifiers. I doubt we'd have a problem if the frames were a more sensible material!
@@TimAndKatsGreenWalk
Isn't that a ventilation problem?
What about heat recovery ventilation?
@@Paul-yh8km potentially. MVHR is something I am also investigating. I'm certain that would help.
We are renovating an old cottage and have come across absolute vs relative humidity. I believe only VapourFlow fans are able to do this and have patented the tech. Worth a read, worth considering if ever replacing extractors etc in future.
Thanks, I'll take a look.
Thanks for taking the time to make this video. Really helpful! 😊
This one was just for you 😉
@@TimAndKatsGreenWalk VIP treatment!
I'll have to watch it again and see if I can spot the red carpet being rolled out in the background 😁
What can I request next?🤔😉
@@UpsideDownFork haha! It seems like you're not lacking ideas for your own videos so any you don't want to do just sling 'em my way!
@@UpsideDownFork this video was partly inspired by your question on my latest stats video, and the fact that a few others have asked something similar before too. So yeah, it was basically for you!
Such a great video, Tim - I learned a lot! 😃👍
Thanks Gary. I'd say the net amount of learning is very much from your channel to mine though ;)
This is facinating. Like you I tried using dry mode to dry clothes but found the cold air offputting. I'd be very interested in learning about how effective a dehumidifier is at helping to dry clothing (perhaps a test could be carried out drying with and without the dehumidifier). I'm interested because the alternative is one of those heated clothes dryers which seemed wasteful.
The dehumidifier that we use in the room where we dry the laundry is very effective, for sure. I've not done a scientific comparison but when we use the dehumidifier overnight the clothes are noticeably drier in the morning.
I tried our portable AC in dehumidifier mode, but like you I found it was cold air coming out, plus the power use for us was 800w. Compare this to the standalone dehumidifier units, which uses 180w on high. So the A/C has gone in storage.
Bonus is that the dehumidifier unit seems to add a little heat back into the room too.
Yup, dehumidifiers are definitely a better solution, I reckon.
Wouldn't it be better to have heat recovery ventilation installed?
Wouldn't that remove most of the moisture and also replace the air.
Yes, indeed, that is something I'd like to do and am investigating. I'd love a full house MVHR system but that might be too much for the near term, although there are some single room solutions that could help in our bedroom in the first instance.
@@TimAndKatsGreenWalk
Yeah, at some point the fan in my bathroom needs replacing, I have been looking at a heat recovery option for that.
But they extend out further and there is a walkway right next to the bathroom.
Would like to work out a way to reduce the amount it sticks out from the wall!
The heat recovery units are doing nothing with the moisture, you need an energy recovery unit to control the humidity to some extend.
@@raysstuffz you're pulling in air from outside which results in a lower relative humidity when it warms up on the way in.
@@TimAndKatsGreenWalk ...or cools down in the summer. The absolute humidity of the fresh air from the intake will be the same as of the air outside. An HRV can only transfer heat between the crossing airstreams. The ERV units have for ex. a special membrane like stuff in the core which allows the humidity "exchange" while still separating the fresh air from the extracted air.
Hi Tim I have just bought two desiccant meaco junior DD8L dehumidifiers primarily because they produce more heat. So far we haven’t used are air con system to heat the house yet as it’s so warm outside but have used the dehumidifiers to reduce the humidity like you for a few hours a day. As a family of four there is a lot of laundry and I put them both on at night mainly during the off peak period to dry it and I am quite surprised how dry it gets them with the added benefit of having a warm house when we get up. I am hoping not to use the tumble dryer this winter.😀
They are very effective for drying clothes, I agree! And as you say, it's a nice boost of heat too.
Thanks for the video. We have a very similar system to yours installed a couple of months ago and, using dehumidifiers regularly, I wondered how the dry mode compaired...now I know
Glad I could help! It's always worth running your own experiments, but I suspect you'd find a similar result to us.
I suspect so too being as the air to air chucks heat out through the external unit whilst a dehumidifier keeps it all indoors.
@@tonygarlick7775 yes, exactly.
Excellent summary Tim.
Thanks.
I also discovered this recently too - my mini-split has a fixed set temp of 3C below the ambient to "dehumidify" so just blasts out cold air - may as well open the windows 😂 - the small Aldi compressor dehumidifier I have uses 200W and actually warms a decent amount which seems to make more sense...I run it when there is a sufficient amount of PV during the day...
I do the same. In fact I ran it today while we had a bit of extra sun!
@@TimAndKatsGreenWalk yep it's always nice to have a full battery, fully heated tank of hot water and getting the humidity down for 6 hours or so - there have been very few "full sun" days the last couple of months so it's a pleasant surprise 😀
I use a desiccant type as a source of heating. My living area (at the time of writing) goes up from 12C to 16C. My house seems to be humid all the time (70%) so this setup works quite well.
I know this sounds counter intuitive. Wouldn't it be better to have a cold house especially if you are not in it. The reason being, cold air hold less moisture.
The colder your house the more likely there will be cold surfaces where moisture will condense, so more likely to develop mould. The relative humidity will actually go up the colder it gets because, as you say, warm air can hold more moisture, so for the same absolute humidity a cold house will have a higher relative humidity.
Thanks for the quick answer really helpful thanks, Jamie
No problem.
Compressor dehumidifiers are more efficient at warm temperatures and dessicant at low temps (just above freezing). Reason being compressor dehumidifiers chill the air to extract the moisture (they reheat it as well). Dessicant dehumidifiers use heat to extract the moisture and room temp air to condense it. Therefore the greater the temperature difference in both cases the more effective they are. Dessicant versions are more versatile, lighter and quieter but maybe more expensive to run in heated spaces. They will outperform compressor dehumidifiers at low temps.
Yup, I've found our compressor one extracts more water per kWh input, so use that in preference. The desiccant one is much quieter though, so is better for running overnight in rooms near to our bedroom.
@@TimAndKatsGreenWalk I think Nigel found the tipping point to be about 16°C where the compressor model starts losing on litres/kWh.
@@matthewwakeham2206 that feel about right, yeah.
Yes, I have both compressor and desiccant dehumidifiers, with one in the cellar. These are normally run on our off peak hour tariff (Econ 7). A lot of the time I just run the compressor dehumidifier, but when I want to dry clothes quickly I have both on - the desiccant based unit is also much easier to move round. As you say, when it is really cold, the compressor based dehumidifier spends an amount of time in defrost mode - mine does some sort of reverse cycle where the coils that are normally cold are heated slightly to melt the frost... and in these conditions the desiccant dehumidifier actually extracts more water.
The big issue with using AC in dry mode is that much of the water stays on the heat exchanger and when you turn it back in heating mode it immediately evaporates and increases the humidity. I find it useful during the time period when the outside temps are warm enough that you don't need to turn on heating.
That's a good point.
I think it’s strange how my desiccant dehumidifier will get 3 ltrs of water out of the air in less than 6hours. It’s always odd pouring all that water out in the morning. Bonus is it keeps the house warm.
Yeah, it's impressive how effective they are! I use some of the water on our houseplants when they need it.
My humidity problems are in the garage. Tools (and motorbike exhausts) rust and cardboard boxes get soggy in the winter.
Any tips for a humidifier that works well at just above freezing?
I believe the desiccant ones are supposed to work better in low temperature situations, so that would be the type to look for.
in indonesia often we have high humidity >70% and high temp 35 degrees celcius so using dry mode is the best
Yeah, that's it's intended purpose, really, not damp cold UK!
Could it be that the indoor laundry drying is causing the problem? A heat pump clothes dryer would efficiently eliminate that source of humidity.
Most of the issues are in our bedroom caused by Kat and I breathing overnight. The dehumidifier in the room where we dry the laundry is very effective at handling the humidity there, so that's working pretty well.
Interesting. I've read (in books from the UK) that (centrally) heated houses have the opposite problem: Too dry in the winter, making the rooms feel colder. (Due to warmed air being able to hold more moisture than the colder outside air.)
My problem is that humidity can drop to 27% during cold periods. Maybe Holland has colder, drier winters than the UK?
I think it depends a lot on the fabric of the house too. It does get particularly wet in the UK in Winter so I suspect that's the main culprit for our situation. When it's very cold and dry here (quite rare) I definitely see the indoor humidity drop too, although it rarely gets lower than about 40%.
Living room humidity is 54% at the moment, BTW with 13°C / 86% humidity outdoors and the a/c warming the room to 21°C.
@@TimAndKatsGreenWalkIs it, maybe, an air circulation problem causing damp and condensation?
@@FoxInClogs I don't believe so. The AC units circulate the air pretty nicely and we don't have any damp/mould issues anywhere. The only condensation problems we have are on our metal framed windows (I hate them), usually only really our bedroom windows. If I could change those frames that'd help a lot but it'd be extremely costly. I'm considering other ways to reduce that particular problem (e.g. linings on the inside of the window frames) but that is ongoing at present.
Dehumidifying the indoor air also helps to reduce the dust mites, which can be helpful if you or your family have a dust mite allergy.
I did not know that. Good to know!
So different from living in the Prairies! We are humid in the summer and super dry in winter.
Yup, good old UK.
That's easy: Dehumidifier, our 3x3.5 m server room had 2 x 2200bts aircons, the humidity was often over 75%, it was not until we got a dehumidifier that it came down to 45-60%
That's a very different use case to mine.
Sounds like oversized AC (I'm guessing you meant 22,000BTU not 2,200BTU). For the size of the room, one likely would have sufficed (and might have even been oversized on its own).
For AC's to dehumidify, they need to be actively cooling - i.e. compressor running outside. If the compressor is turning on and off because the room is already cold enough then they won't dehumidify effectively.
Makes sense. Thanks for the Vid.
No problem.
Dehumidifiers help prevent flea infestations, as fleas can’t survive below 50% humidity-better than toxic spot-on treatments.
Also good to know!
so would you run the dry mode in the summer then to avoid adding more heat into the room
Generally I'd run it in cooling mode in the Summer, as required, but mostly to reduce the temperature rather than the humidity. And even then we use it pretty rarely in cooling mode, only usually when we get a bit of a heat wave. We tend not to have a humidity problem in the Summer, thankfully, it's usually from about Oct to April that we need to run the dehumidifiers at all. Dry mode is essentially just a low power version of cooling mode, so I'm not really sure it should count as a whole separate mode, to be honest!
A heat pump that has a dry vs cool mode doesn't differ in functionality if you need to cool the house anyway.
The only difference between cool mode and dry mode is that in cool mode the unit will either turn off or just run the fan once the inside temperature is low enough and in dry mode if it gets too cold inside it will run the cycle in reverse a bit to add the heat that was previously removed back in to the house.
In both cool and dry mode when it is removing heat the inside unit will get condensation on it which gets removed from the house by either pump or gravity.
Hi Tim , great video, I am thinking of getting a dehumidifier.
One thing, you say you use on your cheap rate during the night.
Is this a special feature on the unit or do you just push the on button and use a timer, Jamie
Ah, good question. I use smart plugs with a timer that turns them on at the time I specify (I have the GivEnergy smart plugs which show up in my GivEnergy app). The dehumidifiers themselves don't have a timer function, sadly (although some might, I've not checked).
I have both types of de humidifier. With the desiccant type, smart plug is ok to turn it on but not off. The instructions warn you to not turn it off at the plug because it needs to cool down using its fan for a couple of minutes. It is also much more efficient in colder temperatures.
With the compressor type, the smart plug is a great way of controlling it. It is much more efficient above 15C or so. Forget it below this temp.
What you could do is, use dry mode when the outside unit does its defrost cycle.
You can't do anything while the outside unit is doing its defrost cycle unfortunately, because it's busy doing the defrost cycle and shuts down all the indoor units. And that only takes about 5 mins, so wouldn't be particularly effective anyway.
Does the AC unit have a drain for the condensed water if using the dry mode?
Yes, there's a condensate pipe that runs to the outside from each of the indoor units.
How does a desiccant dehumidifier prevent the water from being released back into the air when it heats the wheel?
It blows room temperature air onto the wheel to condense it.
I'm not super clear on the details but it looks like the question has already been answered!
Have you thought about Positive Input Ventilation ?
I'd prefer MVHR over PIV, but yes, some sort of MVHR system is something I'd like to investigate further, for sure.
@@TimAndKatsGreenWalk it's very effective, I have mvhr and it keeps humidity below 60% all the time, sometimes under 50%
There is another type of dehumidifier which uses semi-conductor technology called a Peltier dehumidifier. So again no refrigerant, allowing them to be smaller.
My wife bought one from Aldi this week and according to the manual uses the technology.
However, I have to say I'm not impressed - it's very slow to collect water and apparently the most inefficient type of dehumidifier. It just doesn't compare to my Ariadry (same model as yours) which I got very cheaply secondhand a few years back.
Interesting, I'd not heard of that type of dehumidifier before. Sounds like it's not worth bothering with if it's so inefficient. Interesting nonetheless.
Peltier's are notoriously inefficient and get less so as the temperature difference between the plates increases.
I have a 12V insulated cooler/heater that uses one that I use for food delivery. It uses about 4 times the power that a compressor based cooler would use... But there are no reversible compressor based portable coolers that can get hot inside.
So, like most tools they have some uses, but the trade-offs are so much in this case other options are almost always better.
One advantage is that it could be completely silent. Compressor based dehumidifiers are notoriously noisy, especially cheap ones.
Did you consider PIV ?
i.e. filtered tepid air in which finds it's own way out at minimal power consumption.
I just fitted one in my loft to see how it goes - immediate changes are a fresher/brighter? (not sure how to describe it) feel to the air without being particularly colder.
It may even help stop stratification of Aircon air in the stairwell.
My house is not suitable for a full blown MHVR, it's the age where finding holes/sealing it in any reasonable way just isn't possible without some sort of major rebuild!
I'd prefer MVHR, really, so that's what I'm looking into at the moment. In particular single room options that might suit.