Ommm

If you have UFH then you have a massive emitter right there, so worries about cooling area don't really matter. If you have only FCUs (the point of this thread), then you have a limited cooling area. Typically they are much smaller than the kinds of radiators you might install for heating with an ASHP. To follow the 'low temp heating' with a 'high temp cooling' analogy, a smaller radiator with a lower deltaT means you need to ramp up the water flow and extra airflow means more noise to contend with. Maybe that noise is ok, it depends. It's not silent like radiators or UFH. The other problem is that during heating your extraneous heat sources (people, solar gain, cooking, electrical equipment) reduce your heating demand, but during cooling those things still exist and serve to increase your cooling demand. My point was that in humid conditions the dew point temp is high and your cooling ability without condensation is limited. That is typically when you need cooling most, and yet you can't run anything cold for fear of condensation. Also that folks say that a major comfort of A/C is in reducing the humidity levels, which is something you can't do without condensation collection (as you cool the air the RH will go up, until such time as it condenses). I'm sure there's a system design where it makes sense - I don't have a good handle on the numbers here. But I think it's going to be harder than heating.

Does this avoiding the dew point idea actually work? A fan coil has a certain difference between water and air temp. Typically ASHP are rated at 7C. Let's say your room temp is 30C. That's deltaT of 23C. At 80% RH the dew point is 26.2C, so now your achievable deltaT is 3.8C. Assuming a constant heat exchanger area, you need to push 6x as much water per hour and run the fan 6x faster to get the same cooling effect. (Different numbers for different temps/RH) Obviously you can oversize (if you have cooling UFH that's roughly what you're doing). But if the UFH isn't in action a fixed FCU can only go so big, and if the UFH is then the FCU isn't adding very much. It seems quite inefficient to run it that way, especially compared with refrigerant based A/C, where the phase change in the evaporator can absorb a lot of heat. Seems like water is already at a disadvantage and hobbling it further is not going to help.

It's a (brushless?) DC fan controlled by a 0-10V DC speed input, so in theory if you apply an analogue voltage you can have any speed. The controllers are often designed for AC fans which have three mains inputs which you energise in different combinations for slow/med/fast and I suppose they carry that over - makes the displays and UI the same. Personally speaking I'd probably want some control with a slow fan ramp, eg if the thermostat decides the FCU to come on then gently ramp up the fan speed to target, rather than having it click on, and only spin as fast as needed (like the fan in a laptop etc). That's why I think the replacement firmware is useful, because it allows you to program that kind of thing.

Those datasheets look very much like the ones from YESNCER. The controller looks like an off the shelf wifi+Tuya unit. I can't find an exact match out of the many on Aliexpress ('fan coil controller') but it fits in a standard 86mm square switch wall box - on the concealed unit it'll be mounted on the wall in one of those, while in the radiator unit there's a space on the top. They are typically interchangeable - some of them have RS485 so can be talked to via Modbus, although I'm not sure if the register list is published (I bought one from Aliexpress to play with but haven't used it thus far). It's a standard ESP8266 chip inside and there may be third party firmware replacements too (mine is the BAC-1000-ALW which is supported by WThermostatBeca).

Euro pricing: https://netzero.jaga.com/docs/Briza_Net_Zero_Listing_EX.pdf I have a feeling I contacted them in 2021 but can't find any email - maybe I filled in one of those web forms and they didn't get back to me? I don't remember exactly.

Ah, YESNCER have been spamming me every few months ever since I messaged them on Alibaba in 2021 🙂 https://yuexinly.en.alibaba.com/index.html Their horizontal FCUs are between $50-200 depending on the size and options, obviously there's shipping and tax to add to that. Typically they have a basket of options and the price depends on which options you pick and how many units you want, so the price displayed is a bit hypothetical. When I looked they seemed OK - hard to judge quality. If it has the DC motor with 0-10v analogue speed control that's the better quieter motor.

I didn't manage to find a match on a brief look around Alibaba, but Megawave's radiator-style FCUs are a dead ringer for a kind of generic boxy FCU style (Megawave v random Alibaba example), and (for some reason) Chinese heat exchangers are often anodized in blue. So I'd guess they are Chinese, even if I can't pin down the ODM. You could ask Megawave for a datasheet? The thing that would bother me is the noise of the fan, which can vary depending on what kind of motor and controller they have (and is hard to picture the raw dB numbers without listening to it). If it is Chinese, they often have relatively simple electrical connections to the unit (valve on/off/bypass, temperature sensor/thermistor, fan speeds 1/2/3 via mains terminals or 0-10V if an electronically commutated variable-speed DC (EC-DC)) and the wifi module is a drop in third party module. Often on the Tuya smart platform, I wouldn't put a whole lot of store by these units (they are cheap), but at least you have access to the raw connections to do something better if you prefer that.

58dBA, so quite loud to have in your room. Roughly like a portable A/C unit but with proper outside ducting. Might be ok for a kitchen or something, but I wouldn't want it in a living room or bedroom.

Thanks all for the interesting comments. Since I posted the OP I'm gradually developing a strategy: For the bathroom (downstairs), the problem is mostly shower moisture but also we leave the window open for fresh air. Fit a non-counterflow single room MVHR, the current frontrunner is the Vent Axia Lo-Carbon Tempra. This location is very noise sensitive, and so I like that somebody has identified that it seems the fan is just a 24V motor which takes a 0 to 5V speed control input and so it's potentially possible to modify it to fit linear speed control with a slow ramp rather than the fixed speeds (also, I don't like the counterflow ones because changing direction may cause noise from cycling). I have a blocked up 100mm wall opening so it should drop straight in. For the kitchen, there's currently a cooker hood with a recirculating filter. This is useless because we never fry things so it's only pushing damp air straight back into the room. The thinking for this is just a regular extractor (possibly a ducted fan in the loft) for the 10 minutes a day something is bubbling on the hob. There are two bedrooms upstairs and three rooms downstairs, that would be good to have both fresh air for air quality and also cooling. I haven't really come up with a strategy for this; I have two small lofts front and back, and each loft can only reach 3 rooms; I might be able to 100mm duct under the upper floor front to back but that would be complicated. I'm also not super keen on cutting giant holes in ceilings or (stud) walls, especially for noise carrying reasons. Maybe there is some way to combine MVHR (low flow rate) and a ducted fan coil from the ASHP for cooling purposes (recirculated air), or do they need separate ducted systems because the air volumes are so different?

There are only trickle vents on two of the upstairs windows, the rest don't have them. For the 'humidity sensing units' I assume you mean fans, ie cut a hole in the wall? I already have one ceiling and one wall hole in the bathroom (both plugged) and could make a ceiling hole + duct + soffit vent in the kitchen (there's a plugged wall hole but at the opposite end to the cooker). But that wouldn't address moisture/CO2 elsewhere, eg bedrooms? Without a heat exchanger, won't that make any room with a fan cold? (yes I know there are backdraft flaps on cowlings, but they didn't work well in my last property). (basically, moving from a 'window open all the time with cold draughts' model to a 'warm fresh air all the time' model is the motivation to look at MVHR)

I've been challenged to sort out some air quality issues in our 1960s 120m2 chalet bungalow: No moisture extraction in the bathroom beyond a window; there was previously a fan which just blew straight into the loft, with no ducting anywhere No extraction in the kitchen: the cooker hood just recirculates via a filter No effective ventilation upstairs (loft conversion) beyond useless trickle vents, hence window condensation (made worse by good thermal blinds so temps behind the blinds drop overnight) Occupant who suffers from noise and air quality sensitivity - we run room HEPA filters a lot ASHP installed with the possibility of fitting a ducted water fan coil for cooling Tight loft spaces (crawl only, not conditioned) House is quite leaky, especially into the loft (holes for pipes, electrical fittings, access hatches), and some old vent holes (todo to block these). It's a windy area so much more leaky on windy days and less on still ones. Chimney with wood stove (the vents are largely left wide open for optimal burn) I had originally considered going for dMVHR to address the first with a Vent Axia Tempra in the bathroom, but having listed the others wondered about ducted MVHR. I realise we get some amount of fresh air from the leaks (although I hope to plug those) but hope to improve moisture control and air quality. Does central MVHR make sense for this? I suppose I can improve the moisture situation with maybe 3x dMVHR units (bathroom, kitchen, upstairs), then the other rooms have their own leaky ventilation. That doesn't get filtering or cooling, but maybe a central air filter/fan coil doesn't make sense in a leaky house? Maybe the physical limits (not much flexibility in duct positioning in each room) make it ineffective? Cost is a big factor so looking at ebay parts and DIY install (also the physical design constraints are hard to convey), but not really sure how to start with system design. Searching around brings up lots of puff pieces for design services, but not so much about design principles. I did my own ASHP design and there were decent resources for that. Any pointers on how to begin?

Yes it's a water FCU. Here's the specs from the above link. (correction to the above, it's 1/2" BSP water connection) If you're local you're welcome to come and I can demo it (dry) - send me a PM for more details.

Due to a change of plan I have a Daikin FWT05GATNMV1 wall-mounted fan coil unit available, plus a Daikin Merca wired controller. Both are new and unused, with original packaging. I've dry-tested them and everything works as it should. I think it takes a 3/4" BSP water connection. (The cover is not screwed on in that picture, hence it's a little askew). See https://ibb.co/album/QDh90v for more photos. £350 for the pair. Location is Cambs/Beds border - I'm happy to deliver for free within Cambs or Beds or maybe a little further into surrounding counties. Much further afield I can assist a courier that you organise - it originally came either Parcelforce or DHL, I can't remember now, and cost was about £20. While the original polystyrene packaging was enough to get it to me and I have it all, with all the fins and plastic cover it is quite a fragile item so any courier collection would be at your risk.

Yes, they’re the basic Chinese type I posted about a year ago in this thread. See my comments about this specific listing but I have other posts about the Chinese units. The price is about double Alibaba pricing but of course you don’t have to import from China. If you’re going to buy a large number the sea freight and import fees will possibly be worthwhile to buy direct. I have no direct experience since I never ordered any, but I saw that listing about a year ago and decided that particular one would be too small for my application. Also it’s not clear what kind of motor these have: you can get them with basic AC motors but the better ones have DC (electronically commutated or EC) motors - the Alibaba suppliers will do DC but often default to the cheaper AC motors which are louder and less efficient. (I should check whether the motors are available separately on Alibaba - they might well be) One nice thing about this Chinese ecosystem is the controls are usually in a simple back box like a light switch on the top of the unit and are easily swappable, so you can find simple thermostats or wifi/RS485 modules, and change them to get what you want.

What I would be tempted to do is look for the telltale white gunk that's collected around a leak, and then go over it with something stronger. The gunk is just acrylic sealant, so for example filling a void with expanding foam and then putting sealant on top might be sturdier than just the sealant itself. You might also want to think about using something that can flex based on movement, given the spray is only happening at one temperature and it's not clear how well the acrylic sealant will flex with expansion and contraction. Following the radiator leak example, I wonder if they could put UV dye into it so the gunk can be seen more easily? :-)