Mechanical ventilation (with or without heat/enthalpy recovery) with filters -- what should one look for when evaluating what to purchase? Do you recommend specific brands?
* Do try to get an HRV/ERV if you live in places where the outside air temperature gets >30C or <10C. Otherwise bring in fresh air will cause issues.
* Make sure your system can handle MERV16 filters: they catch more things, but may create more back pressure, so the system has to be designed to handle it. Further nice-to-have upgrades would be HEPA capabilities, and (if you live in wildfire zones) charcoal filters (for smoke/fire smells). You don't have to (always) use the finer filters, but having that option is useful.
* The filter should ideally be 4"/10cm, as they have more surface area, so reduce back pressure and often only have to be swapped every 6 months (sometimes even every 12). They do cost a bit more because of the extra material, but you get convenience. Don't go less that 2"/5cm though.
* The mentioned Zehnder is a good brand, but AFAICT, are higher end systems, and so may be a bit more pricey:
* Consider getting a separate whole house dehumidifier, depending on your climate: sometimes the indoor air temperature may be comfortable (20-25C), but if the relative humidity (RH) gets too hight (>60%) it will feel hot. But the AC won't run because its thermometer will say everything is fine. Temperature and moisture needs to be dealt with via separate mechanical systems.
>Temperature and moisture needs to be dealt with via separate mechanical systems.
Are there dehumidifiers on the market that aren't air conditioners with a bucket under the condenser coils to collect the water? And if you have a whole-house version of one of those, do you need another whole-house air conditioner?
It's a matter of volume: one of the portable ones could be useful in a small apartment/condo, or (if you close the door) a bedroom. But if you have something that is 1000 sq. ft. / 100 sq. m. or larger, you may need multiple portable units. It may be simpler to just install a fixed unit and patch it into your existing ducts.
There's also the fact that you have to empty the portables, so they may stop at 'random' times until you do so. Not sure about their efficiency, given that have space-volume and weight constraints compared to a fixed whole house unit. Plus you have the noise of the unit running in your living space, compared to having it in your mechanical area.
I don't see how what you just wrote supports your assertion that "temperature and moisture needs to be dealt with via separate mechanical systems" or answers my question, "Are there dehumidifiers on the market that aren't [essentially just] air conditioners?" but you don't have to explain if you don't want to.
Yes, a dehumidifier does work on a similar principal as an air conditioner: there's a cold (metal) surface that causes condensation to remove moisture from air as it passes over.
An AC system would then take the heat that is also removed from the air and send it via a refrigerant loop to some place else (usually an outside device). A dehumidifier simply takes the extracted heat to another coil inside itself and reheats the air to (roughly) the same temperature.
The purpose of a furnace is to put heat into air, of AC to take heat out† (which just so happens to also change the RH), and that of a dehumidifier is to remove moistures while not altering temperature.
If your thermostat already reads (say) 25C, but your RH is 70% (e.g., due to a lot of cooking), then it's going to feel much higher than 25C. So do you crank the AC? You drop the temperature down to 20C, but the RH may still be 60%, and still feels too warm/muggy for you. Do you crank it to 18C? Running the AC, even though the thermostat says things are "fine", can use a lot of energy just so you can feel comfortable. There's a reason why the "humidex" / 'feels like' concept is often mentioned in weather reports: it has both psychological and physiological effects (wet-bulb 35C is a real thing).
Also note that, in winter, even if the temperature and humidity are okay, it may still feel too cold because of mean radiant temperature:
MRT is why people feel a "draft" near windows. There is 'extra stuff' going on the walls and windows and thermal bridging. Do a search for ASHRAE 55 for various factors that go into making a comfortable (indoor) environment:
† AC was actually originally created for humidity control by Willis Carrier specifically for printing, to keep the ink and paper consistent and not runny. Cooling humans was only "discovered" as a use case later.
I opted for Zehnder using a DIY package. If you have basic DIY skills you can install it yourself in a couple of days. Comes with semi-flexible ducting, which is super easy to use. I have fresh air delivered to the living room & bedrooms, and extraction in the kitchen/bathroom/utility room. The unit does heat recovery in winter, which ought to save a bit on the heating bill. It's early days, so we'll see how that goes.
