I have a CO2 detector that I believe is a reasonable proxy for stale air. When it goes above 1000 I simply open the windows. By the time I remember to close the windows the reading is almost always below 500.
That seemed like the easiest thing to do without making much more complicated system. Basically risk 1hour of bad air for 23h of "clean" air.
I was responding to a comment that presupposes the need for fresh air. If you don't need that, feel free to close the windows then.
Following the thread of conversation, it just didn't compute to me:
>>>> Heat pumps are great for climate control >>> Yeah, ducts are dead >> What if you want to recirculate air in your house through your central air filter to eliminate smells? > Just open the window
It's like we've hit a contraction: the premise is that we care about energy but the contractions is then that we don't and we open the window while climate controlling the house. So to me it does seem to prove that in some climates, duct work with a central blower and filter mat not be dead.
Ducts running in an insulated space are sources of huge energy loss.
We've just today had our first snow of the season here in a lower elevation of the Sierra Foothills. It's been chilly for 3 months or so, and our heating is an 'old school' ducted propane furnace. In time, we'll replace it with a heat pump, but not this year. Anyway, we're sensitive to accumulated odors that go with a well insulated, closed-up home in winter.
Every evening, we open three doors in the house to the outside. This is after the furnace has entered its timed 'off for the night' state. We exchange pretty much all of our air for fresh ambient, which is great when we wake up in the morning.
The impact from doing this on our propane bill is undetectable. This is because air, even humid air, has a trivial heat capacity compared to the warm house structure and contents. Those are by far the greatest energy reservoir in our home. Very little energy is lost in a daily air exchange with the ambient.
*edited for typo
I live in Florida, we've used Heat Pumps for as long as I can remember. We also have central air handlers with blowers and ducts to distribute the conditioned air. Mini-splits can _also_ be ducted mini-splits. According to my HVAC geek friend, mini-splits are pretty terrible about humidity control (an important thing in Florida). For proper humidity control you'd ideally have a dedicated set of dehumidification ducts (powered by a central dehumidifier) as well. Mix in an ERV and you have the ability to build a fairly air-tight house with _controlled_ ventilation and very efficient conditioning of the air in the house.
I was going to install an ERV system but the payback was not within the life of the equipment.
Someday I’ll build a Passivhaus with a system as you describe.
A great option for keeping CO2 levels down in a house is with an HRV (or ERV) [1] that will heat the fresh air coming in to cycle it throughout the house.
I did not 3D print mine, but ordered it, though as an early adopter, adjustment was required.
> During the warmer seasons, an ERV system pre-cools and dehumidifies; During cooler seasons the system humidifies and pre-heats.[1] An ERV system helps HVAC design meet ventilation and energy standards (e.g., ASHRAE), improves indoor air quality and reduces total HVAC equipment capacity, thereby reducing energy consumption.
> ERV systems enable an HVAC system to maintain a 40-50% indoor relative humidity, essentially in all conditions. ERV's must use power for a blower to overcome the pressure drop in the system, hence incurring a slight energy demand.
In Jan 2023, the ERV wikipedia article has a 'Table of Energy recovery devices by Types of transfer supported': Total and Sensible :
> [ Total & Sensible transfer: Rotary enthalpy wheel, Fixed Plate ]
> [ Sensible transfer only: Heat pipe, Run around coil, Thermosiphon, Twin Towers ]
Latent heat: https://en.wikipedia.org/wiki/Latent_heat :
> In contrast to latent heat, sensible heat is energy transferred as heat, with a resultant temperature change in a body.
Sensible heat: https://en.wikipedia.org/wiki/Sensible_heat
There's a broader Category:Energy_recovery page which includes heat pumps. https://en.wikipedia.org/wiki/Category:Energy_recovery
Are heat pumps more efficient than ERVs? Do heat pumps handle relative humidify in the same way as ERVs?:
This morning it was -5C, so not cold by continental standards, but certainly cold enough.
In the UK recirculating air is very rare. In cases that bathrooms don't have a window (or indeed in new houses where they do) there's an extractor fan, but that just vents the air directly outside.
The only requirement is "2 channel low drift NDIR gas sensor". Cheap CO2 detectors either have zero IR sensors (instead they guesstimate eCO2 using a VOC sensor) or a single IR sensor that requires weekly calibration outdoors or it will just assume that the lowest sensor reading means 400ppm.