Dear blog, sorry its been a while. But my musing will eventually end up here. Here’s another.

Intro

As a new homeowner in California’s Central Valley this summer, Heating, Ventilation and Air Conditioning (HVAC) has been on my mind a lot. Our 1960’s house has a lot going for it.

Powered Measures:

  • Central air conditioning
  • Gas furnace
  • Standalone air filter
  • Whole house fan

Passive Measures:

  • Attic insulation
  • Double-Paned windows (sorta)
  • Some tree cover
  • External window shades

Variables:

  • Temperature (summer highs routinely hover around 90 Farenheit ± 15 deg)
  • Air Pollution (Particulate matter of 2.5 microns, aka PM2.5, is a pollutant in wildfire smoke)
  • Air Staleness (CO2 deliterously accumulates indoors unless there’s exchange with outside air)
  • Humidity (While there is a comfort range, this is probably the least concerning at the moment)

Costs:

  • Materials
  • Energy

Variables

Temperature

By far the most energy intensive, here are a few charts:

Weather Impact Obviously weather has a a high impact on air conditioning run time. (Both saturdays we were out of town, same with the first of the month.)

Example Day

Graphs from the Ecobee 3 Lite, a nifty smart thermostat. I like it a lot, though at some point I’d like to upgrade to have built-in accessory control.

Moments of note:

  • 3:45am: Whole house fan is activated by timer to bring in coolest air (windows must be open).
  • 6:00am: Whole house fan turns off. Temperature rebounds, probably because of house thermal mass, and warmer air in rooms with closed windows.
  • 6:30am: Manually run whole house fan for a bit.
  • 1:45pm: Air conditioning kicks in.
  • 3:45pm: Thermostat lowers set point to pre-cool house before 4pm, when our PG&E Time-of-Use plan charges us more.
    • We’re going to switch to the 5pm to 8pm rather than the 4-9 option since we work from home.
  • 4:00pm: Thermostat adjusts setpoint up 2 degrees to 78.
  • 7:00pm: Thermostat goes into evening setting at 80 degrees (I have since pushed this back to 9pm).
  • 8:00pm: Open windows, manually run house fan for a bit.

Upcoming temperature experiments will be using a evaporative (swamp) cooler. I purchased an indoor/outdoor one, performance notes will be in an upcoming post.

Air Pollution

Smoke has been a routine issue in California summers. I’ve owned Coway standalone air filter and in combination with having the central air blower run intermittently, it has been more than sufficient at keeping our 1200 sqft. smoke free. To keep an eye on indoor air quality, I purchased a monitor. It’s ok, I haven’t tried to stringently compare it to other sensors and its certainly gone haywire a few times. But it generally maps the Purple Air sensors nearby nearby within 30% or so. On that note, here’s a good primer on Purple Air AQI vs Air Now measurements.

Initially I wanted to add a beefy filter to the central air blower, but the filter insert was pretty small and I am not sure the blower could handle the extra strain. When we upgrade the system, it will have a more performant spec to handle additional air filtration duty.

Another concern is that the whole house fan is on a timer, unaware of the air quality outside. Luckily the delta breeze has been pretty clean and cool, but it is something to keep in mind.

Side note: Cooking is a major source of indoor air pollution as well. The range hood was misconfigured to recirculate instead of vent, that has since been fixed. I’ve tried to use our outdoor grill whenever possible, for heat reasons as well.

Air Staleness

This is a bit of a rabbit hole, but my current measurments peg indoor carbon dioxide at around 1200 ppm by the end of the day. That is not great. The whole house fan fixes this at the end of every evening, but it would be nice to a more active measure to keep CO2 levels low. The best solution for this would be a Heat Recovery Ventilator(HRV) which could exhaust from the master bath (since it lacks a vent) and could feed fresh filtered air back into the the central air distribution ducts with minimal heat loss.

Plant-based staleness remediation needs more research, but a cursory review of the literature indicates that it would require an impractical ammount of plants under ideal lighting situations to make a dent in carbon dioxide levels.

Humidity

As mentioned, not an issue at the moment, except in the master bath where there is no powered vent, just windows. But its dry enough here that mildew is not a problem. It will also come into play with the swamp cooler, as the effectiveness is dictated by Relative Humidity (RH).

Evap effectiveness

Closing thoughts and future directions

Next up will be experimenting with the swamp cooler. Further down the line the older air conditioner and furnace will be replaced with a single heat pump. It briefly crossed my mind, since the back yard is totally barren at the moment, to go for a ground-source approach but I don’t think I have the bandwidth for such a project. For more passive upgrades, the windows and attic insulation can be updated as well.