Home Efficiency

Just some random thoughts and reminders for myself and maybe some others ;)

Building as a system! Everything works together, so every detail and interaction matters.

Take care of the biggest energy waste problems that are cheap to fix first. Every incremental improvement must be evaluated against diminishing energy consumption. Don't be dumb and have your ducts in the attic, or more specifically outside of the building envelope where they don't belong(shame on you builders). True story: Only terrible people build with flex duct. ;)

If you can bring the ducts inside the conditioned space, all the better. Even better would be to get rid of them completely. Going from a central AC unit with ducts in the attic to mini-splits will save you a whole lot of energy. First you don't have to use energy to force the air through the duct system, that is most likely designed and installed poorly in the first place. You also don't have the heat gain and loss through the duct work, which saves even more, which in some situations can lead you to needing 1 ton less cooling. That is significant on it's own as long as your space would work with mini-splits and you don't mind the looks of the wall mounted units or go with a ceiling cassette/floor/ducted mini-splits. With the recent parts supply issues, it may even be more wise to go with multiple mini-split systems vs one central system. That way if one system is down for maintenance/repair/replacement the others can cover most or all of the load while service is being completed.

Mr. Cool has a DIY series that has pre-charged lines that are sealed until you connect them to the units. That allows you to complete your install without having to apply vacuum after connecting the refrigerant lines. Makes the system quite easy to install by any handy person using only basic tools. The hardest part is determining the best place to mount the indoor unit, preferably on an outside wall so the lines and drainage are easy to route. Once you find your location and use the template to determine where you hole is supposed to be, make sure that there isn't a stud, electric, water, etc in the path of where you are going to drill your hole to the outside. Once the hole is drilled and the bracket is mounted to wall studs, it's pretty easy to route the lines/drain/control wires though the wall and mount the indoor unit.

Screw recessed/can lighting through the envelope as well! They leak like crazy, but there are some solutions, none of them exactly cheap, which I need to talk to Chris about.

Low velocity in ducts is great for nice quiet airflow, but also increases contact time with the ducting which increased heat transfer. If you build an efficient home properly and have the ducts inside the building envelope, then the lower velocity is a good thing. But if you have ducts in unconditioned space, more velocity is better to reduce contact time with the ducting which reduces heat transfer. Heat gain in the summer and heat loss in the winter.

Air weighs about 1/10 of a lb for every 1sqft, varies with pressure and humidity, but the point is that it does have weight. High and low pressure areas are at the floor and the ceiling, higher pressure differential = air moves through holes faster at a higher ΔP, not in the middle of the wall. Fix leakage there first, esp those 124 penetrations through the ceiling and at joints.

Undercut doors just don't cut it for return air unless you have very low airflow to that room. Install a jumper/transfer duct/grills for each room that is supplied with conditioned air(other than bathrooms and such). Any excess room pressure causes air to be pushed out and therefore air has to be sucked in from elsewhere. Best to keep it below 3pascals, though most don't have the equipment to measure that, if your AC sucks your door closed then it's probably too much :) This can be done as cheap as a few dollars per grille, 1 for each side of the wall, cut above the door and some scrap 2x4s sealed in there. When combined with a decent undercut door and the gaps around most doors, this is sufficient for most. You can also install light/noise baffles in there if needed. Depending on the way your house is designed/built you may not be able to cut the drywall out on each side above the door for the cheapest method. Jumper ducts are another way of accomplishing the same thing, and they also won't transfer as much light and noise, best for the master bedroom. However if they go outside of the conditioned space, then you will have heat gain/loss to deal with as well. Everything is a compromise.

Insulation doesn't work if air can flow through it, so you should pay attention to and stop the air leaks before adding/fixing insulation.

Lumpy insulation = bad, should be nice and flat. Just a little area with thin insulation allows a lot more heat to transfer and quickly drops the complete assembly r-value.

Insulate/seal that attic access if it's in a conditioned space, or move it to an unconditioned space like I did. That set of pull down steps that aren't insulated are costing you a lot of energy. I completely sealed my attic access and installed a set of pull down stairs in the unconditioned garage. I may add a mini-split to the garage at some point after air sealing and insulating, but it's not a priority at this time.

1ton per 400 or 500sq ft is BS, Do yourself a favor have heating/cooling load calculations done or do them yourself. Check out the trial of HeatCAD and you can do your heating and cooling calculations yourself. As long as you are accurate in your inputs, you will get accurate outputs.

LED bulbs are super cheap, last a long time, and save you on cooling costs as well, any extra heat that is added to the conditioned space has to be moved out by the AC.

I did find an exposed open to an interior wall in the laundry room where they built a drywall shelf for laundry supplies. Nicely hidden by some blown in insulation that looked oddly dirty, because it had inadvertently been an air filter for years. I could feel a slight draft in the adjoining room down where the drywall met the floor, but have finally found the source. A little drywall, some screws, some sealant, and then properly insulating over it fixed that right up.

Speaking of laundry, the dryer exhaust is pulling about 200cfm of conditioned air from the house, so the same amount of unconditioned/hot/cold/humid air will be pulled in through uncontrolled leaks. If you have a window in your laundry room, opening it while running the dryer can help, makeup air from an automatic electric damper would be ideal. Same thing applies to the stove exhaust vent, quite a bit of air going out, should really have a way for makeup air to be brought in close to the appliance.

Humidistat and SPDT relay = change the blower speed. Dehumidify, G connection reduces fan speed/cancel delay. Humidity drops, Y connection for high speed blower w/built-in time delay.

Installed a Nest learning thermostat. HVAC terminals vary, confirm your own.

R = 24vac Hot

RC = Request Cooling

RH = Request Heat

G = Blower

Y = Condenser Cooling

Y2 = 2nd Stage Cooling

W/W2/W3 = Heat, stage 1, 2, 3 etc

C = Common

O = HP Reversing Valve Heating to Cooling

B= HP Reversing Valve Cooling to Heating

S1/S2/T = Outside air temp