I’ve been reading on here and doing improvements on my house over the past year and I’m curious about how my temperature profiles compare to others, particularly the slope of the resist line.
Mine is around 0.02. (From -.7 deg/hour to +6 deg/hour over a range from 20F to 85F.
How does this compare to others? Post your profile.
Here’s mine, but the data on the higher temperature range is not very good as I was in the middle of renovations last summer and had some insulation torn out. Once I get another summer’s worth of data, it should look better. My AC did not shut off for about 3 months last summer and as you can see, the cooling line went above 0 at around 85F.
For my variable compressor, variable fan geothermal heat pump, the heating and cooling profiles are not as meaningful as a performance indicator because they do not weight the data by % of heat pump capacity. My heat pump will run for very long periods at very low capacity and fan speed, which from a run time % metric, would not look very good.
House info:
1967 brick ranch 1300 sq ft
2022 work:
Addition of 1000 sq ft for total of 2300 sq ft
2 ton Climate Master geothermal heat pump *with a dedicated water heating mode
Attic and crawlspace encapsulated into the building envelope
New ductwork located in attic with geothermal unit and water heater
Roof insulation:
R28.8 polyiso continuous rigid insulation external to roof deck (2 layers of 2.5" thick sheets, R14.4 each)
R13 Closed cell spray foam on underside of roof deck in the attic
Wall insulation:
Existing walls:
R11 fiberglass batts (I would like to retrofit and upgrade at some point)
New addition walls:
R10 continuous external insulation OX-IS structural insulation
R13 Closed cell spray foam in walls cavities (min 2" thick)
Crawl space insulation:
R5 CMU inserts in block wall foundation
R10 2.5" Borafoam rigid insulation inside CMU wall, around rim joist, between floor joists
Also of note: the slope on my Stage #1 of the furnace flipped this round. I moved the temperature sensor and I am curious if this altered the slope.
House info:
1958 split-level
12 inches of cellulose in the attic
Likely 3 inches of very old rockwool in the exterior walls - zero on the external frame.
3 inch of modern rigid on the basement walls – zero in the crawlspace under the split side of the house
Two-stage furnace (85,000) 80% AFUE
Gas fireplace that is on for about 3 hours a week
Next week I wrap the hot air ducts in the crawl space and measure for rigid insulation. I’ll be opening the walls and refreshing the bedrooms insulation next summer.
I don’t know if I qualify as a High performance house but I will show the result of applying appropriate charge to the AC system (it was low previously), air sealing, along with correcting an air flow issue that was causing high pressure rise to half the house (Manual D is a fascinating reference and helped me improve airflow to the kids room).
From your heat data, looks like you are in a cooler climate that me. I’m surprised you need 3.5 tons of AC for 2400 sq ft. I am in a warmer colmate and my house is 2300 sq ft and I only have a 2 ton AC. It looks like you can cool your house pretty quickly (3-4 degrees F per hour). It must not run very long when it kicks on. Can you share more details of your home construction? Insulation, style, etc. Can some of the experts weigh in?
Fairly standard construction. Stick frame, batt insulation in walls, blown in the attic. House faces east/west. Living Room is 2 stories tall and opens onto loft and hallway for 2nd floor. Carrier 3.5 ton 14 seer AC and 90K BTU 80% furnace.
I am not a professional hvac guy, but I would think if your AC cools at 3-4 degrees per hour when it is >80 degrees outside, it is oversized. If the air temp drops one degree, the AC kicks on, and the house cools by 1 degree in 15 minutes. Then with the AC off, it warms at 1 degree per hour, so the AC is off for 1 hour, then kicks back on again for another 15 minutes. I would think this would not be the best for wear and tear on the compressor. It might also not run long enough to reduce the humidity to acceptable levels. Do you notice any issues related to this? I’m just curious as I learn more.
Not sure if this is the case with your home, but I think too many HVAC companies install systems that are too large and it hurts the homeowner. The first impact is the extra cost of the unnecessarily large system. The second is that the system doesn’t run very long and does not control humidity very well. This leads to discomfort in the home and overall dissatisfaction of the homeowner.
According to my chart at 80 degrees the cooling rate is 2.7 per hour and at 90 it is 1.8. So not as high as 3-4 degrees per hour. My typical cycle is 3 15 minute runs per hour when it is over 90 outside. Humidity stays around 52%. We did have a humidity issue when first installed because the supply vents were blowing so hard the thermostat was satisfied in about 5 minutes because of their location. This was solved by balancing the supply registers, adding a bypass zone to reduce airflow when only one zone was calling for air and adding remote temperature sensors in locations out of direct air flow.
