22,000 kWh, a Pool Pump, and a Homeowner Who Wants Solar First
2,600 sq ft two-story, built 2006, Charlotte NC. Equipment: 3-ton 13 SEER heat pump with 15 kW electric strip, electric 50-gal tank, and a 1.5 kW single-speed pool pump running 8 hours a day. The homeowner supplies 12 months of bills: 22,000 kWh total; January 2,900 kWh ($340); July 1,700 kWh ($200); April and October about 800 kWh each ($95). She says the auxiliary heat “never shuts off” in January and wants to spend her $15,000 budget either on an 8 kW solar array ($24,000, financing the difference) or on a 16 SEER2 heat pump ($9,500). The auditor measures a 2,900 CFM50 blower door, attic R-11, and duct leakage to outside at 18% of system airflow. No prior audit has been done.
1. Analyze the bills. Separate baseload from weather-driven use, quantify what the numbers suggest, and list what additional data you need before claiming savings.
Read the worked answer
Separate weather-driven use from baseload before recommending anything.
- Baseload. The two mild months (~800 kWh) are the best available proxy for non-HVAC load: 800 × 12 ≈ 9,600 kWh/yr baseload, about 37 kWh/day. For a four-person all-electric house that is roughly double a normal 400–600 kWh/month baseload.
- HVAC. Roughly 12,400 kWh (56%) is weather-driven, and in a Charlotte climate a 3-ton heat pump should not need that much. January at 2,900 kWh combined with “aux heat never shuts off” points to strip heat running well above the balance point.
- The baseload is partly explainable. The pool pump at 1.5 kW × 8 h ≈ 12 kWh/day ≈ 360 kWh/month (4,300 kWh/yr), and an electric resistance tank for four people is typically 4,000–5,000 kWh/yr. That leaves little room for lighting, refrigeration, and standby, so there may be another load worth hunting.
- Data to collect: 24 months of bills rather than 12, current rate and any rate change, occupancy and thermostat schedule, whether the pool pump runs year-round, the strip kW and thermostat configuration, and hourly smart-meter data - which is the fastest way to separate the pool from the HVAC.
- Normalization: use heating and cooling degree days or a change-point regression on the monthly data. With only 12 months, present a range and label the uncertainty rather than a single savings number.
Bottom line for the client: more than a third of her bill is not the heat pump at all.
2. Build a prioritized plan within the $15,000 budget and defend the order. Address the solar and heat-pump proposals directly.
Read the worked answer
Apply the standard order - reduce load, fix distribution, then equipment, then supply.
- Tune-up plus thermostat programming (~$300). Verify charge, airflow, and defrost, and set the auxiliary lockout so strips run only below the balance point. Possibly the largest saving for the least money, and it must precede any claim about new equipment.
- Duct sealing to outside ($1,200). 18% leakage in a vented attic costs money in both seasons; seal and verify to 6% or less.
- Air sealing and attic R-11 → R-38 ($2,500). Cuts both loads and improves comfort.
- Variable-speed pool pump (~$1,300). 4,300 → roughly 1,500 kWh/yr, about $350/yr at her rate, often with a utility rebate.
- Heat pump water heater (~$2,800). Saves on the order of 2,000–2,500 kWh/yr; confirm the location is favorable, since it cools and dehumidifies the space around it.
- Heat pump replacement ($9,500) only after 1–3, and only if the existing unit tests poorly or is near end of life. New equipment on leaky ducts and an R-11 ceiling wastes much of the efficiency gain.
- Solar last, sized to the post-retrofit load. An 8 kW array sized on 22,000 kWh is oversized once items 1–5 remove several thousand kWh; oversizing hurts payback and, under some net-metering rules, wastes the excess.
The sequencing argument is the deliverable: the same money buys far more if load and distribution are fixed before equipment and photovoltaics.
3. How do you present this to a homeowner who has already decided she wants solar? Give the framing you would use and the limits you would state.
Read the worked answer
Lead with her goal, then use her own bills rather than an argument about technology.
- Show the split. “About 800 kWh a month is used before the heat pump runs at all. That is where the fastest savings are.”
- Put the aux heat in dollars. If January is 2,900 kWh and a properly controlled heat pump January should be far lower, the strips are the reason. That reframes a new heat pump as fixing a control problem, not just buying efficiency.
- Offer phases with numbers. Phase 1 under $2,000 (tune, thermostat, pool pump) with an estimated payback; phase 2 envelope and ducts; phase 3 equipment and photovoltaics. Let her choose the pace rather than telling her the answer.
- State the uncertainty. Savings estimates from 12 months of bills are roughly ±25%, and nobody can promise a bill amount. Say so in the report.
- Be fair to solar. It is a good technology applied in the wrong order here; show the math with and without the retrofits, and note that a smaller array on a smaller load may meet the same goal for less money and less roof.
Document the conversation, the assumptions behind each estimate, and the fact that the sequence was presented before she chose. That record protects both of you if the bills do not fall as fast as she hopes.