Defined goals, had our energy geek model several scenarios, chose a cost-effective approach based on modeling.
General modeling information:
Excel spreadsheet developed by energy consultant.
Outcome of project goals:
Goal was to make home net zero operational energy, including all on-site needs (heating, ventilation, plug loads, hot water). The first year, we were net energy producing. The next year, slightly energy consuming. On average over the past 5 years, we have been net consumers by 390 kwh, or about 5% of all the energy used by our home. (So on average we are 95% to ZNE.) We have had to replace both ASHPs, due to corrosion of coils likely caused by non-expert installation - we may have suffered inefficiency in the past few years due to ASHP performance degradation. An important lesson learned: Hire a very experienced and thorough ASHP installer!
Another interesting lesson learned: We conducted an initial blower door test with 2 blower doors, one on our unit and one on the other duplex unit. When we did air sealing, one blower door was used to monitor improvement, which appeared to be substantial. Subsequent to that, we had the old heating and ventilation systems removed and the new ASHPs and HRV installed. A subsequent blower door test with 2 blower doors showed greater leakage than before we started the renovation. Likely the mechanical renovation did this, or was there some other explanation? Somehow, we were still ZNE, but maybe we just oversized our PV system. We are overdue for some more investigation of leaks and air sealing (unless it turns out the last test was somehow faulty).