Under “Variable” select “Ave Temp” and under “Summary” select “Mean”
Copy/paste data into spreadsheet tab labeled, “dailyoat” (aka daily outside air temperature)
Find the average OAT for a given meter reading
Example Excel calculation ='Consumption Info'!E1138=AVERAGEIFS(dailyoat!B:B,dailyoat!A:A,">="&'Consumption Info'!B7,dailyoat!A:A,"<"&C7)
Calculate therm use per day in a separate column.
In the end, you should end up with a table like this; though with as many rows as you have meter data available:
Find the linear relationship between temperature and energy use in the house.
Determine baseload. Identify summer months (those with temps greater than 63F OAT). Average the Therm usage for those months.
Determine the heating months (those with temps less than 63F).
Create a table with just OAT for heating only and Therm use/day minus the baseload
Graph OAT heating vs heating use (therm/day)
Find a “best fit trend line” through linear regression.
You should end up with a graph like this:
Determine design load.
Record the slope and intercept in cells.
You’re now able to determine the design load for various temperatures! Multiply a temp by the slope and add the intercept to get expected therm use per day. Convert therms to BTU (x100,000) and days to hrs. Then multiply by the efficiency of your existing boiler/furnace to get the design load in btu/hr.
2.Find ASHP capacity
Look for the number of BTUs per hour that your system can produce at 5, 17, and 45 degrees F. Example: This system has a heating max capacity of 18,200 BTU'S OF HEATING @ 5 DEGREE'S.
Record these in a table. If you will have multiple systems (an easy way to note this is by how many electric meters and/or condensers you'll have), sum the capacities.
3.Compare ASHP capacity to design load of the house
Compare the load to the stated/summed ASHP capacity. If the load exceeds the capacity, you may need a differently sized system or an additional system. If your furnace/boiler is still in good shape, you could retain this as your back up. You could alternatively, use electric resistance equipment as a secondary source for super cold snaps (below design temp).
4. Meeting the building code
The MN building code requires that heating equipment meet the load at defined design temperatures. Make sure your equipment meets this as well when talking with your contractor.