REM Engine and calculation procedures
The REM Calculation Engine was developed via a climate similarity analysis by Architectural Energy
Corporation. The REM Engine consists of seasonal generalized heat balance equations that were
generated and tuned via the climate similarity analysis. In the climate similarity analysis, seasonal
weather variables were synthesized from TMY hourly weather data. The REM engine uses the seasonal
heat balance equations combined with the seasonal weather data to calculate loads for each portion of
the house. The engine calculates heating and cooling loads for the following components:
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Ceilings
Rim/Band Joists
Above Grade Walls
Foundation Walls
Doors
Windows/Skylights
Frame Floors
Crawlspace/Unheated Basements
Slab Floors
Infiltration
Mechanical Ventilation
Ducts
Active Solar
Sunspace
Internal Gains
The combination of these component loads totals the annual heating and cooling load for the home.
The REM Engine will also run through a series of set calculations based off of ASHRAE Fundamentals to
determine the peak heating and cooling load for the home. Once again, a peak load for each
component is calculated and the sum of all components is the peak heating or cooling load.
Once the annual heating and cooling loads are calculated, REM will post process the loads to determine
the annual heating and cooling consumption based on the HVAC equipment. Hot water loads are based
off of 42 gallons per day of hot water consumption for the Washington version of REM/Rate. Our
standard version of REM/Rate uses 30 + 10 * ( Bedrooms + 1 ) gallons per day for hot water
consumption. REM cannot determine how a piece of equipment will operate at a given hour or time of
year. REM is a seasonal tool developed for quick and accurate annual energy modeling through
seasonal performance and calculations. Utility rates entered for the home allows REM to calculate the
annual heating, cooling, water heating, lights and appliance costs based on annual energy consumption
for each end-use.
All HERS, ENERGY STAR, IECC compliance are determined by comparing the design home to the
reference home. Once the design home and reference home are compiled in the REM Engine, the
results for each are calculated as described above. The results are compared to determine compliance.