Refrigerated Display Case Load and Internal Electric

With the internal electric load priced as what it is: heat. Every watt consumed inside the refrigerated envelope has to be removed twice -- once as electricity paid at the meter, once as heat paid at the compressor -- at 3.412 BTU/h per watt. Case lights, evaporator fan motors, anti-sweat heaters, and defrost therefore cost roughly their own wattage again in refrigeration, and on a low-temperature case the compressor's poor efficiency at low suction makes the second payment worse than the first. That is why LED retrofits and anti-sweat controls pay back faster in refrigeration than the lighting arithmetic alone suggests, and it is why the retrofit line here reports the meter saving and the load reduction side by side. On an open vertical case the infiltration term through the air curtain is usually the largest single line and the hardest to improve without doors, which is the real argument for doors -- but which of the four terms is largest depends on the case, so this reports the split rather than asserting it. Infiltration and transmission are ENTERED per foot from the case manufacturer's published data, because they depend on the air curtain design, the discharge velocity, and the store's own humidity in ways no per-foot rule of thumb captures. It does not model the air curtain, size the evaporator or the rack, or compute the compressor power at the suction condition. The case manufacturer's rated load and the refrigeration engineer of record govern.

total = infiltration per foot x length + transmission per foot x length + product + internal electric, with the internal electric summed at each term's own run fraction and converted at 3.412141633 BTU/h per watt.

The display-case load summed as ASHRAE Refrigeration practice writes it, with the watt-to-BTU/h conversion exact by definition. Infiltration and transmission are ENTERED per foot from the case manufacturer's published data, because they depend on the air curtain design, the discharge velocity, and the store's own humidity. It does not model the air curtain, size the evaporator or rack, or compute compressor power at the suction condition.

A sum of four terms and one exact unit conversion.

Estimate. AHJ and licensed professional govern.

Field names used by the API: case_length_ft, infiltration_btuh_per_ft, transmission_btuh_per_ft, product_btuh, lights_w, fan_w, antisweat_w, antisweat_run_fraction, defrost_w, defrost_run_fraction, retrofit_lights_w, retrofit_antisweat_run_fraction, infiltration_btuh, transmission_btuh, internal_electric_w, internal_btuh, total_btuh, internal_pct, retrofit_total_btuh, meter_saving_w

• Infiltration and transmission are entered per foot they depend on the air curtain, discharge velocity and store humiditythe case manufacturer's published data
• Run fractions are entered anti-sweat and defrost duty vary with control strategy and store conditionsthe store's own controls
• It does not compute compressor power a low-temperature suction makes the second payment worse than the firstthe rack manufacturer's performance data