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Refrigeration Defrost Heat Load Calculator engineering
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Refrigeration Defrost Heat Load Calculator

Model thermal energy requirements to melt evaporator coil frost, compare hot gas condensing mass flow vs electric elements, and determine room penalty loads.

Evaporator Coil & Frost Mass

Defrost Efficiency & Cycle Frequency

Thermal Energy & Heating Demand

Total Heat Input / Cycle
-- BTU
-- BTU/hr firing rate
Electric Heater Power
-- kW
resistance element rating
Hot Gas Ammonia Flow
-- lbs/min
-- lbs/hr condensed
Daily Room Heat Penalty
-- TR Load
added to plant refrigeration

Defrost Energy Component Breakdown

Sensible Heat (Warming Frost to 32°F): -- BTU
Latent Heat of Fusion (Melting Ice @ 144 BTU/lb): -- BTU
Metal Coil Sensible Warmup: -- BTU
Parasitic Room Heat & Vapor Escape: -- BTU

Hot Gas Defrost vs Electric Elements

Hot Gas Defrost Advantages: Hot gas introduces heat directly from the inside of the tubes out toward the fin collar, cleanly detaching the frost ice blanket from the tube surface. Electric heating elements warm the outer air and radiate inward, which requires significantly more power and increases air plume convection into the room.

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Frequently Asked Questions

Why is hot gas defrost more energy efficient than electric defrost in industrial ammonia systems?

Hot gas defrost utilizes reject waste heat directly from compressor discharge gas rather than consuming high-grade grid electricity. Furthermore, hot gas condenses inside the evaporator tubes, directly releasing latent heat to break the ice-tube bond from within, causing large slabs of frost to slide harmlessly into the drain pan before fully melting.

Why is defrost thermal efficiency typically only 30% to 45%?

A significant portion of heat generated during defrost does not melt ice. It is absorbed by the heavy steel and aluminum coil metal, warm air convecting off the fin surfaces into the refrigerated room, and heat radiated to room walls and ceiling.

What is the room re-cooling penalty associated with defrosting?

After defrost completes, the evaporator coil metal and warmed air inside the fan casing must be pulled back down from ~45°F to operating suction temperatures (e.g. -15°F). This re-cooling demand adds direct mechanical refrigeration load to the central refrigeration system.

What safety precautions are necessary for hot gas defrost lines?

Hot gas must be introduced gently via a soft-gas valve (slow bleed) to repressurize the cold evaporator coil before the main hot gas valve opens wide. Rapid opening can cause hydraulic shock (condensation-induced water hammer), which can violently rupture ammonia pipes and coil headers.