Hydrogen Solar Cooling

Ergenics Solar Thermal Heating and Cooling, Inc.

Cooling Capabilities of Hydride Alloys

Reversible metal hydride alloys have the remarkable ability to absorb large quantities of hydrogen and form solid metal hydride compounds.  The chemical reaction is reversible at reasonable temperatures and pressures and the absorption-release cycle can be repeated indefinitely.

The hydride reaction is accompanied by a heat of formation which is exothermic for absorption and endothermic when hydrogen is released, or “desorbed”.  In chemical shorthand, the reversible hydride reactions showing the heats of formation are: 

Absorption:           M + H₂         MH₂ + heat (out)              [1]

Desorption:           M + H₂         MH₂ + heat (in)                 [2]

where M = a metal alloy, H = hydrogen and MH = a metal hydride.

Hydride alloy heats of formation can be used as the basis for heat pump and air conditioning systems. Equation 2 above shows that desorption of hydrogen from a metal hydride is endothermic (requires heat); a hydride heat exchanger cools rapidly and dramatically if it takes the needed heat from ambient temperature water. 

The cooling potential of hydride alloys is extraordinary.  One gram of alloy delivers 158 joules (38 calories) per cycle.  If the cycle time is 15 seconds, 600 grams of alloy (0.2 liters) provides 3513 watts (1 ton) of cooling.