Heat Recovery And Cooling In Biogas Chp Systems August 4, 2026 Combined heat and power (CHP) systems are central to most commercial biogas operations. They convert methane to electricity and capture waste heat for productive use — and they create a thermal management challenge that must be designed thoughtfully. Understanding how heat recovery and cooling interact in a CHP system is essential for maximizing energy efficiency and maintaining reliable operations across seasons. How CHP Heat Recovery Works A biogas CHP engine-generator produces two useful outputs: electricity and heat. The heat comes from two main sources: Engine jacket water: the engine cooling system captures heat from cylinder walls and heads, producing hot water at 180-210 degrees F. This high-grade heat is the primary source for digester heating in most facilities. Exhaust heat: engine exhaust exits at 900-1,100 degrees F. Exhaust heat exchangers (economizers) can recover additional heat as hot water or steam. Combined jacket water and exhaust heat recovery can capture 70-80% of fuel energy that would otherwise be wasted. The Seasonal Thermal Balance Challenge Season Thermal Management Situation Winter Digesters need significant heating; engine waste heat often fully utilized; little or no cooling needed for heat rejection Spring/Fall Digester heating demand moderate; partial heat utilization; some excess heat to reject Summer Digester heating demand at minimum; most engine waste heat is surplus; significant cooling capacity needed for heat rejection and equipment cooling "The CHP thermal balance is a year-round design challenge. You're not just designing for winter heating — you're designing for summer heat rejection too, and in many climates that's the more demanding scenario."— Andy Backer, VP of North American Sales, G&D Chillers Options for Managing Summer Heat Surplus When engine waste heat exceeds digester heating demand, facilities have several options: Chiller plant: uses the surplus heat rejection capacity to produce chilled water for facility cooling, process cooling, or gas conditioning — converting the problem into a useful output Cooling tower: rejects excess heat to atmosphere through evaporation; simpler and lower cost than a chiller but provides only heat rejection, not useful cooling Engine load reduction: reducing engine output reduces heat generation but also reduces electricity production and revenue; typically not the preferred solution Absorption chilling: uses engine heat directly to drive a thermally-activated chiller; highest efficiency use of waste heat but requires significant capital investment System Integration Design Effective CHP heat recovery requires integrated system design across the heating loop, heat exchangers, cooling circuit, and controls: The heating loop must be sized to transfer maximum engine waste heat to digesters under coldest conditions Heat rejection capacity (chiller or cooling tower) must handle maximum surplus heat under hottest conditions Controls must manage the transition between heating-dominant and cooling-dominant modes without manual intervention Engine backup heating (natural gas boiler or equivalent) must be sized for periods of engine downtime Frequently Asked Questions How much of the fuel energy in biogas can be captured with full CHP heat recovery? A well-designed CHP system with engine jacket water and exhaust heat recovery can capture 70-80% of fuel energy (as combined electricity and useful heat). Without heat recovery, a standard gas genset converts only 30-40% of fuel energy to electricity, with the rest going to waste heat. What is the optimal sizing ratio between CHP capacity and cooling capacity? This depends on your specific thermal loads, but as a starting point: summer cooling load typically equals or exceeds the digester heating requirement. Model the full annual thermal balance before finalizing equipment sizes. > Design your CHP heat recovery and cooling system with G&D -> Contact us