Direct loop. The circulation makes the floor be the radiator. For a large area, I'm thinking about 180' x 90' it may need supplemention depending on the generator size.
A direct-loop system is the most thermodynamically efficient choice for this application. By treating the 16,200-square-foot factory floor as the primary radiator, you eliminate the energy loss inherent in a heat exchanger and ensure the most immediate transfer of thermal energy from the generator's jacket water to your concrete curing zone.
Given the 180' x 90' footprint, your concern regarding supplementation is a valid engineering consideration. Here is a breakdown of the thermal load and potential ways to bridge the gap.
1. Thermal Load vs. Generator Output
A standard water-cooled diesel or natural gas generator typically rejects approximately 2,500–3,500 BTU per kW of electrical output into the cooling system.
The Math: If you are running a 100 kW generator, you have roughly 300,000 BTU/hr of "free" heat available.
The Demand: For a 16,200 sq. ft. slab in a mountain environment, a typical radiant heat requirement can range from 20 to 40 BTU per sq. ft. to maintain a stripping-capable temperature.
The Gap: Your total demand could be between 324,000 and 648,000 BTU/hr. In this scenario, a 100 kW generator provides a significant portion of the base load but may fall short during peak winter or during a two-pour 24-hour cycle where rapid heat recovery is needed.
2. Strategic Supplementation Methods
To maintain the Fortress Grade production speed without over-investing in a massive generator, consider these "boost" strategies:
In-Line Electric Boiler: Since the generator is already providing electric power, an in-line electric boiler can act as a "trim" heater. It only kicks in when the return water temperature from the slab drops below your target for the high early strength plasticizer to work.
Exhaust Gas Heat Recovery (Combined Heat & Power): You can capture an additional 25–30% of waste energy by installing an exhaust gas heat exchanger. This "supercharges" the coolant temperature before it enters the floor piping, potentially eliminating the need for any supplemental fuel.
Zonal Manifolds: Divide the 180' x 90' floor into zones. Focus the highest heat on the carts that were just poured, while maintaining a lower "holding" temperature in the stripping and prepping areas.
3. Direct Loop Maintenance Considerations
In a direct loop, the water circulating through your floor is the same water cooling your engine.
Corrosion Inhibition: You must use a high-quality heavy-duty engine coolant (EG or PG based) to prevent the slab piping from corroding the engine's internal components.
Filtration: A side-stream "bypass" filter is recommended to catch any particulates that might settle in the large 16,200 sq. ft. loop and eventually clog the generator’s thermostat or water pump.