Detailed Analysis of an Innovative Evaporative/Radiant Floor Slab Cooling System

J. Huang, L. Rainer, L. Shen*

*Private consultant.

Evaporative cooling is a low-energy cooling technology well suited to semi-arid climates and moderate cooling loads in California. Despite its potential to reduce cooling electricity use and peak demand by 30-70%, evaporative cooling is not widely used because of general unfamiliarity, high initial costs, concerns about indoor comfort and humidity, and the mismatch between available models and the California cooling requirements.

To address these technical and institutional barriers, the Davis Energy Group, a private consultant company, designed an innovative cooling system coupling a direct evaporative cooler with an underfloor cold water storage system, and installed the system in several utility-sponsored test houses in the Central Valley and desert regions of California. The evaporative cooler is operated at night to take advantage of the low wet-bulb temperatures and remove as much heat as possible from 1300 liters of water stored in 600 meters of plastic tubing below the floor slab.

Figure. Schematic drawing of the night underfloor evaporative cooling system (NUECS).

During the day, the cold water in the tubing provides radiant cooling through the floor slab and can also be circulated through a fan coil unit for more immediate cooling. In addition, the direct evaporative cooler can be used to provide additional cooling when needed. During its first year of operation, one such unoccupied house in Sacramento maintained inside temperatures at below 26°C (78°F) throughout the summer with only the radiant cooling through the floor slab, i.e., without relying on the fan coil unit or the direct evaporative cooler.

We are collaborating with the Davis Energy Group to evaluate the performance of this Night Underfloor Evaporative Cooling System (NUECS). A computer model of the cooling system is being developed, which combines a detailed two-dimension foundation heat flow simulation program with the MicroPas computer program for simulating residential buildings. The computer model will then be used to improve NUECS operations and design and determine its applicability to other climates and building conditions.

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