The use of low-temperature chilled water also allows spot dehumidification. A 100-percent DOAS pressurizes a building, negating infiltration of outside air. Natural infiltration temporarily can overwhelm the amount of outside conditioned air delivered by a DOAS when a building's outside door is opened, especially in humid climates.

Local dehumidification is needed to overcome temporary infiltration overloads and typically is provided by fan coils installed at building entrances. A fan coil requires chilled water (50°F maximum) to achieve adequate dehumidification, which cannot be supplied by a distribution system using 55°F to 60°F chilled water for radiant panels and chilled beams. With a proper low-flow piping layout, an injection-pumping system can deliver chilled water to building entrances for adequate dehumidification. Additionally, lower chiller operating temperatures (e.g., 40°F to 45°F) allow a DOAS, rather than a direct-expansion unit, to use chilled water.

FIGURE 5. A comparison of peak power demand for a low-flow injection-pumping system.

Figure 5 shows a comparison of peak power demand for a low-flow injection-pumping system. The peak power demand of a low-flow injection-pumping radiant-cooling system is 33-percent less than that of an all-air system. The transport energy for this type of radiant-cooling system is only 20 percent of the total energy of an HVAC system and one-third of the energy of an air system. It combines hydronic heating- and cooling-energy transport with injection radiant heating- and cooling-energy delivery in a conditioned space.

REFERENCES

1. Posko, T. (2008, October). Chilled beams in Chicago. Engineered Systems.

2. Conroy, C., & Mumma, S. (2001). Ceiling radiant cooling panels as a viable distributed parallel sensible cooling technology integrated with dedicated outdoor air systems. ASHRAE Transactions, 107, 578-585.

3. Oleson, B. (2008). Radiant floor cooling systems. ASHRAE Journal, 50, 16-22.

4. Mumma, S. (2001). Designing dedicated outdoor air systems. ASHRAE Journal, 43, 28-31.

An application-engineering manager for Taco Inc., Greg Cunniff, PE, was instrumental in the development of the company's high-efficiency radiant-cooling system. He co-authored the article “Single-Pipe Systems for Commercial Applications,” published in the October 2006 issue of HPAC Engineering.