Comparison of construction and energy costs for radiant vs. VAV systems in the California Bay Area
The goal of this study was to perform a design stage cost analysis comparing a selected radiant building against an identical building with a traditional variable air volume (VAV) system. Major findings from the cost estimates include:
• The radiant HVAC design has a total cost of $38.9/ft2 compared to $29.9/ft2 for the VAV design, representing a $9.0/ft2 premium for the radiant design.
• The higher costs for the radiant system can largely be attributed to higher piping labor costs for piping and radiant equipment, which itself is $9.8/ft2 higher than that for the VAV design.
• Since labor rates are higher in the San Francisco Bay Area, for the estimated national average labor rate, the premium for radiant is $6.8/ft2, compared to the VAV system. The high installed cost for the radiant equipment is partly a reflection of the current radiant manufacturers’ pricing strategies and the contractors’ bidding practices. The radiant market is relatively small and immature in the United States, especially compared to the well-established VAV market. Alternative design approaches are discussed that may reduce first costs and/or energy costs. Energy models of the two designs (radiant and VAV) were developed in EnergyPlus to evaluate the corresponding energy and comfort performance. In the VAV system model, the controls are generally based on the recently published ASHRAE Guideline 36 (ASHRAE, 2018), which provides high performance sequences of operation for VAV systems. However, for the hybrid radiant slab and DOAS system, there are no well-established control sequences readily available. The annual simulation results show that the total site HVAC energy use is 16.2% higher for the radiant system (2.9 kBtu/ft2) than the optimized VAV design (2.5 kBtu/ft2). The report contains further discussion of opportunities to improve the energy performance of radiant systems. For example, in mild climates, such as the Bay Area in California, radiant designs should take advantage of the benefits of free cooling as much as possible either with airside or waterside economizers.