A heat recovery chiller is a refrigeration system engineered to simultaneously produce chilled water for cooling and hot water for heating by capturing the waste heat normally rejected during the refrigeration cycle. Rather than dumping condenser heat into the atmosphere through a cooling tower, the system redirects that thermal energy to useful heating loads such as domestic hot water, space heating, or process heating. This dual-purpose operation allows a single piece of equipment to serve both sides of a building’s thermal needs at the same time, delivering substantial energy savings compared to running separate heating and cooling systems.
Technical Details and Performance
Heat recovery chillers operate on the same vapor-compression refrigeration cycle as conventional chillers, but they incorporate a heat exchanger (often a desuperheater or a full condenser heat recovery loop) to capture rejected heat at usable temperatures. Key performance specifications include:
- Coefficient of Performance (COP): When operating in full heat recovery mode, total system COP can exceed 6.0 to 8.0 when both the cooling and heating outputs are counted, compared to a typical chiller COP of 4.0 to 5.5 for cooling alone.
- Chilled water supply temperatures: Typically 40 to 45°F (4 to 7°C), consistent with standard chiller plant design.
- Hot water supply temperatures: Generally 110 to 140°F (43 to 60°C), suitable for domestic hot water preheating, radiant floor heating, and reheat coils. Some specialized units with cascade or two-stage compressor designs can reach up to 160°F (71°C).
- Heat recovery efficiency: High-performance systems can recover 80% or more of the heat energy that would otherwise be wasted.
- Capacity range: Units are available from roughly 20 tons for light commercial buildings up to several thousand tons for large campus or industrial installations.
Common Applications
Heat recovery chillers are most effective in facilities with simultaneous or overlapping heating and cooling demands. Typical installations include:
- Hospitals and healthcare facilities that require year-round domestic hot water and cooling for surgical suites, labs, and imaging rooms.
- Hotels and resorts with continuous hot water demand alongside comfort cooling loads.
- Data centers that generate constant cooling loads, where recovered heat can serve adjacent office or warehouse spaces.
- Aquatic centers and swimming pools that need pool water heating concurrent with dehumidification cooling.
- University and district energy plants serving mixed-use campuses with diverse thermal profiles.
Relevant Standards and Codes
ASHRAE Standard 90.1 (Energy Standard for Buildings Except Low-Rise Residential Buildings) encourages heat recovery strategies and may provide energy cost credits for systems that reclaim condenser heat. ASHRAE Guideline 22 addresses instrumentation for monitoring chiller plant performance, including heat recovery configurations. Additionally, green building certification programs such as LEED award points for energy optimization strategies that incorporate heat recovery chillers.
Practical Significance
By eliminating or reducing the need for separate boilers or electric water heaters, heat recovery chillers lower both energy consumption and carbon emissions. They also reduce cooling tower loads, which cuts water usage and associated maintenance costs. For building owners and engineers, the key to maximizing return on investment is ensuring that simultaneous heating and cooling loads are well matched. When load profiles align, payback periods of two to five years are common, making heat recovery chillers one of the most cost-effective strategies for improving overall HVAC system efficiency.