The Hi-Cool Heat Pump

The objective of ORNL's Hi-Cool research program is the development of an absorption system that will offer significantly higher energy efficiencies than current absorption technologies—30% or more in cooling COP with potential increases in heating performance as well. This level of cooling COP can be achieved by using higher-efficiency cycles and fluids that can be operated to higher peak boiler temperatures. The target cooling gas COPs for Hi-Cool cycles are 1.5 or above for chillers and 0.9 or above for unitary/packaged heat pumps at the 95°F Air-Conditioning and Refrigeration Institute (ARI) rating condition.

Development of the Hi-Cool cycle technology is expected to occur in four phases. The first phase, now completed, involved selection of absorption cycles with the best potential for achieving the objectives. BTC researchers are currently in the second phase of Hi-Cool cycle technology development. In this phase, critical components are being designed, fabricated, tested and developed.

Two cost-sharing Phase 2 contracts are in place with research organizations to develop these next-generation heat pumps. The technologies being developed are

In Phase 3, ORNL will oversee the design, fabrication, testing, and development of a laboratory Hi-Cool prototype heat pump to demonstrate the technical feasibility and thermal performance potential of the preferred cycle. Phase 4 will extend these steps to several packaged prototypes and will also involve a manufacturing cost study and market potential study.

VXGAX Cycle: Specifications for 8-ton light commercial heat pump unit
Cooling capacity (Btu/h): 96,000, ARI condition of 95°F
Heating capacity (Btu/h): 155,000, ARI condition of 47°F
External dimensions (lwh): 604848 in.
Cooling COP: 0.95 at 95°F
Heating COP: 1.55 at 47°F
Electricity: ~ 1.3 kW
Absorbent: aqua ammonia
Operating weight: ~1200 lb
Key features:
  • Single hydronic pump
  • 21-lb ammonia charge
  • Operational to 10°F
  • Three "half-head" solution pumps

Solid-Vapor Cycle: Specifications for 3-ton residential heat pump
Cooling capacity (Btu/h): 36,000, ARI condition of 95°F
Heating capacity (Btu/h): 56,000, ARI condition of 47°F
External dimensions (lwh): 444248 in.
Effective cooling COP:a 1.03 at 95°F (cooling COP of 0.9)
Effective heating COP:a 1.74 at 47°F (heating COP of 1.5)
Electricity: ~ 0.6 kW
Absorbent: complex compounds
Operating weight: ~ 600 lb
Key features:
  • No solution pump
  • High true COPs for both heating and cooling as a result of low parasitic losses
  • High air delivery temperatures (above 100°F) for heating at low ambient temperatures (below 20°F)
  • Simple design with mostly off-the-shelf items
  • Competitive initial and operating cost estimates
  • Single hydronic loop to inside heat exchanger
a Effective COP based on 370 W less electrical power consumption (no solution pump and only one hydronic pump) and a 4:1 energy cost ratio between electric and gas.

For more information, contact

Abdi Zaltash
Oak Ridge National Laboratory
P.O. Box 2008, MS 6070
Oak Ridge, TN 37831-6070

Phone Number: (423) 574-4571
Fax Number: (423) 574-9338

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