NIST helps heat pumps 'go with the flow' to boost output

Jan 23, 2008
NIST helps heat pumps 'go with the flow' to boost output
A sheet of laser light illuminating the surface of the heat exchanger during the air velocity measurement experiment. Credit: NIST

Air-source heat pumps typically deliver 1 1/2 to three times more heating energy to a home than the electric energy they consume. This is possible because heat pumps move heat rather than convert it from a fuel (as combustion heating systems do). National Institute for Standards and Technology researchers are working to improve the performance of these energy superstars even further by providing engineers with computer-based tools for optimizing heat exchanger designs.

In a typical air-source heat pump, air flows over two refrigerant-filled heat exchangers (known as coils): one indoor and the other outdoor, both of which have metal fins to aid heat transfer. In the heating mode, liquid refrigerant within the outside coil extracts heat from the air and the refrigerant evaporates into a gas. The indoor coil releases heat from the refrigerant as it condenses back into a liquid. A valve near the compressor can change the direction of the refrigerant flow for cooling.

Performance of air-to-refrigerant heat exchangers can be reduced by uneven air flow distribution. However, performance degradation can be significantly avoided by design changes that increase refrigerant flow in areas that receive more air. To achieve this, one must ascertain the actual air distribution in a given system.

NIST researchers have developed a testing apparatus that uses a high-resolution camera to track—with laser-illuminated dust particles—the motion and distribution of air flow in finned-tube heat exchangers. Data from these highly accurate laboratory experiments are being compared with computer simulations of air flow performed with computational fluid dynamics (CFD) software. Once accurate CFD models are developed and validated, engineers could use them as the basis for design changes to coil assemblies and refrigerant circuitries to accommodate the existing air distribution.

The NIST program, partially sponsored by the Air-Conditioning and Refrigeration Technology Institute (ARTI) under a Cooperative Research and Development Agreement (CRADA), could increase finned-tube heat exchanger heating or cooling capacity by five percent, resulting in improved heat pump efficiency. Additionally, such improvements could allow manufacturers to reduce the heat exchanger size, thereby reducing material cost and the amount of refrigerant needed. The NIST study results on home air-source heat pumps will be issued in 2009 and are also expected to be applicable to large heat exchangers used in commercial buildings and refrigeration systems.

For further information, go to www.bfrl.nist.gov/863/HVAC

Source: National Institute of Standards and Technology

Explore further: Building the world's fastest downhill racer

add to favorites email to friend print save as pdf

Related Stories

What is a heritage turkey?

37 minutes ago

Over 45 million turkeys are eaten by Americans each Thanksgiving, according to the U.S. Department of Agriculture. Hunters provide some—last autumn, about 24,000 wild turkeys were harvested in Pennsylvania. ...

New technology reduces size of spinal stimulator implants

57 minutes ago

Spinal cord stimulator implants could use less power and be made much smaller as work from Taiwan and Israel eliminates off-chip high-voltage devices from the implant's pulse generator. This will reduce implant-related ...

Recommended for you

Tomorrow's degradable electronics

6 hours ago

When the FM frequencies are removed in Norway in 2017, all old-fashioned radios will become obsolete, leaving the biggest collection of redundant electronics ever seen – a mountain of waste weighing something ...

Building the world's fastest downhill racer

Nov 19, 2014

I'd like to say that it's not every day you get asked to try to break a world record with a speed-obsessed truck mechanic from Grimsby, but for us at the Centre for Sports Engineering Research it's starting ...

Recycling Styrofoam into rigid plastic

Nov 18, 2014

Mexican entrepreneurs designed the first machine in the nation capable of recycling Styrofoam (expanded polystyrene) and transforming it into a raw material used in the manufacture of transparent hard plastic.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.