Zondits Interview with Freeaire®Valerie Eacret for Zondits, June 30, 2014
Killington Resort is a six-mountain ski area in Vermont and the largest in the eastern U.S. The resort recently installed the Freeaire® system, which allows outside air to cool the ski lodge’s walk-in coolers when it is colder than the cooler’s setpoint. Freeaire has taken the idea of free cooling, which is commonly used in HVAC units, and translated it into free refrigeration. Both processes use cold outside air when available to replace cooling with an energy-consuming compressor. While it’s surprising that this idea isn’t already as prevalent in the refrigeration market as it is in the HVAC world, we’re glad that Freeaire has led the way to efficient refrigeration. Zondits decided to investigate the technology and talk with Richard Travers, inventor of the system. Richard took some time to discuss details of the system with us.
Z: What is the Freeaire system and how does it differ from conventional cooling systems?
RT: A Freeaire refrigeration system is actually a way to efficiently control the various components of a conventional commercial refrigeration system used in walk-in coolers and refrigerated warehouses.
It is also a way to replace as much of that compressor-based cooling as possible with clean, efficient, renewable polar energy. This can be thought of as the absence of its more recognized mirror image: solar energy. Polar energy peaks in winter and is the most powerful and plentiful source of refrigeration ever created, delivered by Mother Nature to our doors for months at a time, and, like the sun’s rays, totally free for the taking.
Whenever the outside air is only 4°F cooler than the air within a refrigerated space, simply filtering that air and moving it to the inside with a Freeaire Polar Power® package is a more efficient means of cooling than operating a compressor-based system. When the temperature difference is 40°F, a Freeaire outside air system can be 10 times more efficient, and more powerful, than the conventional system that cools the space during warmer weather. When it is not needed, the entire compressor system, including the evaporator fans, is idle and waiting for the return of warmer weather. The transition from one form of cooling to the other is seamless and allows maximum use of polar energy before resorting to mechanical cooling.
Z: In addition to using colder outside air for cooling, what other mechanisms or technologies does Freeaire use to create energy savings?
RT: A Freeaire system makes sure that each component of the refrigeration systems operates only as much as necessary to maintain optimal conditions, thus ensuring maximum efficiency.
Most refrigerated spaces have evaporator fans inside that operate constantly, 24/7/365, even though they only have to run when the compressor is operating or during a defrost cycle, typically less than half the time. The rest of the time they are just vastly oversized circulating fans. All the electricity used to operate their motors becomes heat, which then must be removed from the space by running the condensing unit. A Freeaire system stops the evaporator fans soon after the setpoint is reached and the compressor stops. The cold is already inside the space, and the goal is to make it last as long as possible before the compressor starts again. To maintain an even temperature throughout the cooler and prevent thermal stratification resulting from the evaporator fans being stopped, we operate one or more low-wattage, high-volume circulating fans in their place, usually using only about 10% as much electricity. This is a savings strategy that is effective at any time of the year.
Similarly, door heaters that prevent condensation on reach-in doors, allowing good visibility of the products stored inside, are often energized constantly. Freeaire uses a digital humidity sensor to not only switch the door heaters off when the relative humidity is too low to cause a problem, but it also uses “pulse width modulation” to apply only as much heat as necessary to prevent condensation.
Evaporator coils that operate at below-freezing temperatures will need periodic defrosting to ensure proper operation. Freeaire uses a “smart defrost” method in which only as much energy and time as necessary are used in defrosting the evaporator coils before returning to normal operation.
Many older evaporator fan motors have shaded-pole or permanent split capacitor (PSC) motors that use 2 or 3 times as much energy as the more modern electronically commutated motors (ECMs) found in newer evaporator fan units. Although evaporator fans run much less often with a Freeaire system, it is a good idea to upgrade older evaporator motors to more-efficient ECMs at the same time as the Freeaire is installed.
Z: Can you describe the advantages of the system in different climates? Does the system provide savings in all climate types or only in cold climates?
RT: Evaporator fan and door heater control, ECM evaporator fan motors, and smart defrosting save energy in any climate, at any time of the year. Sometimes the payback period for these measures is faster than for using outside air, as the installation costs can be much lower.
Using outside air for cooling can also be quite effective in a warm climate when the space is often kept at a higher temperature than the outdoors. This is the case with server rooms that are otherwise cooled with air conditioning units. ASHRAE has recently expanded the window of acceptable temperature and humidity conditions for various classes of computer and server room equipment, making Freeaire systems even more effective in warmer climates than before.
Z: What are the size ranges of Freeaire’s coolers and freezers?
RT: Typically, a cooled space of at least 1,000 cu. ft. is considered the smallest appropriate size for a Freeaire system in the northern United States, although a colder climate, a higher than normal cooling load, a generous utility incentive, and a higher electric rate can all make a smaller cooler cost-effective.
Our Polar Power packages consist of intake and exhaust units that come in two sizes: a commercial package that moves about 500 cu. ft. of air and an industrial package that is four times as powerful and moves 2000 cu. ft. of air. Multiple Polar Power packages can be combined to cool larger spaces. Freeaire systems can be used in refrigerated warehouses with hundreds of thousands of cu. ft. of space.
Z: Do you sell packaged units with the cooler, fans, motors, and controller, or retrofits of existing coolers?
RT: Freeaire sells our Polar Power packages, CircTM fans, an electronic Cooler ControllerTM, and the components to tie in to and control conventional systems in either existing or new coolers. We work with independent contractors who sell and install Freeaire equipment for customers in their area.
Z: What are the cost and financial savings that a typical Freeaire customer will see?
RT: Energy and cost savings increase as the size of the refrigerated equipment and space increases. A typical medium-sized (2,500 cu. ft.) cooler in a convenience store in Vermont can save about 15,000 to 20,000 kWh of electricity annually with a Freeaire system. A 400,000 cu. ft. beer warehouse in the Albany, NY, area is estimated to save about 278,000 kWh each year.
Z: How does the cost of Freeaire compare to conventional systems?
RT: Installing a Freeaire system with outside air does not replace a conventional system, since there will always be times when the outside weather is too warm to cool the space. While a Freeaire Cooler Controller does replace a thermostat and a defrost time clock, we usually recommended installing both systems of control so that either is available when necessary. With “fail-safe” wiring, a problem with Freeaire’s electronic controller or digital sensors can lead to an automatic transfer of control to the back-up thermostat. Such redundancy can provide peace of mind to an owner of a walk-in cooler.
Freeaire systems are usually purchased for their expected energy savings and to extend the life of the conventional equipment. With utility rebates often covering 20%‒60% of the cost of a system, and the installed cost of a complete system ranging from $6,000‒$50,000, the payback period a customer typically sees just from reduced electric bills is from 1 to 5 years.
Z: What are some other benefits and features of Freeaire?
RT: Because Freeaire systems can control for humidity as well as temperature, they can help to maintain storage conditions within a user-selected range for each. Humidity can be kept high for produce or to prevent static electricity in a server room. It can be kept low to prevent cardboard boxes from getting soggy.
The Cooler Controller can communicate with a Web interface module that allows access over the Internet to monitor real-time temperature and humidity conditions and equipment status, historical energy use and temperature data, the ability to make changes remotely, and to receive email alerts of problems.
Z: Can you provide any case studies where Freeaire has proven to be especially effective?
RT: Champlain Farms, a chain of convenience stores across New Hampshire and Vermont, installed Freeaire’s system in all of its 38 stores. Freeaire was installed in stores with an average of about 1,700 cu. ft. of cooler space. The controller is able to shut off door heaters, which remove condensation from the glass doors so the product can be seen, up to 75% of the time. The end result was a 47% reduction in energy use by the coolers and less than a 2-year payback period.
Freeaire was also installed in both of Harpoon Brewery’s warehouses, one in Boston, MA, and one in Windsor, VT. These two warehouses totaled over 140,000 cu. ft. and also saw a payback period of less than 2 years. Outside air replaces mechanical cooling about 130 days of the year in the Vermont location, while the Boston brewery sees about 110 days. Like Champlain Farms, Harpoon’s payback period for this project was less than 2 years.
Grafton Village Cheese also installed Freeaire in its two aging rooms, one of which is over 300,000 cubic feet. Cooling energy was reduced by 34% and the payback period was a year and a half, all while maintaining the narrow temperature band that the cheese requires.