Humidity Too Much for Existing Equipment

Rosetown’s first step toward relative humidity improvement was the installation of a Dectron Internationale (Roswell, GA), Dry-O-Tron® dehumidifier to collaborate with existing Carrier Corp. (Syracuse, NY) and York International (York, PA) rooftop air conditioning equipment.

While it was a cost-saving answer to air conditioning and heating, the existing equipment couldn’t provide humidity relief. Even though the extra measure of installing a frozen food area return air channel in the existing concrete slab was helpful, humidity still posed a problem. Previously controlling humidity levels in hot summer months in the original store fell well short of the targeted in-store rh goal of 40% to 50%.

While excellent at air conditioning a supermarket space, the existing York 20-ton combined with 69 tons of assorted Carrier rooftop DX (direct expansion) equipment isn’t designed to fight high humidity levels. In attempts to lower humidity, the rooftop equipment instead overcooled the space, which resulted in wastefully activating heating modes when outdoor ambient temperatures were over 70˚F.

To cost-efficiently retain the existing air-conditioning-heating equipment, Rosetown’s president Bill Whitten conceived a strategy of using a dehumidifier to supply dry air in the summer. Before implementation however, Whitten had to decide between desiccant or mechanical technology. Desiccant is more expensive in up-front capital, has higher operating costs, and requires more maintenance vs. mechanical dehumidification in an application of this nature, according to Thomas Kilmer, P.E., president of Kilmer Environmental Inc. (Mississauga, ON). “Mechanical dehumidification cools the make-up air to a dewpoint of 50˚ and then, by using free reheat from the compressor hot gas to warm the air to 75˚, it maintains the rh in the space at 40%,” explained Kilmer. “Desiccant technology is beneficial when you need a very low rh of less than 30%. All that’s necessary in a supermarket application is providing a 50˚ dewpoint, which is easily done with mechanical dehumidification. The excessive moisture removal characteristics of desiccant are designed for far lower dewpoints. So why use an elephant gun to shoot a squirrel?”

Kilmer was instrumental in co-engineering the retrofit’s overall hvacr strategy with Whitten, whose 33-year-old firm specializes in industrial refrigeration and has limited experience with supermarkets. A model RK-40 Dry-O-Tron with a moisture removing capacity of 53 lbs/hr was installed on the roof. Little additional sheet metal work was required since Rosetown removed one existing rooftop unit and connected the Dry-O-Tron directly to the existing roof curb to utilize the existing air distribution system to supply the relocated frozen food aisle.

Finally, the hvacr retrofit also brought the supermarket up to current IAQ standards. Built before the IAQ Standard 62-1989 by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) was established, the store now exceeds the 15 cfm/person required in public spaces. The Dry-O-Tron not only dehumidifies, but it introduces 100% outdoor air to the space. Since the store’s capacity is approximately 100 patrons and workers, the 2,000 cfm provides 20 cfm/person.

Customers Now Shop in Comfort

Longo’s customers probably notice the cosmetic touches of the store renovation first. However, frozen food sales have risen a dramatic 40% mainly because freezer doors are condensation-free, aisle floors are dry, frozen food packaging is frost-free, and customers shop longer in the frozen food because of the air comfort, Wilson said. And, even though frozen food selling space was doubled, the previously nagging problem of high humidity has been eliminated.

Rosetown saved Longo Brothers tens of thousands of dollars in equipment replacement costs by upgrading and incorporating existing rooftop equipment from the supermarket and video store into the retrofit’s hvacr strategy. The retrofit added 25% more space and brought total square footage to 25,000 sq ft while the improved hvacr systems has increased indoor air quality and customer comfort.