|Ron Chapek | Director of Product Management/Enterprise Software
Emerson Commercial & Residential Solutions
I recently participated in an article for Winsight Grocery Business, which discussed the importance of keeping refrigeration and HVAC systems in harmony. Click here to read the full article.
Refrigeration and HVAC costs are among the biggest operational expenses a supermarket faces. The reasons? People create warmth. Refrigeration creates cold. Humidity creates wetness. And in supermarkets, HVAC systems constantly struggle to maintain the right temperature and humidity for people, equipment and products. With proper management and planning, supermarket operators can balance these factors and even optimize HVAC and refrigeration systems to work in coordination with each other.
The battle between HVAC and refrigeration
In most buildings, the job of an HVAC system is to maintain a comfortable indoor temperature for customers and staff. But HVAC systems face unique challenges in supermarkets. Coolers, refrigerated display cases, freezers and other units (particularly those without doors), pour cool, dry air into stores. This isolated cold air stresses HVAC systems year-round, as they have to increase heating during winter — burning a lot of energy — while leaving uncomfortably cold spots, even in summer. Your refrigeration equipment alters an HVAC load in ways most systems aren’t designed to handle.
Adding doors or replacing open units can reduce both the load and energy costs. But adding doors creates a different problem: they often fog up — which forces shoppers to open the doors to see what’s inside — defeating the whole purpose of having a door. Fog and frost occur when humid weather, steamy shoppers and chilly air collide.
A foggy situation
Door fogging is a symptom of a very tricky problem: keeping in-store relative humidity (RH) at the proper percentage. If humidity is too high, doors fog over and cooling coils frost up, forcing units to overwork. If the humidity gets even higher, water can condense on floors, walls and even dry-goods packaging. But if the RH is too low, the overly dry air can shorten the shelf life of fresh produce or wilt it.
Almost all the humidity inside a store comes from moister outside air, and it’s up to HVAC systems to lower that humidity to a slightly dry 45 percent RH — and that’s not easy.
The simplest way to do this is to super-chill incoming outside air, because as air cools, its humidity drops. But this wastes energy in two ways: it increases the refrigeration load on the HVAC and can chill the entire store. So, the air first has to be reheated before entering the store, producing yet another energy expense.
Another option to use a desiccant system in the HVAC unit to remove moisture. These systems are effective and reliable, but they require a lot of energy, especially for large spaces like supermarkets.
The article describes a simpler, cheaper solution. The compressors on your refrigeration equipment generate a lot of heat as they compress refrigerants. This excessive heat is usually vented outside the building, wasting a source of free heat. Today, systems can recycle, treat and mix this hot air to create ideal store temperatures and RH — at much lower overall costs.
Advanced systems harvest excess hot air in various ways. Some use the hot vented air instead of the HVAC heater to reheat super-cooled, dehumidified air and reduce reheating costs. Some systems use heat exchangers to recycle the vented hot air to heat a supermarket during cold weather. “Single-path” systems super-chill a limited volume of humid outside air to dry it, then mix it with uncooled air to produce just the right temperature/RH mix. Another system uses two cooling coils, one to cool the hot air as it’s being vented outside, so it can mix with outside air to reach optimal temperature and RH. The incoming air needs little heating or cooling as it reaches the second coil, which greatly reduces the workload on the HVAC system.
Instead of adding to your HVAC system’s workload, your refrigeration equipment can actually help reduce the load, lower your costs, and create the ideal climate for shoppers, employees and facility managers.