One of the most difficult building types to find the right balance of affordable construction verses operational and occupant temperature comfort is the warehouse. While generally used for storage, we know people work throughout warehouses and distribution centers (DCS). Providing cooling and ventilation can be a challenge, especially in the climates characterized in the southeastern United States.
OSHA (The Occupational Safety &Health Administration) requires ‘thermal comfort’ to ensure heat stress does not become a danger to workers.
HFA typically recommends increased cooling and ventilation requirements for one basic reason. During our 29 years of business, we have found that increasing the requirements leads to a higher level of productivity from the employees in the warehouses and distribution centers we design. There are various design strategies that can be used to improve thermal comfort and employee productivity to varying degrees while mitigating capital costs including Ventilation with Enhanced Air Speed and Spot and Full A/C Cooling. A warmer, more humid building requires a higher number of employee breaks, so cool down your building for more productive, happier employees.
Ventilation with Enhanced Air Speed
In warm climates that only use ventilation for cooling, we recommend enhancing the air speed. It can lead to increased convective and evaporative heat transfers from the workers which in turn leads to improved comfort conditions. Common warehouse ventilation strategies involve using perimeter louvers for intake and power exhaust fans. This can be a big benefit if placed where it can take in air near the dock doors where most workers spend much of their time. It also ensures air flows from down low near the occupied level up to the roof and out of the exhaust which works with the buoyancy of air.
Supply fans can also be used and may result in fewer wall penetrations. The majority of ventilations designs draw air in from the perimeter and exhaust out the top or make use of a unidirectional arrangement on one side while exhaust is located on the other side. We recommend ventilation rates of 3-6 air changes per hour in climate employing this type of ventilation.
Another common method used to increase air movement is to make use of high volume, low speed (HVLS) circulation fans. HVLS fans can be designed to hit up to 200ft/min of velocity in an occupied zone. To put it in perspective, most air-conditioned offices are designed for 50ft/min or less of air speed. Increasing the air speed to 200ft/min will lower the effective temperature in the space by 7-8 degrees.
Small swivel propeller fans can also be used to ensure tractor trailers receive proper air movement for those loading and unloading the vehicle. Whether large scale HVLS or smaller swivels fans are being implemented, enhancing air speed is recognized as an economically appealing cooling option.
Spot cooling is most effective if warehouse employees have fixed workstations where they spend most of their time. It provides an oasis effect, giving workers heat relief and helping minimize higher break counts and duration. Two main avenues of spot cooling are portable spot coolers and ducted spot cooling for permanent workstations as seen above.
HFA recently provided a client with DCs in Mexico partial cooling of perimeter spaces where the workers spend the majority of their time in the warehouse. Direct expansion unitary equipment was placed on top of lower height parts of the buildings like the shipping office. These units run constantly in the summer months discharging a high volume of condensate that needs proper drainage. For use in the United States, local energy code requirements may require a recirculating unit with heat recovery instead of an outside air unit. Either way,these units can be designed with a smaller tonnage capacity than fully conditioning a warehouse.
Full Warehouse Cooling
In various locations the design conditions for outside air temperature (the area’s projected hottest day, at the hottest hour) can be quite high. A fully cooled building will be needed if a warehouse or fulfillment center decides to retrofit an automated fulfillment system. This automation will add significant internal heat from motor loads and would probably include equipment with limited maximum temperature requirements.
Stay on the lookout for our next blog that highlights the steps to measure environmental heat factors or read the full paper with general requirements here.