Increasing energy efficiency for cold storage buildings
The extreme temperatures required for cold storage buildings requires critical attention to proper insulation and sealing. AIA partner GAF explores what architects need to know about roof assemblies for these facilities.
Cold Storage buildings are designed to maintain cold temperatures, much colder temperatures than a typical building. Having a facility that is properly insulated and sealed to maintain the required temperature and minimize ice build-up is important not only for the products being stored inside, but also for potential energy savings over the life of the facility.
How can roofing materials impact energy savings?
The concept of a cold storage facility is simple; the roof and walls of the structure insulate the products inside. Not having enough insulation, on either the walls or the roof, will make your mechanical systems work harder to maintain the interior temperatures, which increases energy use and can result in higher energy bills.
What about the insulation? The effectiveness of roof insulation is determined by its R-value. The higher the R-value, the better the thermal performance of the insulation and its effectiveness at maintaining interior temperatures. The recommended R-value of cold storage spaces will vary based on the interior temperature, although they are higher than typically recommended for a traditional building.
It is a best practice to install several layers of thinner insulation rather than one layer of thicker insulation to achieve the desired R-value and to reduce thermal bridging. The use of several layers of insulation allows for staggering and offsetting the insulation joints, which blocks the passages that allow for air to bypass the insulation. Limiting thermal bridging can increase energy efficiency as it limits air movement between insulation boards by preventing uncontrolled loss of the interior conditioned air. Better maintaining the interior conditioned temperatures means that the cooling systems are required to run less often, which can equate to energy savings.
What about the roof membrane?
Installing a highly reflective (light-colored) membrane offers benefits when the interior is being cooled, because it will reflect heat from the sun. This will decrease the heat radiating into the interior, which means the cooling equipment will not have to work as hard to maintain interior temperatures.
What about roof attachment?
Thermal bridging can occur where there are fastener penetrations through the roof system, as seen in Figure 1. Fasteners are used to attach the insulation and the membrane to the roof deck, which is referred to as a mechanically attached system. A way to reduce the thermal bridging that occurs at fastener penetrations is to bury them in the system or to eliminate them altogether and install an adhered roof system. An adhered roof system typically fastens the bottom layer of insulation to the deck level and then subsequent layers of insulation and membrane are adhered. This concept is illustrated in Figure 2. By eliminating the fasteners, the path for air to travel into the roof system is reduced.
The devil is in the details
Warm exterior air that meets the cold interior air will condense due to the large temperature differential, and that condensation can turn into ice. Ice can form on various surfaces, including locations where air leakage is occurring, such as at roof-to-wall interfaces, on the floors where the surface of the floor is cooler than the air above it, and within the roof assembly (insulation). Condensation that occurs within the insulation often freezes; frozen insulation provides virtually no insulating properties, decreases energy efficiency, and increases energy bills.
Roof-to-wall interfaces and penetrations must be sealed to prevent air from entering into the roof assembly. The most common method of ensuring sealed terminations and penetrations is the use of a closed-cell spray foam, which is typically installed at the intersection of the exterior walls and the roof insulation as well as in steel deck flutes.
The benefits outweigh the risks
Seemingly insignificant decisions made during the design and construction of the roof of a cold storage facility can impact the functionality and energy usage of the building for the lifetime of the roof system, which is typically 25 to 35 years. The benefits associated with designing and installing a proper cold storage roof far outweigh the risks. A properly designed and constructed roof will save energy, prolong the life of mechanical equipment, and protect both the building’s occupants and the goods being stored inside the facility.
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