Energy Efficiency for Commercial Buildings
Buildings including residential consume approximately 40% of the world’s energy followed by transportation and industry.
On January 1, 2015 the State of Maryland adopted the 2015 International Energy Conservation Code or IECC with adoption and enforcement on July 1, 2015. One tool to determine compliance is called COMcheck which allows the equivalent of ASHRAE (American Society of Heating Refrigerating and Air Conditioning Engineers) Standard 90.1-2013 Energy Standard for Buildings. Maryland and Vermont were the first two states which adopted this standard. As of this writing two additional states, Alabama and New Jersey have adopted this standard.
This baseline standard for high performance buildings has significantly changed how buildings are designed, constructed and operated over the past decade. While various types of buildings have different energy savings results, on average 30% energy savings were realized between ASHRAE 90.1-2004 and ASHRAE 90.1- 2010 standards. An additional +7% energy savings is anticipated for buildings designed to ASHRAE 90.1- 2013 standards.
It’s both a challenging time and exciting time for engineering innovative products and then applying them in a building design. Previous creative high performance building designs used in the past have been adopted by codes as requirements today. More than ever designing buildings to meet or exceed these code requirements is a holistic team approach.
There are several basic considerations and steps when designing buildings to optimize energy savings and comply with these mandatory requirements.
Reducing heat gains and losses through the building envelope (walls, windows, and roofs) is easily accomplished by increasing the insulating values of materials used, the reflectivity and thermal mass of those materials as well as the solar orientation of the building.
Reducing internal heat gains also significantly affects energy savings. Energy efficient lighting and products not only reduces the energy these devices consume but it also reduces the air conditioning loads. Lighting power density limits alone have been reduced from 2.0 watts per square foot or more to .9 watts per square foot or less depending on the application. LED lighting systems are quickly becoming standard design practice. The most significant changes are the requirements for lighting controls utilizing daylight harvesting/automatic dimming, occupancy and vacancy sensors, etc. to be able to automatically turn lights on or off. Additional controls are also being implemented to de-energize receptacles during unoccupied/night times.
The reduction of heat gains and losses through the building envelope coupled with the reduction of heat producing equipment and lights allows the heating and cooling equipment capacities to be reduced thus also conserving energy.
While significant changes have occurred through the type and control of lighting systems, the current code requirements also significantly changes how Heating, Ventilating and Air Conditioning (HVAC) systems are designed since these systems are the largest consumers of energy in a building. There are two primary components which affect energy usage, the generation of the heating and cooling medium and the transportation of the medium to where needed in the building. While manufacturers are responsible for developing energy efficient equipment that complies with the minimum efficiencies required by code to generate the heating or cooling medium it’s still the responsibility of the design engineer to apply this equipment in a system to maximize its performance at peak and part load conditions. The code has also become more stringent in limiting the energy consumed by building systems to distribute the energy, by fans and pumps, through the building. Pipe and duct sizes are larger today to meet reduced frictional pressure losses. Distribution equipment needs to be strategically located to reduce the most critical pressure drop path so as to minimize pump and fan motor brake horsepower. Together the design of the water and air distribution systems have to meet these power limitations.
Another way the code has significantly changed over the years and is a result of changes in technology is the use of variable speed drives (VSD) and electronically commutated motors (ECM) to vary the speed of motors. For example, a 10 HP fan operating at 50% capacity uses 1.25 HP of energy. ECM’s have burst on the scene replacing inefficient shaded pole and permanent split capacitor fractional horsepower motors typically used for fan coil units, heat pumps, exhaust fans, in-line circulators, etc. and are becoming available in larger horsepower motors. ECM motors can also vary in speed based on load (temperature sensor signal).
The mandatory use of heat recovery is becoming more stringent in each update of the code as well and we see that trend continuing in the future. Air side heat recovery uses building relief or exhaust air stream to pass through a heat recovery device to reclaim and reuse energy to precondition outside air for code required ventilation before wasting it to atmosphere. While air side heat recovery has been predominate the past decade, new equipment and system designs are incorporating water side heat recovery. Water side heat recovery can capture and reuse waste heat from air conditioning equipment to make useful heat for heating the building when both mechanical cooling and heating are needed. All in all, the codes are directing the system design to reuse every possible BTU of energy before wasting it to the atmosphere or ground heat sink.
As with lighting systems much is dependent on automatic controls to maximize energy savings for the equipment applied to an engineered system that is unique to each building. Carbon dioxide sensors are being required in smaller assembly spaces to control how much outdoor air is being introduced into the building to meet ventilation requirements. Robust weather sensors to determine ambient air conditions, devices controlling speeds of large motors and meters used to measure flow all play an important role to sequence equipment in the operation of the system while meeting all code setpoints and reset requirements.
Most importantly however is selection of system type, its associated equipment, and the system design for a building. There is no silver bullet solution as each building is unique to itself. Geothermal systems are a popular choice since for every one BTU of energy consumed, on average three BTU’s of useful energy are free. Central heating and cooling systems using boilers, chillers and air handling equipment have long been the system of choice. A relatively new system to the US market, a variable refrigerant volume (VRV) or variable refrigerant flow (VRF) offers a new energy efficient choice. This system is refrigerant based, uses a variable speed compressor to transport energy and has the fewest amount of heat exchangers which increases the efficiency of a system.
The use of energy modeling at the earliest concept stages of design and through life cycle cost analysis can help in determining the type of system.
Industry standard equipment, building design, conventional design and operating parameters and how systems are controlled are in the state of change. Today’s building design engineers need to be innovative and creative in the development of systems while using the laws of engineering to maximize the coefficient of performance (COP) for each building.
Alban Engineering is a Mechanical/ Electrical / Plumbing Consulting Engineering firm specializing in LEED Certified and High Performance design for Public and Educational Facilities. Jeff Alban has won several Regional ASHRAE Technology Awards for innovative designs which incorporate ASHRAE standards.