Section VI- Strategies a.) Summary: It is important for new construction designers to consider the heating, ventilation, and air conditioning needs within a building. There are many different systems, and each tends to be unique to its building. It is very important to design the system based on the individual building to make sure the equipment is not oversized. Adding quality to the envelope and minimizing loads can also reduce the final costs. The following strategies are recommended by SEDAC to increase efficiency of systems: Demand Control Ventilation (DCV) High efficiency equipment o Condensing boilers o Variable frequency drives o Economizers o Air source heat pumps o Chilled beams o Variable refrigerant flow (VRF) b.) Technical Information: Demand Controlled Ventilation: Ventilation is the process of bringing outside air into a building to provide building occupants with fresh air. Depending on weather conditions, ventilation air must usually be either heated, cooled, and/or be dehumidified. Because of this, ventilation air represents a significant portion of energy consumption. Maximum ventilation rates, or the amount of fresh air in cubic feet per minute (CFM) that an air handler system brings into a building is based on the maximum number of people that can occupy the space being served by an air handler. It is not unusual for an air handler to operate at the maximum ventilation rate continuously, even if the space is only partially occupied. This method of operation results in over-ventilation and wasted energy. Since buildings are rarely at maximum occupancy, significant energy savings can be achieved by reducing the amount of outside air being introduced into the building and then conditioned without compromising air quality. Demand controlled ventilation (DCV) is a method that controls ventilation rates based on the concentration of carbon dioxide (CO2) of interior air while maintaining proper indoor air quality. 1 P a g e
Since buildings are rarely at maximum occupancy, significant energy savings can be achieved by reducing the amount of outside air being introduced into the building and then conditioned without compromising air quality. Demand controlled ventilation (DCV) is a method that controls ventilation rates based on the concentration of carbon dioxide (CO2) of interior air while maintaining proper indoor air quality. CO2 sensors placed in the return air duct system monitor the concentration of CO2, which increases or decreases based on the number of people in the building. The sensors signal the outdoor air dampers when to adjust the amount of air to be introduced into the air-handler so that fresh air requirements are met. Many new systems already use this type of ventilation control and it is possible to retrofit older systems with comparable controls. Alternatively, if a building has equipment scheduling capabilities and the capability to modulate outdoor air dampers, the air intake rates can be lowered during stretches of low occupancy. Condensing boilers: Non-condensing hot water boilers are built and operated to avoid condensation from occurring in the heat exchanger. To do so, temperatures within the heat exchanger need to be kept above approximately 140 o F. This requirement causes flue gasses to be quite hot which are then vented to the exterior. Jacket losses from these boilers can also be considerable since minimum temperatures need to be maintained. Conversely, condensing boilers are built from materials that can withstand the corrosive effects of condensation, capture the heat that non-condensing boilers exhaust out the flue, and have much lower jacket losses since they can operate at temperatures well below a non-condensing boiler, and capture heat off of the heat exchanger. 2 P a g e
Because boilers are typically sized to satisfy heating loads during the coldest anticipated weather, which occurs infrequently, they usually operate at part-load. Therefore, condensing technology can substantially increase the overall operating efficiency of the hot water heating system. Current condensing boiler technology with high turn down ratio can achieve efficiencies between 85-97%, with peak efficiency at low-fire rates and lowreturn water temperature. With proper system design and operation, this characteristic allows condensing boiler technology to be particularly efficient at partial loads as opposed to non-condensing boilers which operate below their rated maximum efficiency under part-load conditions. 3 P a g e
Variable Frequency Drives: Standard operating procedure for most electric motors that drive pumps and fans is for them to be either on, and run at full-speed, or off. Motors frequently do not need to run at full-speed and allowing them to run at a slower speed can save energy, money, and increase the life of the motor. Adding a variable frequency drive (VFD) to a motor allows the speed of the motor to vary to meet the load at any moment. VFDs control the speed of an AC motor by varying the motor s supplied voltage and frequency of power. VFDs are effective in applications with pumps or fans that frequently experience a variable load. Good indicators that a VFD addition would be effective are situations which require the motor to frequently cycle on/off or to operate constantly using valves or dampers to regulate flow. VFDs are commonly applied to motors on air-handlers, cooling towers, large exhaust motors, and chilled water or hot water (hydronic) pump motors. For example, for the fan motor on an air-handler serving a variable air-volume (VAV) system, static pressure in the duct system can be measured and as VAV boxes reduce airflow, static pressure increases in the duct system can trigger the VFD to reduce fan speed. VFDs must be programmed for each installation to avoid potential resonance problems. 4 P a g e
Economizers: Air-side economizers bring fresh outside air into buildings for cooling purposes. The outside air be mixed with exhaust air for desired temperatures. Traditionally, these systems cool buildings whenever outsider air is lower than the temperature of recirculated air. Along with decreasing costs, this method can also improve indoor air quality. Air source heat pumps: Air source heat pumps transfer heat from outside to inside buildings. These systems warm inside of a building while cooling the outside air. The major pieces of this equipment include an outdoor heat exchanger coil, which collect heat from surrounding outside air, and an indoor heat exchanger coil, which transfer heat to hot air ducts. Chilled beams: In a chilled beam system, pipes of cold water are passed through a heat exchanged either integrated into or closely connected to the ceiling. As beams cool the surrounding air, the cooling descends to the floor, causing the warm air to rise. While passive chilled beam systems are controlled only through the convection process, active systems also exist, which include air ducts to push air toward the unit. Variable Refrigerant Flow (VRF): VRF is a good option for buildings with varying loads and different zones. This strategy uses refrigerant as the source for heating and cooling. It includes multiple fan coil units and evaporators throughout the building, which are each connected to one condensing unit. Each unit may be controlled by different users, depending on the varying heating and cooling needs throughout the building. VRF heat recovery technology also adds to the energy saving of this equipment, allowing for heating and cooling only when necessary. 5 P a g e
c.) Case Study: Ground Source Heat Pumps (GSHP) Although it may be expensive, incentives for GSHPs help cover the cost, particularly for the public sector. This particular system had an EER of 13.5 and a COP of 4.5. In this case, the server room cooling tied into the heat pump loop. Their system also includes a dedicated outside variable air volume with the GSHP and heat recovery. DCV was implemented, while economizers and variable frequency drives on the water pumps were installed. User control thermostats with +/-2 F adjustment were also set up to give each occupant a little bit of control over his/her own space. 6 P a g e