Selected Laboratory Energy Efficiency Measures

Transcription

1 Selected Laboratory Energy Efficiency Measures These are some of the most effective energy efficiency measures for laboratories 1. Reduce (optimize) air changes per hour in lab space 2. Design to the proper load (right-sizing) 3. Decouple the cooling and ventilation systems 4. Minimize or Eliminate Reheat 5. Install a low pressure drop air delivery system 6. Use variable air volume (VAV) fume hoods 7. Implement Unoccupied Air Flow Setback in Lab 8. Implement supply fan static pressure setpoint reset (for VAV systems) Measure Description Baseline/Standard Design Practice Estimated Cost Effectiveness 1. Reduce (optimize) air changes per hour in lab space. The only code guidance on lab air change rates is for Class H6 areas and a section regarding flammable liquids in a Class B space, which requires 6 air changes per hour (ACH) taken at floor level. In the absence of code guidance, standard practice is to use standards, rules-of-thumb, and legacy designs to set the air change rate. If fume hoods & exhaust arms are operating safely, the lab shouldn t need large amount of room dilution air (high ACH). A reasonable ACH should be maintained to control spill events. Current lab standards recommend a minimum of 4-6 ACH. 10 ACH for general lab space 12.5 ACH for general vivarium spaces Investing a little extra design and coordination time upfront can yield significant energy and energy cost savings. Possible significant first cost savings through downsizing of mechanical systems.

2 2. Design to the proper load (rightsizing). Typical Open Lab Load Design is approximately 15 W/sf. Typical Open Lab Measured Load 2-5 W/sf. Potential Best Practice Sizing 7-10 W/sf Maintains >50% + safety factor Impact of Right Sizing to Load Smaller cooling system Smaller Air Handlers Smaller Ducts Smaller Exhaust Fans Smaller Generator Varies by facility and application. Needs to be evaluated on a case-by-case basis. May not be incentable under PG&E programs, but should be still be an integral part of any HVAC design. MEDIUM to Often designers will add safety factors upon pre-existing safety factors to the point where systems are extremely oversized. Conducting a proper load analysis, and designing systems to the proper load can save significant first cost and operating cost without adding appreciable engineering time. 3. Decouple the cooling and ventilation systems Use chilled beams, fan coils, etc, for cooling instead of the ventilation air. Since the air is 100%OSA, it is very energy-intensive to cool (or heat) all of that air when cooling (or heating) can be done in the space with much smaller air volumes. Baseline/standard practice is to combine the ventilation and cooling systems. Implementing this best practice saves significant energy through not having to condition large volumes of outside air that is exhausted after one pass through the lab spaces.

3 4. Minimize or Eliminate Reheat Instead of supplying cold air to all spaces, only to be reheated at the zone level to the proper supply air temperature setpoint, minimize this reheat through thoughtful design by either a) installing two or more different air systems supplying air at high and low temperatures, and/or b) reset the supply air temperature upward as much as possible when not at peak cooling load in order to minimize the necessary reheat for lightly loaded spaces. Baseline/standard design practice is to supply cold (~55F) air to all lab spaces, which is then reheated at the zone level to the required supply air temperature setpoint for all but the most loaded spaces. MEDIUM to Depends highly upon the load profiles in the individual lab spaces, but in general the minimization or elimination of reheat will save significant energy. May add appreciable first cost in more complex design, controls, and serving the lab with multiple systems instead of one system.

4 5. Install a low pressure drop air delivery system Can be accomplished through many different design strategies, including low-face-velocity air handling units, low pressure drop ductwork, elimination of sound attenuators, low pressure drop air terminals (i.e. VAV boxes) and zone heating and cooling coils, and low pressure drop heat recovery equipment. Baseline component pressure drops: AHU (incl. filters, coils, fan) = 2.5 w.g. Air handler silencer and/or duct silencers = 1.0 w.g. Supply ducts and VAV boxes (not incl. zone reheat coils) = 3.0 w.g. Zone reheat coils = 0.5 w.g. each Total exhaust system pressure drop = 1.7 w.g. (We use 0.7 for the exhaust stack plus 1.0 for the exhaust duct, up to and including a vertical run of 3 floors. We add 0.5 for every additional floor beyond a vertical run of 3 floors.) Air Handler face velocity: AHU face velocity = 500 fpm As long as mechanical designers are spending the time to design an air system, making low pressure drop design a priority does not require any significant extra engineering time. May be increased coordination time between mechanical and other disciplines due to larger AHUs, larger ducts, etc.

5 6. Use variable air volume (VAV) fume hoods. Labs typically require 100% outside air, so reducing the volume of air is usually a prominent target for energy efficiency improvements. Variable air volume (VAV) fume hoods can help in this regard. They are a mature technology and becoming more common. Baseline/standard practice is to use constant air volume (CAV) fume hoods. LOW to Implementation of VAV fume exhaust is not cost effective in all circumstances. In cases where the space general exhaust (not fume hoods) dominates, the energy savings can be small or zero. As the user closes the sash when the hood is not in use, less air is needed for safe containment, which can lead to significant fan power savings. This requires a more complex ventilation system, to dynamically match exhaust requirements. VAV hood savings are small or zero if the space general exhaust dominates, either due to a large ventilation rate or a small number of fume hoods. Proper use of hoods is essential to realize savings; user education, signage, and training of janitorial staff to close hoods when not in use are essential. In addition to fan energy savings, the reduction in air volume decreases the loads placed on the heating and cooling plants. It may be possible to downsize the plants. If so, the first cost savings will help offset the increased cost of the VAV hood exhaust system. But in every case where the fume exhaust dominates (over general exhaust, ventilation, and cooling), this measure can be very costeffective.

6 7. Implement Unoccupied Air Flow Setback in Lab When the lab is unoccupied, the ACH can be reduced since spill events are not likely and if they do occur will not expose occupants. Current lab standards recommend a minimum of 4-6 ACH. We suggest 6 ACH while occupied, 4 or less when unoccupied. A time clock can be used, or an interlock with the lights if the environment contains relatively hazardous substances. This measure saves fan energy and the energy required to temper outside air (mostly heating, but also some cooling). Baseline/standard practice is to maintain design air flow during unoccupied hours. Additional engineering time for an unoccupied air flow turndown is minimal, as is the additional equipment needed (occupancy sensors or time clocks, and overrides). The fan energy savings is significant, making this measure very cost effective in nearly all circumstances.

7 8. Implement supply fan static pressure setpoint reset (for VAV systems). Variable air volume (VAV) air delivery systems use automatic dampers to match the air volume to the demands of each zone. The standard control method is to vary the supply fan speed to maintain a constant static pressure in the supply duct. The static pressure setpoint is set high enough to deliver the maximum design air flow when all the dampers are wide open. At part load conditions (most of the time), the dampers close down against this pressure. A lower static pressure would serve to deliver the needed air, reduce noise, and save energy. An analogy: The baseline control scheme is akin to driving your car by flooring the gas pedal and modulating the brake to control your speed. Baseline/standard practice is to maintain a constant supply fan duct static pressure setpoint at all times. MEDIUM to Cost effectiveness depends on the diversity of loading in the zones served by the HVAC system, and the individual load profiles of each zone, but in most multi-zone VAV applications a static pressure reset is very cost effective. Significant fan energy savings can result from the reduction of duct static pressure, and minimal extra engineering, installation, and commissioning time is required. A direct digital control (DDC) system can continuously poll the dampers to determine their positions. If all the dampers are less than 90% open, the static pressure setpoint can be reduced until at least one damper is 90% open. (Not going to 100% retains the ability to smoothly control the dampers.) (Courtesy Rumsey Engineers 3/08)