LEED Commissioning and Actual Energy Use

Transcription

1 LEED Commissioning and Actual Energy Use John Kokko Enermodal Engineering Synopsis This paper follows two case studies through full LEED Best Practice and Fundamental Commissioning. It uses the original simulations as a baseline for predicted building energy performance. It then shows how design reviews, shop drawing reviews, installation verification, and functional performance testing help guide the design and construction teams through the green building process, avoiding missteps and on to achieving the expected results. Finally it uses measurement and verification results to show how well the actual building performance matches expectations. About the Author John Kokko, P.Eng., is the vice president of Enermodal Engineering. Heading up Enermodal s Commissioning Division, Mr. Kokko has worked in building commissioning for over 20 years and has completed over 80 projects. He has commissioned every type of building from high rise residential to industrial, as well as many LEED buildings such as the Canadian Union of Public Employees head office, Sisters of St. Joseph Residence in London, and University of Calgary s School of Veterinary Medicine. Enermodal Engineering is one of North America s premier consulting firms exclusively committed to green buildings and communities. With a professional staff of 100 in Kitchener, Calgary, Denver, and Toronto, Enermodal is working on over 190 LEED buildings and is responsible for over 45% of all LEED Canada-NC certified buildings. Kokko, John: The Real Performance of Green Buildings 1

2 LEED Commissioning The LEED (Leadership in Energy and Environmental Design) green building rating system was developed by the U.S. Green Building Council (USGBC) to provide a recognized standard to assess the environmental sustainability of buildings. The Canadian Green Building Council (CaGBC) has adapted this credit-based rating system for Canada. Two of the 70 LEED credits (26 are required for certification) involve commissioning: a mandatory prerequisite, Fundamental Commissioning, and an additional credit, Enhanced (or Best Practice) Commissioning. Requiring basic commissioning and encouraging best practices offers a real opportunity for buildings to reach their anticipated energy savings potential. Up to 10 LEED points are available for energy efficiency in the design. These savings are predicted through energy modeling during design rather than actual energy measured performance after occupancy. While simulations can show the potential energy savings, there are still significant design, construction, and operational hurdles that need to be overcome for real buildings to achieve that potential. The LEED system has recognized that commissioning is the critical element required to help the building designers, contractors and operators overcome those hurdles and ensure the building performance actually measures up to the originally predictions. Commissioning for LEED Commissioning has traditionally meant the contractor and/or manufacturer s representative starts up an individual piece of equipment and verifies that it alone functions as expected. Manufacturer s start-up or commissioning sheets usually have simple yes/no questions that verify installation is as per instructions and code. There may be a few questions dealing with connected services such as verification of connected voltage or proper gas pressure is available. However as neither the manufacturer nor the contractor is responsible for the design of the connected services, traditional commissioning does not go beyond the boundaries of the piece of equipment itself. That is, the job of a boiler is to make hot water, not to keep the building warm; the job of an air handler is to move air, not to ventilate and condition spaces; the job of the control system is to start and stop equipment, open and close valves or dampers, reset supply temperatures or pressures, not to minimize energy use while maintaining comfort conditions. This is where LEED, or proper building commissioning as it should be called, comes in. Fundamental commissioning includes some procedural tasks to ensure proper process is followed but also two important field tasks, Pre-Functional Inspections and Functional Performance Testing. These field tests require that equipment is checked for proper installation and operation in and of itself (similar to conventional Cx) but also that systems as a whole deliver the services they were designed to provide. Enhanced Commissioning first takes this one step back into the design phase start requiring peer reviews of the design and shop drawings, and then one step forward requiring commissioning activities continue after building hand-over, up to the end of the first year of occupancy. Kokko, John: The Real Performance of Green Buildings 2

3 Don t Consultants and Contractors already Commission? Why is LEED commissioning necessary? Design consultant and contractor responsibilities for commissioning are commonly misunderstood. Neither is contractually obligated to guarantee building performance. Consultants obligations require meeting building codes but only need to show that they meet average standards of professionalism when it comes to verifying the design meets owner expectations; they do not guarantee performance. Similarly contractors and suppliers need only show they have met the letter of the drawings and specifications and that their equipment in and of itself performs as advertised. Again they do not guarantee performance of the system into which it is installed. The construction process as it has developed in North America also conspires against handing over fully commissioned buildings. Typical projects follow traditional construction practices including acceptance of low-cost bids, undefined performance targets, last minute cost cutting and changes, fast-tracked construction schedules and resistance to adding unnecessary services (like commissioning), all with the expectation of ending up with exemplary buildings. Add to this the demand for increasingly complex and new systems and products (often imported from off-shore) into today s showcase green buildings. Since consultants, contractors, and suppliers are not intrinsically obliged to fully commission as defined by LEED or ASHRAE, only specifically spelling it out in the contract can overcome these shortcomings. Once required by contract, full-service commissioning can then help take performance verification to the next level. What Can Commissioning Accomplish? One of the most valuable commissioning exercises is design review. Required by LEED as an Enhanced Commissioning activity, it can catch basic design flaws before they even make it into the tender documents. Some disturbingly common design shortcomings even still include: 1. Specifying a condensing boiler but designing the radiation for 180 F (82 C) entering water temperatures and 20 F temperature drops. Without return water at about 125 F (52 C) or lower there is no condensing and no savings 2. Variable frequency drives on pumps with loads that still have three-way valves. The drive will not turn down if the flow at the terminal units is stopped 3. Main heating boilers used for indirect domestic water heating requiring large boilers with significant standby losses be run all summer, rather than using dedicated condensing water heaters that provide high efficiency and low standby losses year round 4. Insulation on cold-side exhaust ducting from HRVs/ERVs only insulated within 5 feet (1.5 m) of the wall. Because the HRV/ERV cools the exhaust air stream that duct will pick up and remove heat from the building as it exits 5. Constant circulation of heating water through-out the heating season. For significant portions of winter heat recovery and an energy efficient building envelope can maintain temperatures and no supplemental heat is required. With DDC systems heating valves can be monitored so that heating systems can be off totally and brought on a call for heat only Kokko, John: The Real Performance of Green Buildings 3

4 Design Concepts That Save Money As Well As Energy One common misconception is that commissioning design reviews are all about adding capital costs to the project. While in many cases short payback items that increase construction costs may be recommended, there are often items that actually reduce first cost that can be caught in the design reviews. 1. Equipment sizing based on load calculations using actual building U-values can reduce equipment sizing 2. Use of large temperature drops reduces pipe sizing and pump sizing. While some increase in terminal unit sizing is required there is generally an overall cost reduction. 3. Removal of heat exchangers where they are not actually required. Discussed in the retirement home example below 4. Using passive heat recovery and proper pool air temperature control for humidity control in pools rather than mechanical refrigeration equipment Similarly there are many, many examples of issues that can be identified during shop drawing reviews, installation verification and functional testing that, if not corrected, can have a significant negative impact on final operation of the building. Two LEED Commissioning Case Studies Sisters of St. Joseph Residence, London Building and Energy Use Overview This project is a retirement home and administrative centre for the Sister of St Joseph Diocese in London, Ontario. A four-story, 126,000 ft 2 (12,400 m 2 ) building includes residence rooms, offices, medical and exercise rooms, a chapel and spiritual centre, workshop rooms, and kitchen/dining facilities. Energy saving design began at the concept design phase where an energy simulation commenced with a building design that features high levels of insulation and energy-conserving windows. The mechanical system uses the earth as a heat source in winter and heat sink in summer. A ground loop with 63 bore holes, 328 ft (100 m) deep, supply the building s water-source heat pumps. As the building requires continuous ventilation, significant energy savings result from the use of energy recovery equipment. An ERV is used to recover heat and humidity and return that energy indoors in winter. The same ERV helps reject heat and humidity normally carried in with outdoor air in the summer. Figure 1 shows the main building loop heat pump system. The main source and sink for the system is the bore field. The central air handler (top) provides balanced supply and exhaust air Kokko, John: The Real Performance of Green Buildings 4

5 flows through an ERV wheel with post heating and cooling from a dedicated water-to water heat pump and glycol coil. An air handler is used for kitchen ventilation (bottom) including a dedicated water-to water heat pump but without energy recovery (as the kitchen hood provides dedicated exhaust) is included. All other spaces have water-to air heat pumps off the building loop. There is heat injection from the back-up boilers when there is shortfall from the ground loop. The ground loop was sized to provide sufficient capacity to avoid the need for a cooling tower. Additional mechanical equipment not shown for clarity includes perimeter radiation for common spaces, a parking garage ramp snow melt system, and a therapeutic swimming pool. The mechanical design targeted 52% energy savings and seven LEED points. Figure 1: HVAC system Kokko, John: The Real Performance of Green Buildings 5

6 Commissioning Findings Design Review The first step was to provide design reviews at the 50% and 95% design development stages. Many small items such as excessive pump capacities, undersized ducting, and under-insulated piping and ducting were identified but some of the major items identified included: 1. Removal of a heat exchanger between building loop and ground loop reduced capital cost and increased efficiency. While this meant that the building loop also had 20% ethyl alcohol, the performance reduction in the heat pumps was less than the performance reduction of the ground loop with the heat exchanger 2. The early drawings showed the boiler heat injection located on the upstream side of the ground loop. Moving heat injection to after, rather than before the ground loop connection, eliminated paying to heat the ground 3. The original design showed DHW production as indirect heaters off the building boiler loop. Changing to direct-fired, condensing water heaters provided energy savings from more condensing operation during water heating, reduced stand-by losses in summer with building boilers shut down, and outdoor air reset on the building boilers without the need to increase the temperature on a call for domestic water heating 4. The addition of a heat exchanger between the snowmelt system and the building boiler loop so that glycol could be limited to outside loads where freezing was a concern, but the building loop including perimeter radiation etc. could be operated on water Shop Drawing Review The next step was shop drawing reviews. In this case shop drawings were reviewed simultaneously with the engineers review. Commissioning findings were sent to the consultant for inclusion of pertinent comment in their review returned to the supplier. Findings included: 1. Several re-submittals of heat wheel shop drawings to prepare a proper defrost strategy. Starting with no defrost then using humidity sensors on the exhaust air stream which are unreliable in condensing environments and unstable with time. Finally a pressure drop strategy was provided 2. Performance of heating/cooling glycol coils was originally modeled using water rather than 40% propylene glycol 3. Coils have greater air-side and water-side pressure drops than specified 4. Controls sequences were carbon copy of engineer s general wording rather than converting to specifics that can be programmed Installation Verification and Functional Performance Testing Installation verification and functional testing present a significant opportunity to ensure energy saving features are operating as intended. Kokko, John: The Real Performance of Green Buildings 6

7 Building loop pump control was originally set to a default value of 10 PSI. Working with the balancer it was determined that only 8 PSI was required to provide the design flow through the farthest load and the pressure setting for the VFD pumps was reset down. Motor horsepower is proportional to the pressure difference raised to power of 3/2. This 2 PSI (or 20% reduction in pressure setting) reduced motor power by 30%. And since these pumps operate 8760 hours a year, this is a significant reduction in annual electricity consumption Controls always present the greatest opportunity to ensure energy use issues are addressed and equipment is operating as intended. Some examples of issues identified on this project included the following three items. First, the heat wheel in the common area air handler had a reset controller that the controls contractor programmed as heat wheel speed. The commissioning agent identified that the controller interpreted the signal as a reset on the supply air temperature leaving the wheel. Where the controls contractor was sending a signal to set wheel speed between 0 and 100%, the wheel was resetting the air-off temperature between 63 F (17 C) and 75 F (24 C). Correcting this ensured the proper supply air temperature was reset. Second, the bore field pumps were operating continuously even if the ground was operating in reverse to the required heat transfer direction. A sequence was proposed to the engineer to check that heat was being reclaimed from the ground in heating mode and rejected to the ground in cooling. If not the pumps would be turned off until the temperature in the building loop was higher or lower (as appropriate) than the last recorded temperature returning from the ground. Third, the heat pumps on the two large air handlers were two stage with minimal capacity control (i.e., 0%, 50%, or 100%). Originally the systems were set up to have delivered air temperature control on a PID loop. Unfortunately this caused excessive cycling of the heat pump. By allowing a relatively large dead band (±5.4 F or ±3 C) the heat pump could maintain much longer run times. Since the delivered air was for ventilation as opposed to conditioning, the temperature swing did not negatively affect comfort in the building. To understand the savings this represents in broad terms, the actual use can be compared to the average energy use by similar buildings. In this case average commercial institutional accommodation buildings in Ontario use about 136 kbtu/ft 2 /yr (430 kwh/m 2 /yr). At 66.7 kbtu/ft 2 /yr (210 kwh/ m 2 /yr) this building has about half the energy intensity of the average similar building. While commissioning cannot take credit for all the savings, it is clear that without full service commissioning, all of these savings would not have been realized, and the building would not be operating as intended. Kokko, John: The Real Performance of Green Buildings 7

8 Toronto and Region Conservation Authority, Restoration Services Centre Building and Energy Use Overview The Restoration Services Centre serves as a showcase of sustainable design and a centre for the organization s habitat regeneration and restoration projects. The two story, 20,505 ft 2 (1,095 m 2 ) building comprises office space for 36 staff members and a works garage. The construction is engineered wood framing with brick and wood siding. The Restoration Services Centre concept design achieved a remarkable 66% annual energy savings. Figure 2 shows the innovative HVAC system in a simplified schematic form. Not all components are shown for clarity. Heating and cooling are provided by a ground source heat pump system. The ground loop is a slinky that requires less ground area than conventional ground loops and is less costly than vertical boreholes. The building side is a hydronic system connected to a large storage tank providing thermal storage. Heat and cooling are delivered to the offices through post heating of the ERV air, in-slab radiant heating and cooling, and fan coils in high load areas. The radiant floors provide tempering rather than full cooling. The floor surface temperature is never lowered below 64 F (18 C) to avoid any possibility of condensation. The attached garage is heated by gas-fired radiant tube heaters and has its own HRV for ventilation. Outdoor ventilation air for the offices is first tempered by a concrete earth tube, and two heat recovery ventilators then deliver this 100% outside air to the offices via displacement ventilation (i.e., low level, very low velocity discharge of air into the space). The mechanical design targeted 66% energy savings and 10 LEED points. Kokko, John: The Real Performance of Green Buildings 8

9 Figure 2: HVAC system Installation Verification and Functional Performance Testing The major item that was causing problems with respect to installation issues were as follows. During construction the contractor was asked several times to label the floor loops as per the drawings before the concrete floors were poured. This did not get done. After the systems were started, one office in particular was cold. After two all-day tests where various loops off a single manifold were enabled and disabled, it was identified that a loop in a storage room was crossed with the loop in the office. One heat pump was continually locking out on fault. The heat pump start-up technician blamed the system installation on excessively low water flows but would not measure these as this was not his job. After the flow rates were verified to be to spec the tech then found both a defective TX valve and a low refrigerant charge. The HRV in the garage was required to be enabled and disabled by the BAS system. The specifications called for a premium wall control that provided local control but allowed an external signal to enable and disable the unit so that it could be turned off during unoccupied hours. While the basic control looked similar, it had terminals for a remote push button to turn the unit to high speed. The controls contractor connected to these terminals and had the unit turn Kokko, John: The Real Performance of Green Buildings 9

10 onto high speed whenever the space was unoccupied. Installing the specified control then resolved the issue. During functional testing, correcting controls errors are probably the single most important item in ensuring successful system operation for comfort and energy savings. In this building the controls contractors were reluctant to follow the sequences provided. The controls contractor took it upon himself to provide a more energy-efficient loop by lowering the operating temperature in the hydronic loop during heating. He overlooked the fact that the post heating coil in the HRV and the fan coils required warmer temperatures and were in series rather than parallel with the floors. The switch-over from heating to cooling required a calculation of the moving average on outdoor air temperature to verify that the temperature was going to change far enough and for long enough to justify switching the system over. The routine was originally programmed as an instantaneous temperature change and consequently the system was seen to flip back and forth several times in a single a day, causing the heat pumps to heat and then immediately cool the entire system water volume. Correcting the algorithm resolved the problem. A variable speed pump was used on the fan coil loop but the controls technician had installed a single ended pressure sensor rather than the differential specified. The sensor was set to five feet above the design static head in the piping. The pump was found to be operating at full speed continuously. The system pressure was found to be 3 PSI below the design setpoint keeping the system pressure from ever reaching the setpoint. Installation of a differential pressure sensor resolved the problem. Sister s of St. Joseph Residence Predicted and Actual Energy Use To understand if the building is performing as intended, energy simulation is required. Figure 3 provides simulation results over the course of the project. In this case simulations were done at concept design, during design development and to reflect as-built conditions. As often happens, the initial simulations is an idealized vision of regulated loads (i.e., excluding process loads). As the design develops real building data becomes available and compromises are often made. The simulation with respect to the reference building often ends up with increased energy intensity. In this case energy use rose to approximately 54 kbtu/ft 2 /yr (170 kwh/m 2 /yr) for the LEED submission. Finally process loads such as the kitchen and the pool are added to obtain the asbuilt simulation, in this case approximately 60 kbtu/ft 2 /yr (190 kwh/m 2 /yr), this was still 52% below the reference building energy intensity of 127 kbtu/ft 2 /yr (400 kwh/m 2 /yr). Actual monitored use as provided by M&V data over a year of actual operation can then be compared to the as-built simulation. In this case the actual performance was approximately 67 kbtu/ft 2 /yr (210 kwh/m 2 /yr) or 48% energy savings. Kokko, John: The Real Performance of Green Buildings 10

11 Simulated Actual Aug '04 (SL) Feb '06 (CBIP) Aug '06 (Review) Aug '07 to Feb '08 Figure 3: Energy Simulation Results Toronto Region Conservation Authority, Restoration Services Centre Predicted and Actual Energy Use Figure 4 provides simulation results over the course of this project. Simulations were done at concept design, during design development, and to reflect as-built conditions. As the design developed, the team explored some different designs that would not meet the energy savings targets and had to work through design options until the savings target was reached. With a reference building of 105 kbtu/ft 2 /yr (330 kwh/m 2 /yr) the target of 10 energy points required an energy intensity of under 48 kbtu/ft 2 /yr) (150 kwh/m 2 /yr). When the nominal process loads were added to get the as-built energy consumption energy intensity was expected to be 49 kbtu/ft 2 /yr (155 kwh/m 2 /yr). This was still 65% below the reference building energy intensity. Monitored energy use as provided by M&V data over a year of actual operation can then be compared to the as-built simulation. In this case the actual performance was almost identical to the as-built simulation or 65% energy savings. Kokko, John: The Real Performance of Green Buildings 11

12 Figure 4: Energy Simulation Results Conclusions Obviously commissioning cannot take all the credit for buildings meeting their energy reduction targets. Still it is clear that without a comprehensive full-service commissioning effort as required by LEED to properly complete both fundamental and enhanced commissioning, there are many opportunities for small items to cause excessive energy use. Commissioning has an integral role to play in ensuring that the building operates as intended providing the comfort levels expected, and just as importantly, obtaining the energy savings expected. Kokko, John: The Real Performance of Green Buildings 12