COMPARATIVE LIFE-CYCLE ANALYSIS OF ENERGY-EFFICIENCY MEASURES AT TVA S CHATTANOOGA OFFICE COMPLEX: PHASE II RESULTS & FINAL DESIGN

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1 COMPARATIVE LIFE-CYCLE ANALYSIS OF ENERGY-EFFICIENCY MEASURES AT TVA S CHATTANOOGA OFFICE COMPLEX: PHASE II RESULTS & FINAL DESIGN Umesh Atre Innovative Design Inc 850 W Morgan St Raleigh, NC umesh@innovativedesign.net Michael Nicklas Innovative Design Inc 850 W Morgan St Raleigh, NC nicklas@innovativedesign.net David Zimmerman Tennessee Valley Authority 1101 Market St Chattanooga, TN drzimmerman@tva.gov ABSTRACT This paper presents the second phase of the daylighting & building energy simulation work conducted for Tennessee Valley Authority s 1.3 million sf Chattanooga Office Complex (COC). Once the base daylighting and building energy models were validated for one building (as part of the first phase), energy simulation models were developed and validated for the entire complex, this expanded scope now involving 4 office buildings and data center served by a central chilled water & hot water plant. A 3-step validation had to be performed since the data center was metered separately but still shared the same central plant. equest (DOE-2.2) & Daysim 3.0 (Radiance) software were used for energy modeling & daylighting analysis respectively. The new models for the entire complex were modified to analyze effects of the following energy-efficiency measures: atrium & office daylighting, lighting, plug loads, chilled water & cooling water ΔT, VFDs, reduced outside air, BAS & improved AHU operation, atrium heat recovery & destratification, new chillers, water-source heat pumps, and exhaust air energy recovery systems. The final proposed design is expected to reduce existing building energy consumption by 33%. Daylighting, improved lighting, and plug load optimization represents 58% of the total energy savings. Detailed cost-benefitanalyses suggest a 13-year payback on all measures excluding daylighting, lighting, and plug loads, and a 17- year combined payback. The expected energy savings would help TVA achieve/exceed their rigorous internal energy goals while complying with federal mandates. HVAC and lighting upgrades, combined with other design changes, could qualify this facility for a possible LEED-CI rating. North South Fig. 1: Site Plan of the TVA COC showing buildings A,B,C,D,E,F, and the Computer/Data Center

2 1. BASECASE MODEL VALIDATION The first step involved in the building energy modeling and validation process included getting together relevant information on the following items. Requests were made to the building design team and the building management teams, depending on data classifications. Data requested from the Architects of Record on the COC and/or TVA included the following: Architectural drawings and building assemblies information Mechanical drawings and HVAC zoning Electrical drawings Interior design/furniture layouts Data requested from the Engineering/Building Management teams and/or TVA included the following: Mechanical drawings and HVAC zoning Electrical drawings Occupancy and schedules Lighting schedules Building management schedules Building energy consumption (utility bills) Interior equipment and schedules A 3-step model validation had to be performed for accuracy: was established using the individual building area fractions in comparison to the totals. Though the Monteagle Place (MP) building has an actual (measured) base performance of 250+ Kbtu/sf/yr, it only accounts for 11% of the combined square footage of all the buildings. The actual base performance of the rest of the COC is 58 Kbtu/sf/yr, and the energy performance for the combined model was thus determined to be 79.8 Kbtu/sf/yr, which matches pretty closely with the simulation results for the combined model. Step 1: Validation of the Chattanooga Office Complex model, excluding Monteagle Place (data center) Step 2: Validation of the model for Monteagle Place Step 3: Validation of the combined model for Chattanooga Office Complex, including Monteagle Place Steps 1 and 2 were possible and essential since TVA has been keeping separate utility bill records for Monteagle Place (data center) and the rest of the COC. Fig. 3: Basecase Model Validation Results 2. ENERGY-EFFICIENCY MEASURES 2.1 Summary Of Past Analysis And Current Process Fig. 2: Building Energy Model for the entire TVA COC Since the COC and Monteagle Place models had to be combined, a baseline building energy performance target The past analysis (published in the 2011 ASES Proceedings) for the TVA COC focused on evaluating only one building Lookout Place (LP) to understand the effects of daylighting, lighting, and interior equipment modifications on the existing building s energy performance. Other measures were studied, with the intention of having a more detailed analysis in the future. The current phase of analysis was begun with a model built for the COC (set of 5 buildings), excluding the data center (Monteagle Place). The same first sets of recommendations

3 (daylighting, lighting, and interior equipment) were evaluated for this complex. With the inclusion of the Monteagle Place building to the COC model, it was decided that the COC model (excluding Monteagle Place) not be used to study the further new set of recommendations received from the engineering team, since all of these buildings share the same central plant. Beyond the New Basecase model, a revised model for the entire COC+MP was developed. The following description of runs refers to this revised model. A later portion of the analysis compared the original Lookout Place model, the later COC model, and the final COC+MP model for reference purpose. 2.2 Description Of Runs Baseline Model The baseline model represents the Existing buildings. All as-built architectural, mechanical, and electrical drawings and supporting documentation was used in this run. An image of the baseline building energy model is shown in Fig. 2., and the baseline model validation results for the TVA COC and TVA COC + MP are presented in Fig Daylighting Design This run focused on studying the effects of daylighting on the building energy consumption. Of particular interest was the effect on the interior lighting and cooling energy consumption. Hourly daylighting schedules generated using separate daylighting analysis software (Daysim) were incorporated into the previously validated baseline building energy model. This revised building energy model represents the effect of using the following daylighting design recommendations in existing spaces: Interior fabric baffles in the perimeter spaces, Translucent glazing system in the atrium skylights, High reflectance ceilings, New, reflective surfaces in the light scoops located at every floor level in the atrium, and Interior fabric baffles in the spaces adjoining the atrium A daylighting analysis report was created as a separate document for details on each of the recommended options for the office and atrium spaces. All the other simulation parameters were kept the same as the original model Interior Lighting This run focused on studying the effects of improved, energy-efficient lighting on the building energy consumption. The average ambient lighting intensity used in this analysis is set at 0.8 w/sf, which follows in line with the lighting design that is currently being proposed by the architectural team on this project. The ambient lighting set point for both the daylighting and the interior lighting is set at 35 fc, with supplemental task lighting as required Interior Plug Load Equipment This run included studying the effect of reducing the installed w/sf on the plug load equipment in the COC workstations. Average savings from the Workstation Occupancy Sensors Study and Workstation Occupancy Survey conducted by the TVA s Building Management personnel were used in the office spaces to estimate savings. After discussion with TVA personnel and the architectural and mechanical teams, the three strategies mentioned above (namely, daylighting, interior lighting, and plug load management) were considered to be a definite current or future implementation at the COC. A combined model including these 3 strategies was renamed as the New Basecase, and all future energy measures were then compared against this new model. Note: All the runs beyond this point were based on HVAC recommendations by the PME engineering team (local firm from Chattanooga, TN) working on this project. The following descriptions were summarized from an original HVAC report titled Energy Modeling Packages developed by this engineering team Increase Chilled Water Temperature Difference on Existing Chillers This strategy proposes to increase the chilled water temperature differentials on the existing chillers. Current Lookout Place differential is 14 deg. F., and current Monteagle Place differential is 11 deg. F. This model evaluated the effect of increasing these existing differentials to 16 deg. F. Chillers were modeled be operated at 42 deg. F. chilled water temperature in conjunction with VFDs on the chilled water pumps. Results of this run should be compared to the New Basecase. This is referred to as Run 1 and the Alternate as Alt 1* in Fig.4 and/or Fig.5. Alternate: Results from the run mentioned above show a reduction in pumping energy as expected, but also shows a reduction in cooling energy and cooling tower energy, which are unexpected savings resulting from this measure. One possible reason could be that with reduced pumping, the heat generated by the pump motor is reduced and thus less of it gets transferred into the chilled water loop. The chillers see less heat as compared to the basecase, resulting in cooling savings and lower heat rejection. Though this could be a possible reason, the magnitude of cooling savings is not proportionate to the reduced heat generated by the pumps.

4 Fig. 4: Integrated Energy Saving Sets for the COC+MP, COC, and the original LP (Lookout Place) models Fig. 5: Building Energy Performance of Individual Runs (beyond New Basecase) for the COC+MP model Hence an Alternate was presented assuming no cooling or tower savings are achieved in this run. This was intended to provide a best and worst case scenario and determine a range on the savings. Note: Alternates were also presented for all the future runs that feature either a change in the chilled water temperature differential and/or the cooling tower water temperature differential.

5 2.2.6 Increase Cooling Tower Water Temperature Differences on Existing Cooling Towers This strategy proposes to increase the cooling tower water differentials on the existing cooling towers. Current cooling tower differentials are 10 deg. F. This model evaluated the effect of increasing these existing differentials to 14 deg. F. Cooling Tower pumps were modeled with VFDs. Results of this run should be compared to the new basecase. This is referred to as Run 2 and the Alternate as Alt 2* in Fig.4 and/or Fig Cooling Tower Fans VFD Controls This strategy proposes to install variable frequency drives on the cooling tower fan motors. The basecase model was modified to include VFD controls on the pumps. Results of this run should be compared to the new basecase. This is referred to as Run 3 in Fig.4 and/or Fig.5. Note: A combined simulation of runs 2 and 3 was run to see the effect of both these applications together. This is referred to as Run 2&3 and the Alternate as Alt 2&3* in Fig.4 and/or Fig Reduction In Outside Air Quantity This strategy proposes to reduce outside air quantity by improved particulate filtration and cleaning of air stream gas contamination using Bi-Polar Ionization method. The outside air target reduction is from 15 cfm per person to 5 cfm per person. Air handlers would also be upfitted with MERV 6 (30%) prefilters followed by MERV 13 (85%) final filters to arrest particulates. Bi-Polar Ionization hardware would be installed between the final filters and coil bank. This model evaluated the energy savings resulting from the reduced outside air conditioning. Data received from the engineering team suggested that no additional static would need to be added due to these modifications. This is referred to as Run 4 in Fig.4 and/or Fig.5. reduction in fan horsepower requirements associated with all core area air handlers operating under a full DDC controlled duct pressure optimization in a True VAV mode. This is referred to as Run 5 in Fig.4 and/or Fig Atrium Heat Recovery and Destratification This strategy proposes evaluation of the heat recovery opportunities in the atriums. Heat trapped below the skylights can be captured and used during the heating season (October-March). Large-blade fans would be installed in the atrium that could induce enough ventilation to drive the stratified air from the upper levels of the atrium to occupied zones. This modeling package could not be evaluated using the building energy analysis software and savings were calculated using a custom excel spreadsheet. Hourly temperature reports were generated to estimate the amount of usable heat. This is referred to as Run 6 in Fig.4 and/or Fig.5. Note: These fans could also be operated during the summer seasons to allow for a small increase (2-4 deg. F) in thermostat cooling set-points thus taking advantage of the ventilation leading to cooling savings. The savings are currently limited to heat recovery in the heating season only. Comparison between the existing condition and the proposed daylighting design in the atrium spaces (one of the large blade fans is seen in the proposed image) is shown in Fig. 6. The current primary issue of direct beam radiation is mitigated through the use of translucent skylight glazing. Note: This particular strategy is still under consideration due to influence of LEED modeling guidelines BAS/Improved Air Handler Operation This combination of strategies proposes to evaluate energy savings associated with a full conversion to a micro-processor based Variable Air Volume (VAV) HVAC system. The savings would also be extended to all of the system hydronic equipment components. Currently pneumatic thermostats control ceiling diffuser vanes in the core spaces. Air valves located at branch take-offs of each duct adjust static pressure above the diffusers, but there is no direct communication/signaling between all the branch ducts. This model evaluates Fig. 6: Comparing Existing and Proposed Daylighting in the Atrium space at COC Integrated Set 1-6 Runs of combination strategies allowed the design team to understand and compare the effects of individual

6 strategies versus overall effects. The following 2 sets were considered: 7A: Integrated Set of 1-6 runs with 5 and without run 4 (reduced OA), and 7B: Integrated Set of 1-6 runs with 5 and with run 4 (reduced OA). These are referred to as Run 7A and 7B, and the Alternates as Alt 7A* and Alt7B* in Fig.4. The reason for the two different sets was due to the fact that the reduced outside air strategy was still under consideration, as mentioned earlier New Chillers This strategy proposes evaluating replacement of 2 of the existing Lookout Place chillers with cooling-only type high-efficiency machines. All 3 chillers in Monteagle Place were modeled as existing without any modifications. Data obtained for the Trane CenTraVac machines was used in this analysis. This modeling run was further improved upon in the next package with the integration of a water source heat pump. This is referred to as Run 8 in Fig.4 and/or Fig Water Source Heat Pump This strategy proposes evaluating integration of a high water temperature water source heat pump in the Monteagle/Lookout Place chiller mix to reduce heat recovery cost. A 350 ton heat pump has been evaluated based upon the hot water and efficiency parameters received from the engineering team. This run was combined with the earlier run (run 8), and the results for run 8 include savings from this recommendation. strategies versus overall effects. The following set was considered: Integrated Set of 1-10 runs with 7B as the final option selected from the series 7 runs. These are referred to as Run 11D and the Alternate as Alt 11D* in Fig.4 and/or Fig.5 The energy savings from these final simulation models should give an idea of the combined potential of all the strategies listed above. 3. CONCLUSIONS A holistic approach to the problem is an essential step towards understanding the complex relationships between architectural, mechanical, and other design disciplines that play a role in building design. The paybacks of each evaluated measure, if viewed independently, suggests a much different answer than a combination of measures, either in combinations of two or more. The final proposed design is expected to reduce existing building energy consumption by 33%. Daylighting, improved lighting, and plug load optimization represents 58% of the total energy savings. Detailed cost-benefit-analyses suggest a 13-year payback on all measures excluding daylighting, lighting, and plug loads, and a 17-year combined payback Building Exhaust Energy Recovery This strategy proposes to evaluate the effect of using a water-to-air run-around cycle for recovering energy from the building exhaust stream. The energy recovered would be used to pre-cool outside air during the summer seasons and pre-heat during the winter seasons. This model should have been an add-on to #4 Reduction in Outside Air Quantity, but as that strategy is currently on hold, the current model should be compared against the new basecase. This is referred to as Run 10 in Fig.4 and/or Fig Integrated Set 1-10 Runs of combination strategies allowed the design team to understand and compare the effects of individual