C-BOA Tool. Comparison of Peak Demand Savings Estimation Methods. February 7, of 14

Transcription

1 C-BOA Tool Comparison of Peak Demand Savings Estimation Methods February 7, of 14

2 Table of Contents Summary... 3 Recommendation... 3 DEER Periods... 4 Comparison of Estimated Demand Savings... 4 Appendix A - Detailed Results... 8 Air Handler ECMs... 8 Chiller Plant ECMs... 9 Appendix B Sample Building Characteristics Baseline Inputs ECM Inputs of 14

3 Summary This report summarizes how the new C-BOA Tool (Custom Building Optimization Analysis Tool) calculates annual peak demand savings, and shows how those savings compare to savings estimated for the DEER peak demand period. The result will help California utilities determine how the C-BOA Tool is used to report estimated peak demand savings as part of utility retrocommissioning programs in California. The C-BOA Tool estimates annual peak demand savings as the calculated demand savings at the highest outside air temperature (OAT) from TMY weather data 1 for a given climate zone and schedule. This matches the methodology currently used by commissioning providers in many of California s utility retrocommissioning programs. When providers use the bin temperature method to calculate the estimated demand savings related to implementing ECMs, they select the demand savings at the highest bin temperature for program reporting of peak demand. This approach is slightly different from the DEER 28 definition of peak demand, but during development of C-BOA it was judged to be a reasonable approximation. The DEER 28 peak demand periods occur at high OATs. To quantitatively assess the reasonableness of the C-BOA Tool s approximation of peak demand, we have compared annual peak demand savings calculated by two methods: 1) Using the C-BOA Tool but limiting the timeframe of the analysis to only the DEER 28 peak demand periods, and 2) Using the C- BOA Tool s default of peak outside air temperatures selected from the full TMY. The two methods were applied to a sample building with each of the nine energy conservation measures (ECMs) included in the tool. The analysis found that the DEER period demand savings are reasonably close to the peak temperature demand savings, only slightly greater. This variation is probably due to the fact that the OATs in the DEER periods are lower than the peak OATs, and the demand savings for these ECMs decreases with increasing OAT. Recommendation Based on the results of this analysis, which are detailed in the body of this report, we recommend that the estimated annual demand savings as calculated and reported by the C-BOA Tool, which is based on peak OATs, be allowed for use in reporting estimated ECM peak demand savings as part of utility retrocommissioning programs in California, except for climate zone 1 (see discussion in following paragraph regarding climate zone 1). The reported peak demand savings may be slightly conservative (low), since the analysis presented in this report found that the peak temperature demand savings values are lower than the DEER period demand savings. At this time, the C-BOA Tool is complete and ready for release by industry practitioners. Since this analysis shows that the estimated demand savings using the two methods are reasonably close, we recommend allowing use of the tool for calculating estimated peak demand savings. Perhaps a future version of the tool could directly calculate the estimated DEER demand period savings, based on the 8,76 weather data. However, this would not necessary be an improvement, as the DEER peak demand period itself is only an approximation of the system peak load that is approved for planning purposes. The analysis showed a large variation in the DEER demand savings and the peak temperature demand savings for climate zone 1, likely due to the significant temperature difference between the DEER period OATs and the peak OAT for climate zone 1 included in the TMY3 data set. We recommend that providers use an alternate method for calculating the estimated demand savings in climate zone 1. We don t expect this to have a significant impact on the current retrocommissioning programs, though, as climate zone 1, which is the coastal area north of the Bay Area, represents an area with relatively few medium to large commercial buildings. 1 Typical meteorological year weather data available from NREL. 3 of 14

4 DEER Periods For reporting peak demand savings, utility energy efficiency programs in California use the peak demand periods defined in DEER In DEER 28, these periods are defined as follows: The DEER demand period is from 2p.m. to 5p.m. on the days listed [in Table 1] for each climate zone. Demand values are calculated as the average hourly energy reduction during this nine-hour period. This is different from the DEER 25 definition of the peak demand period, which is the hottest 3-day heat wave that does not include weekends and holidays for all building types except educational buildings. Table 1. Peak demand period used for DEER 28 (changes from 25 analysis are highlighted) 2 Comparison of Estimated Demand Savings The C-BOA Tool currently reports the peak demand savings for each ECM as the estimated demand savings at the highest temperature seen in the hourly weather data for that particular climate zone and operating schedule. To compare the estimated DEER peak demand savings with the estimated peak temperature demand savings, a sample building was input into the tool, with sample ECMs. See the baseline building and ECM inputs in Appendix B Sample Building Characteristics. Each ECM in the C-BOA Tool was run for two scenarios for each climate zone: DEER period as the schedule, for calculating the DEER period demand savings. The DEER periods are shown in Table 1 above. The demand savings was calculated by the tool at each of the nine hours in the DEER period, and then those nine values were manually averaged to obtain the DEER period peak demand savings. Monday - Friday 6 am 6 pm as a typical commercial building operating schedule, for calculating the peak temperature demand savings. The peak demand savings is the demand savings at the highest OAT. The results are shown in Figure 1. 2 From 28 DEER Update - Summary of Measure Energy Analysis Revisions, Version for Planning/Reporting. December of 14

5 Figure 1. Demand savings comparison by ECM Overall, the peak demand savings for these ECMs are low, since these ECMs have a greater impact on the usage of the system than the peak demand, which is typical for HVAC operational ECMs. For example, the CWST Reset measure for the sample building shows the greatest demand savings, at approximately 2 kw. However, this is only 3% of the peak HVAC system demand of ~63 kw. In 83% of the test instances, the estimated DEER peak demand savings is slightly more than the estimated peak temperature demand savings. For the instances where the peak temperature demand savings was greater than the DEER peak demand savings, most of these were in the SAT Reset ECM, which has only a slight estimated demand impact. The DEER savings are greater than the peak temperature savings since the DEER OATs are lower than the peak OATs, and for all ECMs except SAT Reset there s greater demand savings at part load / mild temp conditions, not peak load / peak temp conditions. See Table 2 below for a comparison of OATs seen in the DEER demand periods and the peak OATs in the TMY3 data. Figure 2 compares the estimated savings values by climate zone. Positive values indicate that the DEER period demand savings are greater than the peak temperature demand savings. 5 of 14

6 Figure 2. Demand savings comparison by climate zone As shown in Figure 2, the DEER savings are only slightly greater than the peak temperature savings except for climate zone 1. Overall, the demand savings is low since these ECMs have a greater impact on demand at milder climate conditions. The peak demand of the HVAC system as modeled by the C- BOA Tool is 635 kw. Climate zone 1 shows a large difference between the estimated DEER demand savings and the estimated peak temperature demand savings, which is why we are recommending that the tool not be used for estimating the peak demand savings for projects in climate zone 1. This large difference is likely due to the large OAT difference between the 8,76 peak OAT and the OATs during the DEER period see Table 2Error! Reference source not found.. For most commercial buildings in California, electric demand increases with increasing OAT. Therefore, OAT can be used as an indicator of electric demand the higher the OAT, the higher the electric demand. Table 2 compares the OATs in the DEER demand periods with the peak OAT for each climate zone. The right hand column shows the difference between the two. In all cases, the DEER OATs are less than the peak OAT. For some climate zones, such as climate zone 1, the difference is quite large. DEER 28 revised this definition, and as Table 2 shows, the DEER 28 periods do not necessarily include the hottest time of the year, based on TMY3 data. 6 of 14

7 CZ Zip Code Representative city Peak Temp, F From DEER Start Date of 3-day period Max Temp, F From 8,76 data Date of max temp Average temp during ninehour DEER period, F Difference between Max Temp and Average DEER Temp, F CZ Arcata 8 Sep 3 8 Oct 1, 1 pm CZ Santa Rosa 99 Jul July 22, 2 pm 96 3 CZ Oakland 89 Jul Sept 28, 2 pm 81 1 CZ4 944 Sunnyvale 97 Jul July 18, 2 pm 89 8 CZ Santa Maria 93 Sep 3 93 Sept 4, 1 pm 83 1 CZ Los Angeles 85 Jul 9 89 Sept 24, 11 am 79 1 CZ San Diego 92 Sep 9 92 Sept 11, 2 pm CZ El Toro 98 Sep Sept 24, 1 pm 92 6 CZ9 921 Pasadena 11 Aug 6 12 Sept 24, 2 pm 93 9 CZ Riverside 14 Jul 8 14 July 1, 2 pm 11 3 CZ Red Bluff 14 Jul July 14, 2 pm 99 6 CZ Sacramento 13 Aug 5 13 August 6, 3pm 11 2 CZ Fresno 16 Aug Aaugust 15, 4 pm 14 2 CZ China Lake 16 Jul 9 16 July 1, 2 pm 14 2 CZ El Centro 114 Jul July 9, 3 pm 11 5 CZ Mount Shasta 96 Aug 6 96 August 6, 4 pm 93 3 Table 2. Comparison of DEER period temperatures and peak temperatures 7 of 14

8 Appendix A - Detailed Results The results of the individual runs are presented in this section. Where bars are not shown in the charts for certain scenarios, this means the estimated peak demand savings for that scenario is kw. Air Handler ECMs Peak Demand Savings, kw DEER Economizer Peak Temp Economizer Peak Demand Savings, kw DEER SAT Reset Peak Temp SAT Reset Peak Demand Savings, kw DEER DSP Reset Peak Temp DSP Reset 8 of 14

9 Peak Demand Savings, kw DEER SF VFD Peak Temp SF VFD Peak Demand Savings, kw DEER RF VFD Peak Temp RF VFD Chiller Plant ECMs Peak Demand Savings, kw DEER CHW pump VFD Peak Temp CHW pump VFD 9 of 14

10 Peak Demand Savings, kw DEER CHWST Reset Peak Temp CHWST Reset Peak Demand Savings, kw DEER CWST Reset Peak Temp CWST Reset Peak Demand Savings, kw DEER CT Fan VFD Peak Temp CT Fan VFD 1 of 14

11 Appendix B Sample Building Characteristics Baseline Inputs General Component Value Units Source Area, sf 2, sf Input AHU - Scratch pad for inputs Component Value Units Source SF design airflow 1 cfm/sf Estimate SF design airflow 2, cfm Input, calculated SF TSP 4.5 in H2O Input SF motor eff 95% Input SF motor load 85% Input SF design eff 8% Estimate SF design BHP 177. HP Calculated SF nameplate HP 2 HP Input, based on BHP RF design airflow 2, cfm Input RF TSP 1 in H2O Estimate RF design eff 6% Estimate RF design BHP 52.4 HP Calculated RF nameplate HP 75 HP Input, based on BHP RF motor eff 95% Input RF motor load 85% Input Cooling plant - Scratch pad for inputs Component Value Units Source CHW pump design flow 1,5 gpm Input CHW pump design head 8 ft Input CHW pump design eff 7% Input CHW pump BHP 43.3 HP Calculated CHW pump nameplate 5 HP Input CHW pump motor eff 95% Input CW pump design flow 1,7 gpm Input CW pump design head 4 ft Input CW pump design eff 7% Input CW pump BHP 24.5 HP Calculated CW pump nameplate 3 HP Input CT fan kw input 2 kw Input, based on estimate of.35 kw/ton. 11 of 14

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13 Climate Zone 1 s inputs are slightly different, due to the milder climate (max 8F temperature). For Climate Zone 1: 7F system no-reheat point Change OATs in SA flow regression to 1/33/57/8 Change OATS in SAT and RAT regressions to 1/38/52/8 13 of 14

14 ECM Inputs ECM Economizer SAT Reset DSP Reset Test Change OAF from 2% to 1% max OAF, 2% min OAF. Change from 55 to 6 at OAT, 55 at 1 OAT, linear in between. Change baseline SF control from IGV to VFD (8% efficient). Change DSPSP from constant 1.5" to reset between.5" (3% flow) and 1" (9% flow). SF VFD RF VFD CHW pump VFD CHWST reset Change SF control from IGVs to VFD. 8% VFD efficiency. Change RF control from DD to VFD. 8% VFD efficiency. Add VFD to pump. 8% efficiency. 2' setpoint. Reset CHWST from 44F (9 OAT) to 54F (33 OAT). CZ1: Reset CHWST from 44F (8 OAT) to 54F (4 OAT). CWST reset Lower CWST from 85F to 75F. CT fan VFD Add VFD to CT fan. 8% VFD efficiency. 14 of 14