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Home My WebLink About20260909Exhibit No. 1 - Water Heather TRM Update Memo.pdf EXHIBIT No. I CASE No.INT-G-26-05 INTERMOUNTAIN GAS COMPANY WATER HEATER TRM UPDATE MEMO (5 PAGES Intermountain Gas Commercial Water Heater TRM Update Memo 6/26/2026 Overview Qualus developed measure savings estimates for Intermountain Gas Company's (IGC) Commercial Technical Reference Manual(TRM) in 2023 and 2024. These savings estimates were based on a variety of sources including the Regional Technical Forum (RTF), the Illinois TRM, and the California electronic TRM (CA eTRM). As a part of a request to revise their General Service Energy Efficiency Rebate Program Rate Schedule, IGC shared their Commercial TRM with the Idaho Public Utilities Commission (IPUC)for review and approval. In their"INT-G-25-07"comments, the IPUC identified concerns regarding the savings estimates presented in the TRM for commercial storage and tankless water heaters. Original savings estimates for these measures were developed under the assumption that large commercial& industrial water heater equipment would be installed in IGC's service territory.The IPUC meanwhile, assumed that most instances of efficient gas water heater installations would be in light commercial settings. In light of these concerns, Qualus has updated the savings estimates for storage and tankless water heaters to better reflect the high prevalence of light commercial installations in IGC's service territory. Specifics regarding the process Qualus used to update these measures are outlined in the following section. TRM Update Process To update the savings estimates for the storage and tankless water heater measures included in IGC's Commercial TRM, Qualus referenced data from the CA eTRM as well as the Northwest Energy Efficiency Alliance's (NEEA) 2019 Commercial Building Stock Assessment (CBSA). More specifically, Qualus utilized the"EnergylmpactWH"files within the tankless' and storage water heater measure packages. These files contain savings estimates per kBTU/h input capacity for a variety of different gas water heater installations across various California climate zones and facility types. Qualus calculated a weighted average savings per kBTU/h input capacity value for both storage and tankless water heaters and then applied that weighted average to the median input capacity of water heaters per the 2019 CBSA. The calculations necessary to produce this savings estimate are presented in the following paragraphs. ' https://www.caetrm.com/measure/SWWHO06/10/ 2 https://www.caetrm.com/measure/SWWHO07/08/ The 2019 CBSA contains a variety of information on the facilities and energy-using equipment installed in Washington, Oregon, Idaho, and Montana. For the purposes of this analysis, Qualus focused exclusively on customers in Idaho within the CBSA's dataset on commercial water heaters. This Idaho-specific dataset included information on 82 commercial facilities with storage water heaters and five facilities with tankless water heaters. The CBSA was designed to be a regionally representative sample of commercial buildings based on cataloguing of all commercial buildings in the region. As such, Qualus used the CBSA as a reference point for likely IGC program participants. Qualus extracted several key datapoints from the CBSA dataset including the proportion of facility types, the proportion of facilities with large vs. small water heaters, and the median kBTU/hr input capacity of water heaters. Qualus matched CBSA facility types to the facility types listed in the CA eTRM and then used the proportion of those CBSA facility types to calculate a weighted average of savings. Per the CA eTRM's definitions, Qualus defined storage water heaters with a kBTU/h input capacity greater than 75 and tankless water heaters with a kBTU/h input capacity greater than 200 as large water heaters. Using these cutoff points, Qualus calculated the proportion of large vs. small water heaters in the CBSA and integrated that proportion into weighted average savings calculations. After calculating a weighted average savings per kBTU/h input capacity based on CBSA facility types and water heater sizes, Qualus was left with a savings per kBTU/h value for existing and new water heaters in each CA climate zone. After reviewing the CA climate zones, Qualus decided to only include zones 1, 2, 4, 5, 11, 12, and 16 in the analysis, based on the logic that those regions in Northern California likely have weather patterns most similar to Idaho. A map of CA climate zones is presented in Figure 1. Figure 1. California Climate Zones 1 16 12 3 -- -� ^i, 16 4� 16 �,_13 6 15 (> 9 8 714 15 The penultimate step in Qua[us' updated calculation of commercial water heater savings was employing typical meteorological year(TMY) heating degree day(HDD) data from representative weather stations to calculate a single savings per kBTU/h per HDD value per a linear regression analysis.Working under the assumption that many commercial water heaters are in unconditioned spaces, Qualus determined that adjusting for differences in HDD between California and Idaho was a key component in ensuring the final savings estimate was applicable to IGC's service territory. Qualus ran linear regressions for both retrofit and new construction scenarios and extrapolated the results of those regressions to the weighted average HDD of Boise, Twin Falls, and Idaho Falls weather stations, consistent with analysis methodology employed in the initial version of the IGC Commercial TRM.This calculation yielded savings per kBTU/h input capacity values for retrofit and new construction scenarios for both storage and tankless water heaters in IGC's service territory.While these savings per input capacity values are valid and could be used by themselves, Qualus also calculated savings per water heater values based on CBSA data. For this final step in the analysis, Qualus calculated the median kBTU/h input capacity of water heaters included in the CBSA dataset and used that median value to determine a single average savings value for retrofit and new construction scenarios for storage and tankless water heaters. In this manner, Qualus calculated updated savings values for commercial storage and tankless water heaters for IGC's TRM.These updated savings values should be more representative of the light commercial water heaters that the IPUC expects to be installed in IGC's service territory.