Comment #1Amendment: Proposed Amendment on Adjustment of Instantaneous Water Heater EfficiencyPage Number: 1Comment Type: GeneralComment:In general I don't doubt this is an adjustment that should be made. However, I think there are several other scenarios regarding DHW that the RESNET standard must address (eg Indirect-fired storage tank and combined appliance DHW efficiency). Without addressing those at the same time as this we would be penalizing instantaneous water heaters without considering whether other systems are being accurately represented. At the very least RESNET could provide a standard for determining an efficiency for those other systems at this same time. Making rules like this also opens up the discussion that we may not be accurately representing other things like condensing gas boilers in instances where a high temperature distribution is used. Is a boiler really 95% efficient when using high temp baseboard? I like to see RESNET addressing these issues but I think a more comprehensive view of all technologies (at least within a particular group - like DHW) would better serve the industry and result in more consistent ratings over time than making one change this year and another next year.Justification for Change:consistency and fairnessProposed Change:Review all other DHW technologies and modify RESNET standard to include guidance and/or automatic decreases in efficiency for all common modern DHW system types.
In general I don't doubt this is an adjustment that should be made. However, I think there are several other scenarios regarding DHW that the RESNET standard must address (eg Indirect-fired storage tank and combined appliance DHW efficiency). Without addressing those at the same time as this we would be penalizing instantaneous water heaters without considering whether other systems are being accurately represented. At the very least RESNET could provide a standard for determining an efficiency for those other systems at this same time.
Making rules like this also opens up the discussion that we may not be accurately representing other things like condensing gas boilers in instances where a high temperature distribution is used. Is a boiler really 95% efficient when using high temp baseboard?
I like to see RESNET addressing these issues but I think a more comprehensive view of all technologies (at least within a particular group - like DHW) would better serve the industry and result in more consistent ratings over time than making one change this year and another next year.
consistency and fairness
Review all other DHW technologies and modify RESNET standard to include guidance and/or automatic decreases in efficiency for all common modern DHW system types.
Comment #2Amendment: Proposed Amendment on Adjustment of Instantaneous Water Heater EfficiencyPage Number: 1Comment Type: TechnicalComment: Strioke any language referring to tankless water heaters as instantaneous.Justification for Change: Tankless water heaters are not instataneous and continuing to call them as such perpetuates the myth that that they are.
Strioke any language referring to tankless water heaters as instantaneous.
Tankless water heaters are not instataneous and continuing to call them as such perpetuates the myth that that they are.
Comment #3Amendment: Proposed Amendment on Adjustment of Instantaneous Water Heater EfficiencyPage Number: 1Comment Type: GeneralComment:Bradford White Corporation (BWC) recommends that all references to “instantaneous” should be changed to “tankless.” BWC strongly agrees with RESNET’s proposal to apply an adjustment factor of 0.92 to tankless water heaters. In addition to the lab and field testing conducted by Davis Energy Group (DEG) and the California Energy Commission (CEC), BWC has performed its own testing. Our testing agrees with the DEG and CEC studies. In fact, our results show that tankless water heaters, when operated in real world applications, operate consistently 9-10% low versus their rated Energy Factor.Justification for Change:The editorial change, above, is the appropriate term, as these types of water heaters do not generate hot water immediately when a water draw occurs. BWC’s other comments are in support of RESNET’s recommended changes. This support is based upon testing performed by BWC, as well as other studies performed by independent parties.
Bradford White Corporation (BWC) recommends that all references to “instantaneous” should be changed to “tankless.”
BWC strongly agrees with RESNET’s proposal to apply an adjustment factor of 0.92 to tankless water heaters. In addition to the lab and field testing conducted by Davis Energy Group (DEG) and the California Energy Commission (CEC), BWC has performed its own testing. Our testing agrees with the DEG and CEC studies. In fact, our results show that tankless water heaters, when operated in real world applications, operate consistently 9-10% low versus their rated Energy Factor.
The editorial change, above, is the appropriate term, as these types of water heaters do not generate hot water immediately when a water draw occurs.
BWC’s other comments are in support of RESNET’s recommended changes. This support is based upon testing performed by BWC, as well as other studies performed by independent parties.
Comment #4Amendment: Proposed Amendment on Adjustment of Instantaneous Water Heater EfficiencyPage Number: 1Comment Type: GeneralComment: In general, I support the idea of adjusting rated EF values to reflect real world performance and I am aware of the effects that reduce the actual installed performance of tankless water heaters. I conducted a residential water heating field study at the Center for Energy and Environment in Minnesota. This study looked at the installed performance of non-condensing and condensing tankless water heaters, as well as storage type water heaters. Our study showed installed efficiencies lower than the EF ratings of all models, not just the tankless models. The full project report is available at http://mncee.org/Innovation-Exchange/Reports-and-Technical-Documents/Actual-Savings-and-Performance-of-Natural-Gas-Tank/ As your proposed amendment says tankless water heaters lose efficiency due to small draws that are not reflected in the DOE profile. Tank type water heaters often had larger idle losses than expected and were affected by the total daily volume. Our study, as well as others, has shown that the 64.3 gallons per day daily usage of the Energy Factor test is higher than realistic usage rates. Higher daily volumes result in less idle time and better performance for tank type water heaters. The EF test was not designed to reflect real world performance, but to be used as a comparative performance metric. This performance meter has some significant problems, but to adjust the performance of only a single type of DHW appliance to reflect real world results would be unfair and would result in a loss of product neutrality.
In general, I support the idea of adjusting rated EF values to reflect real world performance and I am aware of the effects that reduce the actual installed performance of tankless water heaters. I conducted a residential water heating field study at the Center for Energy and Environment in Minnesota. This study looked at the installed performance of non-condensing and condensing tankless water heaters, as well as storage type water heaters. Our study showed installed efficiencies lower than the EF ratings of all models, not just the tankless models. The full project report is available at http://mncee.org/Innovation-Exchange/Reports-and-Technical-Documents/Actual-Savings-and-Performance-of-Natural-Gas-Tank/
As your proposed amendment says tankless water heaters lose efficiency due to small draws that are not reflected in the DOE profile. Tank type water heaters often had larger idle losses than expected and were affected by the total daily volume. Our study, as well as others, has shown that the 64.3 gallons per day daily usage of the Energy Factor test is higher than realistic usage rates. Higher daily volumes result in less idle time and better performance for tank type water heaters.
The EF test was not designed to reflect real world performance, but to be used as a comparative performance metric. This performance meter has some significant problems, but to adjust the performance of only a single type of DHW appliance to reflect real world results would be unfair and would result in a loss of product neutrality.
Comment #5Amendment: Proposed Amendment on Adjustment of Instantaneous Water Heater EfficiencyPage Number: AllComment Type: GeneralComment:Gas Instantaneous Water Heaters Bosch does not support the RESNET amendment on Instantaneous Water Heater Efficiency. Any time you apply a draw pattern to a given water heating technology, there are advantages and disadvantages for that technology. The Davis Energy Group study from 2007 consisted of field testing at one location with one tank style water heater and one gas instantaneous water heater. The instantaneous water heater in question was a non-condensing instantaneous with a staged burner. This particular technology has a normal efficiency curve – higher efficiency at higher flow rate (as shown in the Davis Energy Group study). Not every instantaneous water heater has this efficiency curve or technology strategy. Bosch instantaneous water heaters for example use a non-staged modulating burner that actually results in an inverse efficiency curve. One of Bosch’s condensing instantaneous water heaters for example has its highest efficiency at its lowest input rate – 98%. The Davis Energy Group estimates instantaneous water heater efficiency at minimum fire to be closer to 28%. A much more comprehensive study for the Minnesota Office of Energy Security additionally debunks the issue of short water draws. In fact the study showed that a switching from a tank water heater to a tankless water heater increased draw duration. Overall water usage marginally increased in some households and decreased in another. While this is bad from a water usage perspective, it shows that the Davis Energy Group’s conclusion on draw patterns resulting in an 8.8% de-rate are not accurate for a household switching from tank to instantaneous as the flow durations actually increase. Additionally they found that approximately 80% of sequential hot water draws occurred within 1 minute of the previous draw. From this, it becomes apparent the proposed amendment is heavily biased toward one style of instantaneous water heater design, and will be blindly applied to all instantaneous units based on extremely limited quantitative data. This will unfairly punish manufacturers of instantaneous water heaters that use alternative technologies compared to the one water heater tested by Davis Energy Group. Electric Tankless Water Heaters Bosch also does not support the RESNET amendment as it pertains to the application of the amendment to electric instantaneous products. The proposed amendment would subtract 8% from the Energy Factor of an electric instantaneous water heater. The only electric instantaneous products with an energy factor are those with inputs of 12kW and below. These products are not centralized water heating systems! These products are point of use systems with much smaller “heat exchangers” which result in less thermal loss than a larger central system water heater. Furthermore, these products should actually have their EF increased by a factor because they completely eliminate distribution losses when compared to a centralized water heating system (estimated by Davis Energy Group at 15 to 30 Therms per year). These losses are not accounted for in the EF test method. In closing, rather than apply a blanket adjustment to all models of a given technology we should be fixing the root cause of any discrepancy, the Energy Factor test method. The Energy Factor was never meant to be a real world efficiency measure. Rather it was meant to be a method for quick consumer comparison between models.
Gas Instantaneous Water Heaters
Bosch does not support the RESNET amendment on Instantaneous Water Heater Efficiency.
Any time you apply a draw pattern to a given water heating technology, there are advantages and disadvantages for that technology. The Davis Energy Group study from 2007 consisted of field testing at one location with one tank style water heater and one gas instantaneous water heater. The instantaneous water heater in question was a non-condensing instantaneous with a staged burner. This particular technology has a normal efficiency curve – higher efficiency at higher flow rate (as shown in the Davis Energy Group study). Not every instantaneous water heater has this efficiency curve or technology strategy. Bosch instantaneous water heaters for example use a non-staged modulating burner that actually results in an inverse efficiency curve. One of Bosch’s condensing instantaneous water heaters for example has its highest efficiency at its lowest input rate – 98%. The Davis Energy Group estimates instantaneous water heater efficiency at minimum fire to be closer to 28%.
A much more comprehensive study for the Minnesota Office of Energy Security additionally debunks the issue of short water draws. In fact the study showed that a switching from a tank water heater to a tankless water heater increased draw duration. Overall water usage marginally increased in some households and decreased in another. While this is bad from a water usage perspective, it shows that the Davis Energy Group’s conclusion on draw patterns resulting in an 8.8% de-rate are not accurate for a household switching from tank to instantaneous as the flow durations actually increase. Additionally they found that approximately 80% of sequential hot water draws occurred within 1 minute of the previous draw.
From this, it becomes apparent the proposed amendment is heavily biased toward one style of instantaneous water heater design, and will be blindly applied to all instantaneous units based on extremely limited quantitative data. This will unfairly punish manufacturers of instantaneous water heaters that use alternative technologies compared to the one water heater tested by Davis Energy Group.
Electric Tankless Water Heaters
Bosch also does not support the RESNET amendment as it pertains to the application of the amendment to electric instantaneous products. The proposed amendment would subtract 8% from the Energy Factor of an electric instantaneous water heater. The only electric instantaneous products with an energy factor are those with inputs of 12kW and below. These products are not centralized water heating systems! These products are point of use systems with much smaller “heat exchangers” which result in less thermal loss than a larger central system water heater. Furthermore, these products should actually have their EF increased by a factor because they completely eliminate distribution losses when compared to a centralized water heating system (estimated by Davis Energy Group at 15 to 30 Therms per year). These losses are not accounted for in the EF test method. In closing, rather than apply a blanket adjustment to all models of a given technology we should be fixing the root cause of any discrepancy, the Energy Factor test method. The Energy Factor was never meant to be a real world efficiency measure. Rather it was meant to be a method for quick consumer comparison between models.
Comment #6Amendment: Proposed Amendment on Adjustment of Instantaneous Water Heater EfficiencyPage Number: AllComment Type: TechnicalComment:Rinnai strongly recommends that the committee reject the proposal to amend Instantaneous (Tankless) Water Heater Efficiency. There has been clear evidence with the studies that been carried out the current federal government efficiency test does not represent true in house efficiency levels due to its limited six equal draw simulated use test. This has spurred several groups, including ASHRAE, AHRI and DOE, to begin development of a new simulated use test that would provide more realistic efficiency levels observed in consumer homes. In review of the studies presented for this proposal it is clear that the only evaluation considered was the “real use” efficiency of tankless water heaters versus the federal EF which utilizes the six equal draws. No direct comparison was made for storage water heaters “real use” efficiency versus the federal EF six equal draws. Since the federal EF test is a simulated use test, any change in daily draw volumes or draw patterns will definitely affect the resultant efficiency level of BOTH Storage and Tankless water heaters as mentioned below. Additional studies that actually compare “real use” efficiencies between storage and tankless water heaters such as “Actual Savings and Performance of Natural Gas Instantaneous Water Heaters” by ASHRAE members Ben Shoenbaurer, Martha Hewett and Dave Bohac should also be reviewed to understand that both storage and tankless water heaters actually perform below their federal EF performance level. This study compared storage to tankless in ten actual households using 24 different water heaters over a period of 15 months alternating the storage water heater with the tankless allowing both technologies under the same conditions. The results of this study show that tankless water heaters used anywhere between 22% to 63% less energy than the storage water heaters, saving on average 57 to 74 therms per year. Even though this study concluded that tankless water heaters had real use efficiency on average 10% less than the federal EF, Storage water heaters real use efficiency was even lower at an on average of 19% less than the federal EF. This real world study utilizing varying sites, different household size, varied daily water demand and draw patterns shows that even with the flaws of the current water heater efficiency test it does accurately predict the amount of savings a consumer can expect when using a tankless water heater in lieu of a storage tank water. When calculating the energy consumed per year utilizing the current EF test a 0.62 storage water heater will use 243 therms per year and a 0.82 tankless water heater will use 183 therms per year or a savings of 59 therms per year or nearly identical to the results of the Shoenbaurer study. Reviewing the original Davis Energy Study (Field ad Laboratory Testing of Tankless Gas Water Heater Performance, April 14, 2006) that the NREL report was based on shows several limitations that need to be considered. First, the study was based on a sample size of two units. One was used for field evaluation and modeled a house of two working adults with a small daily hot water load showing that both the tankless and storage water heater performed below the EF efficiency levels. The second unit was evaluated in a laboratory environment and was a tankless water heater from 2004 and was from a manufacturer with a small market presence and thus cannot be concluded as indicative of the market. As mentioned in the study there were some limitations in the test setup which could impact efficiency as well. The DOE has recently published a RFI indicating that they have begun their evaluation of the current test method for rating residential water heaters. This in addition to pending legislation H.R. 382 or the water heater rating improvement act which will mandate DOE to update the current test method to more accurately reflect the various water heaters on the market show that the issues with the current EF test predicting actual use water heater efficiency is being addressed. Considering the fact that more accurate methods for evaluating efficiency are being developed and should be available soon, reducing EF of tankless water heaters would be biased towards tankless water heaters. Based on these facts we recommend that the current proposal should be rejected until a broader consensus on this issue is achieved. Justification for Change:Studies referenced for justification of the proposed change only present information on instantaneous (tankless) water heaters and a more comprehensive study of all technologies EF ratings would be needed to accurately compare all types of water heaters and apply an adjustment to any type of water heating technology.Proposed Change:Reject the proposed amendment
Rinnai strongly recommends that the committee reject the proposal to amend Instantaneous (Tankless) Water Heater Efficiency.
There has been clear evidence with the studies that been carried out the current federal government efficiency test does not represent true in house efficiency levels due to its limited six equal draw simulated use test. This has spurred several groups, including ASHRAE, AHRI and DOE, to begin development of a new simulated use test that would provide more realistic efficiency levels observed in consumer homes. In review of the studies presented for this proposal it is clear that the only evaluation considered was the “real use” efficiency of tankless water heaters versus the federal EF which utilizes the six equal draws. No direct comparison was made for storage water heaters “real use” efficiency versus the federal EF six equal draws. Since the federal EF test is a simulated use test, any change in daily draw volumes or draw patterns will definitely affect the resultant efficiency level of BOTH Storage and Tankless water heaters as mentioned below.
Additional studies that actually compare “real use” efficiencies between storage and tankless water heaters such as “Actual Savings and Performance of Natural Gas Instantaneous Water Heaters” by ASHRAE members Ben Shoenbaurer, Martha Hewett and Dave Bohac should also be reviewed to understand that both storage and tankless water heaters actually perform below their federal EF performance level. This study compared storage to tankless in ten actual households using 24 different water heaters over a period of 15 months alternating the storage water heater with the tankless allowing both technologies under the same conditions. The results of this study show that tankless water heaters used anywhere between 22% to 63% less energy than the storage water heaters, saving on average 57 to 74 therms per year. Even though this study concluded that tankless water heaters had real use efficiency on average 10% less than the federal EF, Storage water heaters real use efficiency was even lower at an on average of 19% less than the federal EF. This real world study utilizing varying sites, different household size, varied daily water demand and draw patterns shows that even with the flaws of the current water heater efficiency test it does accurately predict the amount of savings a consumer can expect when using a tankless water heater in lieu of a storage tank water. When calculating the energy consumed per year utilizing the current EF test a 0.62 storage water heater will use 243 therms per year and a 0.82 tankless water heater will use 183 therms per year or a savings of 59 therms per year or nearly identical to the results of the Shoenbaurer study.
Reviewing the original Davis Energy Study (Field ad Laboratory Testing of Tankless Gas Water Heater Performance, April 14, 2006) that the NREL report was based on shows several limitations that need to be considered. First, the study was based on a sample size of two units. One was used for field evaluation and modeled a house of two working adults with a small daily hot water load showing that both the tankless and storage water heater performed below the EF efficiency levels. The second unit was evaluated in a laboratory environment and was a tankless water heater from 2004 and was from a manufacturer with a small market presence and thus cannot be concluded as indicative of the market. As mentioned in the study there were some limitations in the test setup which could impact efficiency as well.
The DOE has recently published a RFI indicating that they have begun their evaluation of the current test method for rating residential water heaters. This in addition to pending legislation H.R. 382 or the water heater rating improvement act which will mandate DOE to update the current test method to more accurately reflect the various water heaters on the market show that the issues with the current EF test predicting actual use water heater efficiency is being addressed. Considering the fact that more accurate methods for evaluating efficiency are being developed and should be available soon, reducing EF of tankless water heaters would be biased towards tankless water heaters. Based on these facts we recommend that the current proposal should be rejected until a broader consensus on this issue is achieved.
Studies referenced for justification of the proposed change only present information on instantaneous (tankless) water heaters and a more comprehensive study of all technologies EF ratings would be needed to accurately compare all types of water heaters and apply an adjustment to any type of water heating technology.
Reject the proposed amendment
Comment #7Amendment: Proposed Amendment on Adjustment of Instantaneous Water Heater EfficiencyPage Number: 1Comment Type: GeneralComment:Rheem Manufacturing Company strongly disagrees with RESNET’s proposal to adjust the Energy Factor for gas, oil, and electric instantaneous (Tankless) water heaters. The justification to use the Davis Energy Group (DEG) study as the basis of re-rating Tankless is inappropriate. Given that the study was admittedly non-comprehensive utilizing limited field and lab testing data with a very narrow range of products. Furthermore, the empirical study assumed “representative” daily load profiles and “hot/cold” weighting factors to determine the reduced efficiency rating which we believe may not reflect realistic hot water use. The DEG report recommended further study involving detailed testing on a wide range of Tankless units currently on the market to improve the understanding of “real world” performance. It is therefore premature to penalize instantaneous water heaters as a single product segment when there is further research needed. We would like to bring to RESNET’s attention that further research on daily water use and draw profiles is the subject of research already on-going by the Department of Energy (DOE), ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers), and AHRI (the Air-Conditioning, Heating, and Refrigeration Institute) for all water heaters. These efforts will serve to improve the DOE procedures to more closely reflect typical residential use. Given the limited scope of the DEG study, applying RESNET’s proposal at this time risks singling out instantaneous water heaters and imposes unreasonable de-rating. Unlike many other companies, Rheem is technology-neutral providing many water heater solutions including instantaneous and storage-type products. We would like to see a fair and balance treatment relying on a more comprehensive and scientific assessment. There are no doubt competitive elements that would desire to downgrade instantaneous water heaters at the expense of storage tank products. In closing, we strongly oppose the RESNET proposal to apply an adjustment factor of 0.92 to the instantaneous (gas, oil, electric) Energy Factor and recommend reconsideration pending completion work by the DOE and the industry. Justification for Change:Insufficient supporting data & consistency
Rheem Manufacturing Company strongly disagrees with RESNET’s proposal to adjust the Energy Factor for gas, oil, and electric instantaneous (Tankless) water heaters. The justification to use the Davis Energy Group (DEG) study as the basis of re-rating Tankless is inappropriate. Given that the study was admittedly non-comprehensive utilizing limited field and lab testing data with a very narrow range of products. Furthermore, the empirical study assumed “representative” daily load profiles and “hot/cold” weighting factors to determine the reduced efficiency rating which we believe may not reflect realistic hot water use. The DEG report recommended further study involving detailed testing on a wide range of Tankless units currently on the market to improve the understanding of “real world” performance. It is therefore premature to penalize instantaneous water heaters as a single product segment when there is further research needed.
We would like to bring to RESNET’s attention that further research on daily water use and draw profiles is the subject of research already on-going by the Department of Energy (DOE), ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers), and AHRI (the Air-Conditioning, Heating, and Refrigeration Institute) for all water heaters. These efforts will serve to improve the DOE procedures to more closely reflect typical residential use. Given the limited scope of the DEG study, applying RESNET’s proposal at this time risks singling out instantaneous water heaters and imposes unreasonable de-rating. Unlike many other companies, Rheem is technology-neutral providing many water heater solutions including instantaneous and storage-type products. We would like to see a fair and balance treatment relying on a more comprehensive and scientific assessment. There are no doubt competitive elements that would desire to downgrade instantaneous water heaters at the expense of storage tank products.
In closing, we strongly oppose the RESNET proposal to apply an adjustment factor of 0.92 to the instantaneous (gas, oil, electric) Energy Factor and recommend reconsideration pending completion work by the DOE and the industry.
Insufficient supporting data & consistency
Comment #8Amendment: Proposed Amendment on Adjustment of Instantaneous Water Heater EfficiencyPage Number: 1Comment Type: GeneralComment: In general support of comment #5, the studies referred to in the proposed amendment tested (I believe) only 2 heaters in-situ, and up to 5 total. While their analysis was helpful in defining the problem, I don't think it established a hard relationship between EF and effective efficiency. The reported results ranged between a 5% reduction and a 9% reduction. While it was implied that the internal capacity ranged from 0.1 and 1.0 gallons, and that losses in the unit were part of the issue, the tested unit in one study didn't have a measured water content. Finding other parameters (such as heat exchanger type and water content capacity) to drive the efficiency drop should be part of the amendment. I appreciate the need to revisit modeled efficiencies for various DHW, based on EF, technology, tank size, etc. I suggest we reject this amendment, and do a more comprehensive analysis of DHW technologies, looking at multiple system types (Storage/Tankless/Indirect) and multiple brands and models, and amend the standard accordingly. On a side note: with respect to electric resistance water heating, is there really a drop in efficiency before "steady state?" If so, is it anywhere close to the curve for combustion appliance heat exchange?Justification for Change: the amendement targets one technology, while exposing issues with rating all technologies.Proposed Change:reject this amendment, and follow a more comprehensive review of multiple brands and multiple types (tankless/storage-type/indirect-fired)
the amendement targets one technology, while exposing issues with rating all technologies.
reject this amendment, and follow a more comprehensive review of multiple brands and multiple types (tankless/storage-type/indirect-fired)
Comment #9Amendment: Proposed Amendment on Adjustment of Instantaneous Water Heater EfficiencyPage Number: 1Comment Type: TechnicalComment:Ending on November 28th, 2011, the Department of Energy (DOE) had an open Request for Information (RFI) concerning a modification to the current Test Procedure (TP) for the rating of residential water heaters (www.gpo.gov/fdsys/pkg/FR-2011-10-12/pdf/2011-25815.pdf). This RFI comes at the beginning of what the Gas Technology Institute (GTI) believes to be a serious and concerted effort to revise a test method that has been in place for over 15 years in its current form, and which is used as the primary metric for determining compliance with minimum energy efficiency standards, acceptance into the EnergyStar® program, and qualification for utility energy efficiency incentives. The revised DOE TP could be finalized as early as Q4 2012 and as late as Q4 2014, the former being driven by a U.S. Senate Bill under review, the Water Heater Rating Improvement Act of 2011 (D-WI). This RFI, released back on October 12th, 2011, comes at a time when several orgnizations, including ASHRAE, AHRI, and DOE/NIST are actively investigating potential improvements to the EF TP. If a “Simulated Use” test is retained for the revised TP, the current draw pattern will likely be replaced by a pattern that distributes the hot water volume in a greater number of draws over the 24 hour test, and possibly a few such patterns that vary in total daily hot water draw volume. Deviations from current Simulated Use TP Energy Factor (EF) rating will differ across equipment categories. Tankless water heaters will see across the board EF reductions as a result of the increased thermal cycling losses with a more distributed 24 hour hot water draw pattern. But a given volume storage water heater will also see EF reductions when tested at lower daily total hot water draw volumes as standby losses increase while hot water deliveries decrease. Based upon interactions with parties active in this revised TP development, the likelihood is that multiple draw patterns will be selected as an alternative to the current single draw pattern used. The multiple draw patterns will likely be categorized by daily total hot water usage, a low, medium, and high usage with the potential for the addition of a point-of-use draw pattern. The hot water draw pattern used in the current TP has been criticized for: Favoring tankless water heaters – One reason the current TP favors tankless water heaters is that they have minimal standby losses during the extended standby period. Additionally the six hot water draws are large volume draws, 10.7 gallons, which allow the tankless units to reach efficient steady state operation readily. Recent research suggests that both: (a) actual hot water use consists of numerous, small volume, short duration draws – estimates are an average of 79 draws/day at 0.7 gallons/draw [Thomas 2011]; and (b) intermittent draw patterns, like those observed in the field, can contribute to a substantial degradation of tankless water heater efficiency [Davis Energy Group 2006 & Schoenbauer et al. 2011]. Overestimating total daily usage – Residential hot water consumption differs from space heating loads, in that it is primarily affected by household size rather than building type or climate (i.e. groundwater temperature). Recent research from the Natural Resources Canada, whose original field research over 25 years ago provided the basis for the 64.3 gallons/day benchmark [Perlman & Mills 1985], found that over a 74 house field study the average total usage has dropped to 49 gallons/day [Thomas 2011]. This has an important effect on daily efficiency, as the proportional relationship of Delivered Efficiency/EF to daily hot water usage has been demonstrated repeatedly [Butcher 2010, Davis 2010, Glanville 2011]. Acknowledging these two deficiencies of the current TP, particularly the deviation between the rated and actual performance of tankless water heaters, California and Florida have modified their building codes to compensate. In California, the 2008 update to their building code mandated that a derating factor be applied to the EF of all tankless water heaters to more appropriately reflect actual performance in homes by taking into account the impact of hot water draws of small duration and volume and the cooling down of the heat exchanger. The Davis Energy Group (DEG) monitored two tankless units – one placed in an existing home and one tested in DEG’s facility. The results of the analysis indicated that there was a degradation of the efficiency of tankless systems that depended upon the size of the hot water draw and the duration of time between draws, with the most substantial degradation occurring when there were long periods of time between small draws. The resulting recommendation, which was subsequently adopted within the revised Title 24 standard, was to apply a 0.92 derating factor to the rated EF of tankless systems. Following suit, based upon additional laboratory study [Colon 2010], Florida’s building code was recently modified to apply a 0.92 derating factor in the estimation of tankless water heater efficiency through their code compliance simulation tool, EnergyGauge. And now RESNET has likewise proposed implementing an automatic reduction of 92% on the rated Energy Factor of an instantaneous water heater in its Home Energy Rating System (HERS) software [RESNET 2011]. As recent research suggests that the average U.S. household requires less than 64.3 gallons of hot water per day prescribed in the current standard, invariably a revised TP will focus on smaller daily draw patterns. Additionally, as research simultaneously shows that the average household has numerous short duration, small volume hot water draws as opposed to six regular sustained draws, the revised draw patterns will capture this through increased draw number and intermittency. These two factors in a revised Simulated Use TP will contribute to a likely universal drop in the estimated efficiency of all water heaters. Although this may lead to a disproportionate efficiency rating reduction for tankless units for reasons discussed previously, given volume storage water heaters will also see EF reductions when tested at lower daily total hot water draw volumes as standby losses increase while hot water deliveries decrease. Based on data presented in GTI's response to the DOE RFI [Glanville 2011B], if the the 64.3 gal/day hot water draw is reduced to 49 gal/day, a given volume storage water heater EF could be derated by as much as a 0.96 multiplier and possibly more. References 10 CFR Part 430 Energy Conservation Program for Consumer Products: Test Procedure for Water Heaters. Bohac, D. et. al. “Actual Savings and Performance of Natural Gas Tankless Water Heaters”. Minnesota Center for Energy and Environment (2010). Butcher, T. “Measurement and Application of Performance Curves for Residential Water Heaters” Brookhaven National Laboratory. Presented at ASHRAE Annual Meeting, Albuquerque, NM, (2010). Butcher. T et al. “Application of Linear Input/Output Model to Tankless Water Heaters”, Brookhaven National Laboratory. Presented at ASHRAE Winter Meeting, Las Vegas, NV, 2011. Colon, C. and Parker, D.”Side-by-Side Testing of Water Heating Systems: results from the 2009-2010 Evaluation” Rpt. No. FSEC-CR-1856-10.pdf, Florida Solar Energy Center, Cocoa, FL (2010). Davis Energy Group (DEG), 2008 California Building Energy Efficiency Standards: Tankless Gas Water Heaters (2006). Davis, R and Leni-Konig, K. “Laboratory Testing of Residential Gas Water Heaters” PG&E ATS (2008). Davis, R. “Laboratory Evaluation and Field Testing of Residential Heat Pump Water Heaters” PG&E ATS (2010). Glanville, P. “Modified Simulated Use with Input/Output Method”. Gas Technology Institute, presented at the ASHRAE Summer Meeting (2010). Glanville, P. “Laboratory Characterization of Residential Electric Heat Pump Water Heaters”. Gas Technology Institute. Presented at the ACEEE Hot Water Forum (2011). Glanville, P. and Kosar D. Comment Submission in Response to the Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE) Request for Information (RFI) Docket Number EERE-2011-BT-TP-0042, Test Procedures for Residential Water Heaters, Direct Heating Equipment, and Pool Heaters, Novermber 28, 2011 (2011B). Healy, W, et al. “Input-Output Approach to Predicting the Energy Efficiency of Residential Water Heaters – Testing of Gas Tankless and Electric Storage Water Heaters”. ASHRAE Transactions 117 (2011). Healy, W.M. “Effect of Temperature Stratification Near Heating Elements on the Measured Energy Factors of Electric Water Heaters”. ASHRAE Transactions 114 (2) (2008). Kalensky, D. and Scott, S. “Water Heater Comparison Final Report” No. 20464, Gas Technology Institute, 2007. Perlman, M. and Mills, B.E. “Development of Residential Hot Water Use Patterns”. ASHRAE Transactions, Vol. 91, pp 657-679 (1985). RESNET. RESNET Proposes Amendment on Instantaneous Water Heater Efficiency. November 14, 2011. http://campaign.r20.constantcontact.com/render?llr=4xoe5idab&v=001aYDP54lNfT8iXcda-Kl9ov834jcjXXDQnJNzR1mImV_vNvC9s53yaKbnmkLipbUkg5oA6qB3vmYsZPoKOfppoWE7tpMsCIFYx1YhcaU7OC3gQ-mB4VYLLkwNBd4biTCr. Schoenbauer, B. et al. “Actual Savings and Performance of Gas Tankless Water Heaters” Minnesota Center for Energy and Environment. Presented at ASHRAE Winter Meeting, Las Vegas, NV (2011). Sparn, B. et al. “Laboratory Performance Evaluation of Residential Integrated Heat Pump Water Heaters”. National Renewable Energy Laboratory (2011). Thomas, M. et al. “A New Study of Hot Water Use in Canada” Natural Resources Canada. Presented at ASHRAE Winter Meeting, Las Vegas, NV (2011). Justification for Change:With an improved test procedure (TP) for rating water heater efficiency now under development and likley to be available in a couple of years or less, the residential marketplace would be better served if RESNET deferred any such selective water heater type EF derating at this time and awaited the outcome of the TP revision process. Field and lab studies have shown that not only are tankless water heaters generally lower in effciency under real world hot water use scenarios due to short cycling effects from more frequent and smaller draws, but given volume storage water heaters would also suffer reduced efficiency levels with more realistic, lower daily total hot water draw volumes due to increased standby losses under decreased hot water deliveries.
Ending on November 28th, 2011, the Department of Energy (DOE) had an open Request for Information (RFI) concerning a modification to the current Test Procedure (TP) for the rating of residential water heaters (www.gpo.gov/fdsys/pkg/FR-2011-10-12/pdf/2011-25815.pdf). This RFI comes at the beginning of what the Gas Technology Institute (GTI) believes to be a serious and concerted effort to revise a test method that has been in place for over 15 years in its current form, and which is used as the primary metric for determining compliance with minimum energy efficiency standards, acceptance into the EnergyStar® program, and qualification for utility energy efficiency incentives. The revised DOE TP could be finalized as early as Q4 2012 and as late as Q4 2014, the former being driven by a U.S. Senate Bill under review, the Water Heater Rating Improvement Act of 2011 (D-WI). This RFI, released back on October 12th, 2011, comes at a time when several orgnizations, including ASHRAE, AHRI, and DOE/NIST are actively investigating potential improvements to the EF TP.
If a “Simulated Use” test is retained for the revised TP, the current draw pattern will likely be replaced by a pattern that distributes the hot water volume in a greater number of draws over the 24 hour test, and possibly a few such patterns that vary in total daily hot water draw volume. Deviations from current Simulated Use TP Energy Factor (EF) rating will differ across equipment categories. Tankless water heaters will see across the board EF reductions as a result of the increased thermal cycling losses with a more distributed 24 hour hot water draw pattern. But a given volume storage water heater will also see EF reductions when tested at lower daily total hot water draw volumes as standby losses increase while hot water deliveries decrease.
Based upon interactions with parties active in this revised TP development, the likelihood is that multiple draw patterns will be selected as an alternative to the current single draw pattern used. The multiple draw patterns will likely be categorized by daily total hot water usage, a low, medium, and high usage with the potential for the addition of a point-of-use draw pattern. The hot water draw pattern used in the current TP has been criticized for:
Acknowledging these two deficiencies of the current TP, particularly the deviation between the rated and actual performance of tankless water heaters, California and Florida have modified their building codes to compensate. In California, the 2008 update to their building code mandated that a derating factor be applied to the EF of all tankless water heaters to more appropriately reflect actual performance in homes by taking into account the impact of hot water draws of small duration and volume and the cooling down of the heat exchanger. The Davis Energy Group (DEG) monitored two tankless units – one placed in an existing home and one tested in DEG’s facility. The results of the analysis indicated that there was a degradation of the efficiency of tankless systems that depended upon the size of the hot water draw and the duration of time between draws, with the most substantial degradation occurring when there were long periods of time between small draws. The resulting recommendation, which was subsequently adopted within the revised Title 24 standard, was to apply a 0.92 derating factor to the rated EF of tankless systems. Following suit, based upon additional laboratory study [Colon 2010], Florida’s building code was recently modified to apply a 0.92 derating factor in the estimation of tankless water heater efficiency through their code compliance simulation tool, EnergyGauge. And now RESNET has likewise proposed implementing an automatic reduction of 92% on the rated Energy Factor of an instantaneous water heater in its Home Energy Rating System (HERS) software [RESNET 2011].
As recent research suggests that the average U.S. household requires less than 64.3 gallons of hot water per day prescribed in the current standard, invariably a revised TP will focus on smaller daily draw patterns. Additionally, as research simultaneously shows that the average household has numerous short duration, small volume hot water draws as opposed to six regular sustained draws, the revised draw patterns will capture this through increased draw number and intermittency. These two factors in a revised Simulated Use TP will contribute to a likely universal drop in the estimated efficiency of all water heaters. Although this may lead to a disproportionate efficiency rating reduction for tankless units for reasons discussed previously, given volume storage water heaters will also see EF reductions when tested at lower daily total hot water draw volumes as standby losses increase while hot water deliveries decrease. Based on data presented in GTI's response to the DOE RFI [Glanville 2011B], if the the 64.3 gal/day hot water draw is reduced to 49 gal/day, a given volume storage water heater EF could be derated by as much as a 0.96 multiplier and possibly more.
References 10 CFR Part 430 Energy Conservation Program for Consumer Products: Test Procedure for Water Heaters.
Bohac, D. et. al. “Actual Savings and Performance of Natural Gas Tankless Water Heaters”. Minnesota Center for Energy and Environment (2010).
Butcher, T. “Measurement and Application of Performance Curves for Residential Water Heaters” Brookhaven National Laboratory. Presented at ASHRAE Annual Meeting, Albuquerque, NM, (2010).
Butcher. T et al. “Application of Linear Input/Output Model to Tankless Water Heaters”, Brookhaven National Laboratory. Presented at ASHRAE Winter Meeting, Las Vegas, NV, 2011.
Colon, C. and Parker, D.”Side-by-Side Testing of Water Heating Systems: results from the 2009-2010 Evaluation” Rpt. No. FSEC-CR-1856-10.pdf, Florida Solar Energy Center, Cocoa, FL (2010).
Davis Energy Group (DEG), 2008 California Building Energy Efficiency Standards: Tankless Gas Water Heaters (2006).
Davis, R and Leni-Konig, K. “Laboratory Testing of Residential Gas Water Heaters” PG&E ATS (2008).
Davis, R. “Laboratory Evaluation and Field Testing of Residential Heat Pump Water Heaters” PG&E ATS (2010).
Glanville, P. “Modified Simulated Use with Input/Output Method”. Gas Technology Institute, presented at the ASHRAE Summer Meeting (2010).
Glanville, P. “Laboratory Characterization of Residential Electric Heat Pump Water Heaters”. Gas Technology Institute. Presented at the ACEEE Hot Water Forum (2011).
Glanville, P. and Kosar D. Comment Submission in Response to the Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE) Request for Information (RFI) Docket Number EERE-2011-BT-TP-0042, Test Procedures for Residential Water Heaters, Direct Heating Equipment, and Pool Heaters, Novermber 28, 2011 (2011B).
Healy, W, et al. “Input-Output Approach to Predicting the Energy Efficiency of Residential Water Heaters – Testing of Gas Tankless and Electric Storage Water Heaters”. ASHRAE Transactions 117 (2011).
Healy, W.M. “Effect of Temperature Stratification Near Heating Elements on the Measured Energy Factors of Electric Water Heaters”. ASHRAE Transactions 114 (2) (2008).
Kalensky, D. and Scott, S. “Water Heater Comparison Final Report” No. 20464, Gas Technology Institute, 2007.
Perlman, M. and Mills, B.E. “Development of Residential Hot Water Use Patterns”. ASHRAE Transactions, Vol. 91, pp 657-679 (1985).
RESNET. RESNET Proposes Amendment on Instantaneous Water Heater Efficiency. November 14, 2011. http://campaign.r20.constantcontact.com/render?llr=4xoe5idab&v=001aYDP54lNfT8iXcda-Kl9ov834jcjXXDQnJNzR1mImV_vNvC9s53yaKbnmkLipbUkg5oA6qB3vmYsZPoKOfppoWE7tpMsCIFYx1YhcaU7OC3gQ-mB4VYLLkwNBd4biTCr.
Schoenbauer, B. et al. “Actual Savings and Performance of Gas Tankless Water Heaters” Minnesota Center for Energy and Environment. Presented at ASHRAE Winter Meeting, Las Vegas, NV (2011).
Sparn, B. et al. “Laboratory Performance Evaluation of Residential Integrated Heat Pump Water Heaters”. National Renewable Energy Laboratory (2011).
Thomas, M. et al. “A New Study of Hot Water Use in Canada” Natural Resources Canada. Presented at ASHRAE Winter Meeting, Las Vegas, NV (2011).
With an improved test procedure (TP) for rating water heater efficiency now under development and likley to be available in a couple of years or less, the residential marketplace would be better served if RESNET deferred any such selective water heater type EF derating at this time and awaited the outcome of the TP revision process. Field and lab studies have shown that not only are tankless water heaters generally lower in effciency under real world hot water use scenarios due to short cycling effects from more frequent and smaller draws, but given volume storage water heaters would also suffer reduced efficiency levels with more realistic, lower daily total hot water draw volumes due to increased standby losses under decreased hot water deliveries.
Return to Proposed Amendment on Adjustment of Instantaneous Water Heater Efficiency