Draft PDS-01, RESNET/ICC 301-2022 Addendum F-202x, Integrated Heat Pump Water Heater

Entry Date: June 3, 2024 at 11:05 AM

Full Name: Paul Kintner

Affiliation: Ekotrope

Address: 19 Kingston St. Boston, Massachusetts 02111

Phone Number: (617) 863-7750

Email: paul@ekotrope.com

Page Number: 1

Section/Table/Figure Number: 1. Add definitions to Section 3.2 Definitions

Comment Intent: Not an Objection

Comment Type: Technical

Comment:

The definition for Split-System Heat Pump Water Heater, says “connected by refrigerant lines.” but these are very often connected via water lines. See the classic residential split system example here.

Proposed Change to Amendment:

Recommend changing the text to “connected by refrigerant or water lines.”

Entry Date: June 17, 2024 at 5:17 PM

Full Name: Shilpa Surana

Affiliation: 2050 Partners on behalf of California Investor Owned Utilities

Address: 81 Coral Drive Orinda, California 94563

Phone Number: 5039544711

Email: shilpasurana@2050partners.com

Page Number: 11

Section/Table/Figure Number: Section 3.2

Comment Intent: Not an Objection

Comment Type: Technical

Comment:

The proposed code change modifies the definition of heat pump water heater by making a reference to the consumer water heaters defined under USDOE 10 CFR 430. It also modifies the definition of heat pump water heater and integrated heat pump water heaters to add clarity to the requirements.

Proposed Change to Amendment:

1. Add definitions to Section 3.2 Definitions

Heat Pump Water Heater (HPWH) – A Heat Pump that is typically used to heat water for service hot water use. It may also be used for space heating.

Integrated Heat Pump Water Heater (iHPWH) – A Heat Pump Water Heater where all the components of the system are packaged in a single unit. This is distinct from a Split-System Heat Pump Water Heater. Most residential Heat Pump Water Heaters are Integrated.

Consumer Water Heater is a water heater that meets the definition of a consumer product under USDOE 10 CFR 430. 

Heat Pump Water Heater (HPWH) is a Consumer Water Heater that transfers thermal energy from one temperature level to another temperature level for the purpose of heating water, including all ancillary equipment such as fans, storage tanks, pumps, or controls necessary for the device to perform its function. 

INTEGRATED HEAT PUMP WATER HEATER (iHPWH) is a HPWH which has all components, including fans, storage tanks, pumps, or controls necessary for the device to perform its function contained in a single factory-made assembly.

Entry Date: June 17, 2024 at 5:57 PM

Full Name: Gary Klein

Affiliation: Self

Address: 11891 Autumn Sunset Way Rancho Cordova, California 95742

Phone Number: 9165497080

Email: gary@garykleinassociates.com

Page Number: 11

Section/Table/Figure Number: Section 3.2

Comment Intent: Objection

Comment Type: Technical

Comment:

1. Definitions

The code change recommends modifications to the definitions and acronyms. The different types of air source heat pump water heaters are shown as subsets of HPWH so that these related terms will be found next to each other. Air source has been added to the definitions to provide clarity that these requirements do not apply to ground or water source heat pump water heaters.

 

The draft standard contained two definitions for heat pump water heaters. They are straightforward, but not as clear as designers, installers, raters, and inspectors probably need.

 

1. Heat pump water heater. The proposal is based on the definition that comes from DOE.
2. Integrated heat pump water heater (iHPWH). There are two types of iHPWH. Those with electric resistance elements contained within the storage tank, and those without such elements.
   1. Please consider creating two definitions.
3. Split system heat pump water heater. There are two types of these too. Those with the evaporator separated from the condenser (similar to HVAC systems with indoor and outdoor units) and those with the evaporator and condenser combined into one piece of equipment that is generally installed outdoors.
   1. Please consider creating two definitions.

Proposed Change to Amendment:

1. Add definitions to Section 3.2 Definitions

 

Heat Pump Water Heater (HPWH) – A Heat Pump that is typically used to heat water for service hot water use. It may also be used for space heating.   A water heater that transfers thermal energy from one temperature level to another temperature level for the purpose of heating water, including all ancillary equipment such as fans, storage tanks, pumps, or controls necessary for the device to perform its function. These water heaters meet the definition of a consumer product under USDOE 10 CFR 430. Provisions for testing these water heaters are contained in Appendix E to Subpart B of Part 430.

 

1. Hybrid Integrated HPWH (iHPWH-Hybrid). The air-source heat pump is integrated into the unitary water heater, usually above the storage tank. There are electric resistance elements in the storage tank. The controls allow for heat pump only, heat pump and electric resistance, and electric resistance only.
2. Integrated HPWH (iHPWH). The air-source heat pump is integrated into the unitary water heater, usually above the storage tank. There are no electric resistance elements in the storage tank. The controls only allow for heat pump operation.
3. Air-Source HPWH Split (HPWH_S). The condenser and the evaporator of this type of air-source heat pump water heater are installed in separate locations. Refrigerant provides the energy transfer to the storage tank.
4. Air-Source HPWH Decoupled (HPWH_D). The condenser and the evaporator of this type of air-source heat pump water heater are installed in the same location (sometimes called monobloc). Water, with and without antifreeze, provides the energy transfer to the storage tank.

 

Integrated Heat Pump Water Heater (iHPWH) – A Heat Pump Water Heater where all the components of the system are packaged in a single unit. This is distinct from a Split-System Heat Pump Water Heater. Most residential Heat Pump Water Heaters are Integrated.

 

Split-System Heat Pump Water Heater – A Heat Pump Water Heater where some components are separated from each other, connected by refrigerant lines. These systems typically have a compressor and fan outside and a storage water tank inside.

Entry Date: June 17, 2024 at 6:00 PM

Full Name: Gary Klein

Affiliation: Self

Address: 11891 Autumn Sunset Way Rancho Cordova, California 95742

Phone Number: 9165497080

Email: gary@garykleinassociates.com

Page Number: 19

Section/Table/Figure Number: Section 3.3

Comment Intent: Objection

Comment Type: Technical

Comment:

1. Acronyms

The draft standard had two acronyms to match the definitions. The proposed language provides acronyms that match the proposed definitions.

1. Please consider using these acronyms.

Proposed Change to Amendment:

1. Add acronyms to Section 3.3 Acronyms

HPWH – Heat pump water heater

iHPWH – Air-source integrated heat pump water heater

iHPWH-Hybrid – Hybrid air-source integrated heat pump water heater

HPWH_S – Air-Source heat pump water heater: Split

HPWH_D – Air-Source heat pump water heater: Decoupled

Entry Date: June 17, 2024 at 6:10 PM

Full Name: Gary Klein

Affiliation: Self

Address: 11891 Autumn Sunset Way Rancho Cordova, California 95742

Phone Number: 9165497080

Email: gary@garykleinassociates.com

Page Number: 31

Section/Table/Figure Number: footnote ac for service water heating in Table 4.2.2(1)

Comment Intent: Objection

Comment Type: Technical

Comment:

1. Overview

Most readers know that I have been working for more than 30 years to improve the efficiency of hot water systems in our buildings. The key word is “systems”. The components all need to work well together to provide the customer the service of hot water.

 

These comments will focus on one component, air-source heat pump water heaters (AS_HPWH). In fact, most of the comments will be limited to integrated AS_HPWH. There are two types: Hybrid, which has electric resistance elements built into the storage tank, and those without such elements. Hybrid HPWH are the most commonly installed AS_HPWH in the US market at this time.

 

My ask is simple: Do not allow the performance of air-source heat pump water heaters to be degraded by allowing installations that restrict access to the “warm” air they need for efficient operation.

 

The purpose of this proposal is to ensure that AS_HPWH can always operate in heat pump mode. And operating at the highest COPs that can be achieved for each type of AS_HPWH. For the iHPWH and iHPWH-Hybrid units this means a COP of 3 or higher, which can be achieved when they are provided intake and ambient air conditions at or above those in the DOE method of test. Doing so will benefit consumers, policy makers, and environmentalists. Architects, builders, plumbers, inspectors and raters all play a part in ensuring that AS_HPWH can achieve their potential.

 

iHPWH and iHPWH-Hybrid need to have access to conditioned, or warmer air so that they can run in heat pump mode as many hours a day as needed to heat the water desired by the occupants.

 

The currently available iHPWH were developed by the water heater manufacturers in response to a change in the Federal efficiency requirements, and the test conditions and procedures were agreed to by a diverse group of industry participants. These same companies make the majority of the 9 million consumer product water heaters sold in the US every year. These are usually minimum efficiency gas or electric resistance storage water heaters. The Hybrid integrated HPWH that are on the market today are essentially electric resistance storage tank water heaters with a heat pump compressor on top of the tank and evaporator coils wrapped around the storage tank.

 

The initial versions of these hybrid integrated HPWH have relatively small compressors with heat rates of about 4,000-4,500 BTU per hour. This is much slower than the 4.5 kW@240VAC electric resistance elements that are about 15,000 BTU/hour. Whenever the inlet air temperature gets too low, or the demand for hot water is too large, the hybrid HPWH use the resistance elements. It is this hybrid feature that allows them to continue to heat water when operating conditions are colder than cutoff temperature of the heat pump.

 

What about iHPWH that do not have built-in resistance elements? Or those with larger compressors and correspondingly faster recover times? Or HPWH that have cutoff temperatures that allow them to operate as heat pumps using unconditioned air (cold-climate capable)? iHPWH without built-in elements and those with larger compressors are already being sold in the US. NEEA Advanced Water Heater Specification Version 8.1 includes provisions for rating split-system HPWH with a Cool Climate Efficiency metric that is used for indoor installations, thus accommodating a wider range of product configurations. In all these cases, the intention is to enable the HPWH to operate in heat pump mode using unconditioned air. Much less energy per gallon of hot water than resistance.

 

In summary, air source HPWH are not intended to be installed in unventilated enclosures. The proposed modifications to the standard will help ensure that they get access to the warm air they need to operate efficiently.

 

Unless the appropriate ventilation has been provided, or the HPWH is intended for “cold-climate” installations, the maximum allowable UEF for rating and modelling purposes shall be 2.0. A field rater can verify the installation meets the requirements.

1. Determining air flow requirements for ducted air source HPWH.

 

The energy supplied to the water by the heat pump is the sum of the thermal value of the electrical power of the compressor, fan, and controls and the heat extracted from the air. We can use the power consumption of the compressor, fan, and controls to develop a code minimum air flow rate. To ensure that there is enough air flow we will assume a COP of 3. This means that one-third of the energy supplied to the water comes from the electrical power and two-thirds comes from the air. This value will be used to set the minimum ducted ventilation air flow rates in the applicable code or standard.

 

Air-related Q = 1.08 x CFM x delta-T across the coil

Solving for CFM = Air-related Q/(1.08 x delta-T across the coil)

 

To get the CFM,

1. Identify the compressor, fan, and control power consumption in Watts.
2. Multiply the Watts by 3.412 to get electrical BTUs.
3. Assume a delta-T across the coil of 10F.
4. Assume a COP of 3. Multiply the electrical BTUs by 3 to get total thermal BTU.
5. Air-related BTU = Total Thermal BTU – Electrical BTU

 

Example: 4,000 BTU per hour HPWH have about 400 watts of electricity associated with the compressor, fan and controls.

 

400 x 3.412 = 1,365 BTU Electrical

 

1,365 x 3 = 4,095 BTU Total Thermal

 

4,095 – 1,365 = 2,730 BTU Air-Related

 

2,730 = 1.08 x CFM x 10

 

CFM = 2,730/(1.08 x 10) = 253 CFM

 

To get this proportional to every 100 watts of electrical power consumption, divide this value by 4.

253 CFM/4 = 63.5 CFM per 100 watts of compressor, fan, and control power consumption.

 

For simplicity, let’s round this down to 60 CFM per 100 watts.

 

 

1. Ensuring Access to Enough “Warm” Air

The key to an air-source heat pump water heater’s efficiency is to provide it with warm air for it extract heat from. Ideally, even Hybrid integrated heat pump water heaters will operate in heat pump mode as many hours a day as needed. Those without resistance backup need air that is warmer than the compressor cut-out temperature; for efficiency, the warmer the better.

 

How warm does the air need to be? The available consumer integrated HPWH are rated for efficiency in accordance with the procedures set forth in USDOE 10 CFR 430 Subpart B Section 2.2.2 which states that:

 

Heat Pump Water Heaters. The dry-bulb temperature shall be maintained at an average of 67.5 °F ± 1 °F (19.7 °C ± 0.6 °C) after a cut-in and before the next cut-out, an average of 67.5 °F ± 2.5 °F (19.7 °C ± 1.4 °C) after a cut-out and before the next cut-in, and at 67.5 °F ± 5 °F (19.7 °C ± 2.8 °C) on a continuous basis throughout the test. The relative humidity shall be maintained within a range of 50% ± 5% throughout the test, and at an average of 50% ± 2% after a cut-in and before the next cut-out.

 

This is roughly the temperature of conditioned air inside our buildings during winter weather, arguably a worst-case condition for performance. The relative humidity levels vary widely across the country. Where they are high, the latent heat will provide additional energy. For this discussion, it will be considered a benefit to the requirements for sensible heat transfer.

 

Under the DOE method of test, the cool exhaust air is not allowed to remain near the storage tank nor is it allowed to mix with the warm inlet air. The resulting Uniform Energy Factor (UEF) is based on this test procedure. While not an exact match for the UEF, the coefficient of performance (COP) is a related metric to rank the performance of the HPWH. Warmer intake air temperatures increase the COP. Colder intake air temperatures reduce the COP.

 

 

 

My recommendations on the need to ensure air flow are based on my review of the two Amazing Shrinking Room (ASR) reports, one by NEEA and one by PGE. As shown in Figure 20 from the PGE report, the COP stays above 3 when the intake air temperature is above 60F. When the intake air temperature gets below 58F, there is a combination of heat pump and resistance heating and around 50F the COP is below 2. When the intake air temperature gets below 45F, electric resistance heating dominates and the COP approaches 1, the same as an electric resistance water heater.

 

 

Source: Final Project Report Laboratory Testing of Heat Pump Water Heater Performance: Impact of Airflow and Space Configurations CR22PGE1901-1.

 

 

What would happen if the HPWH were not iHPWH-Hybrid units, or they were being operated in heat pump only mode? When the temperature dropped below the cut-out temperature, they would stop heating water, and would need to wait for the room to warm back up before they could continue.

 

If there is a large enough demand for hot water, installing an iHPWH in a small enclosure that only gets its energy via conduction eventually causes the temperature in that enclosure to drop below 58F, dramatically reducing the COP, while simultaneously increasing the cost to heat that water.

 

 

 

 

Figure 8 from the NEEA report shows that it takes roughly 2 hours, 15 minutes for the room temperature to recover after the heat pump has been extracting energy from the room for roughly 3 hours, 30 minutes. For simplicity, let’s say that it needs 2 hours to recover for every 3 hours of run time. Over a 24-hour day, this means that the maximum hours the AS_HPWH can run in an enclosed space is 16 hours. While this is potentially convenient for any demand reduction or load shifting programs, limiting the run time, limits the amount of energy the heat pump can make hot water.

 

 

Source: NEEA REPORT #E22-334 Heat Pump Water Heaters in Small Spaces Lab Testing: “The Amazing Shrinking Room”

 

The following excerpt from Comments on Consumer Product Heat Pump Water Heaters submitted by Gary Klein to CEC Docket 24-BSTD-01 continues the discussion as to the limitations on heat-pump only hot water production in a small enclosure. The full text can be found at TN256524_20240522T225245_Gary Klein and Associates, Inc.pdf

 

Room Size for Consumer Product Integrated HPWH

1. Unless the thermal resistance of the walls, floor and ceiling of the space surrounding a consumer product HPWH is R-2 or less, there is no size of small room that can get enough energy due solely to conduction to provide the energy needed for a 4,000 BTU/hour unit to operate as a heat pump 24 hours a day. The problem gets worse as the heat pump capacity gets larger.
   1. An R-2 enclosure is the equivalent of 1 inch of wood with stationary air films on both sides. Not a typical construction detail.
   2. An R-4 enclosure is what can be expected from 2×4 framing with sheet rock on both sides.
   3. An R-10 enclosure is the same construction with insulation between the framing members.
2. The temperature drop across the enclosed space must always be going into the room. Another way of saying this that the room with the heat pump only gains energy when it is colder that space that surrounds it.
   1. Consumer integrated HPWHs are intended to use conditioned air. In a 1-story dwelling the ceiling of the room will be insulated to at least R-30. If one of the walls is an exterior wall, that will be insulated to at least R-20. The floor may be insulated to R-20 or more.
   2. A room in the middle of the dwelling with a floor above and a conditioned basement below would be the best case for heat transfer into the room. Otherwise, more energy needs to come through the surfaces that are less well insulated.
   3. If these water heaters are installed in a garage they are exposed to outdoor conditions. They are not getting conditioned air at relatively stable and warm temperatures. Sometimes the temperature in the garage will be very warm, sometimes it will be very cold. And, the heat flow from outside will not always be into the garage.
3. Only a portion of the energy comes from the air, the rest comes from the heat pump. How much is the air’s contribution?
   1. Assumptions
      1. 400-watt compressor and fan = 1,365 BTU/hour
      2. COP = 3 (roughly true for 68-70F intake air)

• 1,365 x 3 = 4,094 BTU/hour

1. Energy supplied by the air = 4,094 – 1,365 = 2,730 BTU/hour

1. As the COP goes down, the air contributes less energy.
2. Unless the energy coming into the room via conduction is at least 2,730 BTU/hour, the water heater cannot run in heat pump mode continuously with a high COP.
   1. If continuous operation is not possible, the room will cool down, lowering both the COP and the heat output if the HPWH, which means it will take longer to recover.
   2. Eventually the heat pump mode will stop, and the room will take time to recover the heat that has been extracted.
      1. The ASR studies have shown that it takes at least 1 hour to recover for every 2 hours of heat pump operation. This means that the HPWH is limited to 16 hours a day.

• Limiting access to new warm air limits the gallons per day that can be heated by the HPWH.
  1. Let’s look at an R-4, 450 cubic foot enclosure. Assumptions:
     1. Ambient air temperature outside the enclosure is 70F. Same inside the enclosure at the start of an event.
     2. Assume there is a 20F delta-T into the room while the HPWH is running. This means that 1,783 BTU will come into the room every hour.
     3. For 16 hours of operation this will bring 28,528 BTU into the space. This energy will be extracted from the air by the HPWH.
     4. Over the same time, the compressor will add 16 x 1,365 BTU/hour = 21,840 BTU
     5. Total is 50,368 BTU. About 95 gallons per day. Any additional hot water needs to be heated using resistance heating.
  2. What about an R-10, 450 cubic foot enclosure? Assumptions:
     1. Ambient air temperature outside the enclosure is 70F. Same inside the enclosure at the start of an event.
     2. Assume there is a 20F delta-T into the room while the HPWH is running. This means that 770 BTU will come into the room every hour.
     3. For 16 hours of operation this will bring 12,320 BTU into the space. This energy will be extracted from the air by the HPWH.
     4. Over the same time, the compressor will add 16 x 1,365 BTU/hour = 21,840 BTU
     5. Total is 34,160 BTU. About 59 gallons per day. Any additional hot water needs to be heated using resistance heating.
  3. Which is the more likely enclosure? It doesn’t matter, both levels of insulation limit the amount of hot water made by the heat pump.
  4. 59-95 gallons per day may sound like a lot of hot water. But we do not know how much hot water is needed by the occupants.

 

Figure 15 from the NEEA report shows the interventions that were studied to mitigate the adverse effects of installing integrated air source HPWH in small enclosures. The installation requirements in this proposal have been selected to ensure that the integrated HPWH have a chance of operating as many hours a day as needed with a COP of 3 or more. These installation requirements are applicable to all air-source HPWH.

 

Source: NEEA REPORT #E22-334 Heat Pump Water Heaters in Small Spaces Lab Testing: “The Amazing Shrinking Room”

 

 

 

1. Can Conduction Alone Supply the Energy Needed for an Air-Source HPWH?

 

Assumptions

1. iHPWH need to run in heat pump mode to be the most efficient.
2. To perform as efficiently as measured during the DOE test conditions, the intake air needs to be at least 68F.
3. For a given capacity iHPWH (BTU/hour), the number of gallons per day that are needed determines the hours of operation.

 

The Problem with Conduction into a Small Room with iHPWH

1. Conduction only goes into the small room with the iHPWH when it is colder than the surrounding space.
2. The surrounding space needs to be at least 68F.
3. The rate of heat transfer into the small room depends on the R-value of the surfaces.
   1. A typical interior room has 2×4 walls with sheetrock on both sides, (roughly R-4). Floors and ceilings have different construction details.
   2. Insulation is often installed on interior walls, floors and ceilings for sound mitigation. HPWH make noise.
   3. It is bad practice for the code/standard to assume that the surfaces surrounding a small interior room are under-insulated.
4. The energy flow into the small room must be greater than or equal to the rate at which the heat pump extracts heat from the air.
   1. Otherwise, at some point the small room will get too cold and the heat pump will turn off.
   2. The room then needs to warm back up before the iHPWH can resume heating the water.
5. If electric resistance back up is available, it can then take over. But this is much less efficient. And much more expensive to operate.
6. If the daily hot water use is very large, the iHPWH may need to run all the time. The only way to accomplish this in heat pump mode is to ensure access to warm intake air, and to remove the cold discharge air from the small room.

 

Figure 1. Best Case. All Six surfaces of the small room are surrounded by conditioned rooms.

 

 

1. Unfortunately, the best case isn’t available to us in many buildings. Figures 2-9 show most of the more likely cases, where at least one of the six surfaces is not available for conduction, or can only provide energy via conduction intermittently. There is another likely case that isn’t shown: the iHPWH is installed in a corner room, with two exterior walls.
2. And, as will be shown later, relying solely on conduction through the surfaces into the small room reduces efficiency in heat pump mode to below COP-2. It also limits the amount of hot water that can be made each day.

Figure 2. The Unconditioned Basement is colder than the small room. One of the six surfaces can no longer contribute energy via conduction. The floor is shown as uninsulated, but it might be. The R-value of this uninsulated floor is roughly R-2.

 

 

 

Figure 3. The Unconditioned Crawlspace can be either hotter or colder than the small room. The floor of the small room will be insulated. The R-value of this surface is at least R-10. Very little conduction, even if the temperature differences are favorable.

 

 

 

Figure 4. The Slab Foundation is colder than the small room. One of the six surfaces can no longer contribute energy via conduction. The slab floor is shown as uninsulated, but it might be.

 

Figure 5. Both the Unconditioned Attic and the Unconditioned Crawlspace can be either hotter or colder than the small room. The ceiling of the small room is insulated to at least R-30. The floor is insulated to at least R-10. Very little conduction, even if the temperature differences are favorable. Two of the six surfaces cannot reliably contribute heat via conduction.

 

 

 

Figure 6. The Unconditioned Attic can be either hotter or colder than the small room. The ceiling of the small room is insulated to at least R-30. Very little conduction, even if the temperature differences are favorable. The Slab Foundation is colder than the small room. The slab floor is shown as uninsulated, but it might be.

 

 

 

Figure 7. Insulated External Wall. The outside can be either hotter or colder than the small room. The external wall of the small room is insulated to at least R-10. Very little conduction, even if the temperature differences are favorable.

 

 

 

Figure 8. The Unconditioned Attic (R-30), the Unconditioned Crawlspace (R-10) and the External Wall (R-10) can be either hotter or colder than the small room. Very little conduction, even if the temperature differences are favorable.

 

 

 

Figure 9. The Unconditioned Attic (R-30), and the External Wall (R-10) can be either hotter or colder than the small room. Very little conduction, even if the temperature differences are favorable. The Slab Foundation is colder than the small room. The slab floor is shown as uninsulated, but it might be.

 

 

 

 

1. Excerpt from the 2021 ASHRAE Handbook of Fundamentals.

The ‘n-Year Return Period Values of Extreme Temperature’ is taken from the ASHRAE Handbook of Fundamentals, 2021, Chapter 14 Climatic Design Information. Section 1, Climatic Design Condition, Applicability and Characteristics of Design Conditions. Recommend using the 5-year value of extreme dry-bulb temperatures. These values can be found in ASHRAE’s Weather Data Viewer for weather stations around the world. https://www.ashrae.org/technical-resources/bookstore/weather-data-center

 

See excerpt from the chapter and the page from the link on the following pages

 

 

 

 

 

 

Proposed Change to Amendment:

1. Add new footnote ‘ac’ language
2. Where an Integrated Heat Pump Water Heater is installed and does not have a ducted intake and exhaust, if the volume of the space containing the water heater is not verified to be at least 450 cubic feet or greater, the maximum allowable UEF shall be 2.0 unless the space containing the water heater is verified to have a total net free opening area of no less than 250 in2, using grilles, louvers, door undercuts, or a louvered door.

 

1. Heat Pump Water Heaters

 

1. Conditioned air. Integrated HPWH (iHPWH and iHPWH_Hybrid) utilizing conditioned air shall comply with the provisions of this section. Design heating loads for the space where integrated HPWH is located shall be equal to or greater than the BTU/hour heat rate of the integrated HPWH. Where installed in an enclosed space with inadequate heat rate, the design heating loads for the adjacent conditioned space shall be equal to or greater than the BTU/hour heat rate of the integrated HPWH, and one of the following requirements have not been met, backup resistance heating is required and the maximum allowable UEF shall be 2.0.

 

1. Passive ventilation shall be provided that is not less than 75 square inches of net free area per 100 watts of compressor, fan, and control power, or the minimum total net free area as determined by the manufacturer, whichever is greater, inclusive of all integrated HPWH installed in the enclosed space.
   1. The enclosed space shall be connected to the adjacent conditioned space using fully louvered doors or two openings of equal area, one located within 12 inches from the enclosure top and one located within 12 inches from the enclosure bottom. It is permissible to combine louvered doors and openings to meet the net free area.
   2. The intake air shall come from, and the exhaust air shall be discharged to the same conditioned space.

 

1. Ducted ventilation shall be provided. Ducts shall be sized to provide not less than 60 cfm per 100 watts of compressor, fan, and control power, or the minimum duct diameter as determined by the manufacturer, whichever is greater, inclusive of all integrated HPWH installed in the enclosed space.
   1. The intake air shall come from, and the exhaust air shall be discharged to conditioned space, with the same pressure zone. Where duct termination points are close together, they shall be directed away from each other.
   2. It is permissible to duct both the intake and exhaust air, or to use passive ventilation for either the intake or the exhaust; the passive ventilation shall be not less than 37.5 square inches of net free area per 100 watts of compressor, fan, and control power or the minimum total net free area as determined by the manufacturer whichever is greater, inclusive of all integrated HPWH installed in the space.
   3. It is permissible to use a transfer fan or inline fan to assist the fan included in the integrated HPWH.

 

1. Unconditioned air. HPWH utilizing outdoor or unconditioned air shall be installed in accordance with one of the following requirements. Where the compressor cutout temperature is above the ‘n-Year Return Period Values of Extreme Temperature’ where n=5 years from the 2021 ASHRAE Handbook of Fundamentals for the nearest applicable climate station, backup resistance heating is required and the maximum allowable UEF shall be 2.0.

 

1. Integrated HPWH (iHPWH and iHPWH_Hybrid), air-source HPWH split (HPWH_S) and air-source HPWH decoupled (HPWH_D) shall be provided with direct access to unconditioned air and installed in accordance with manufacturer’s instructions.
2. Where installed in an enclosed space that has only indirect access to unconditioned air, these HPWH shall meet one of the following requirements.

 

1. Passive ventilation shall be provided that is not less than 75 square inches of net free area per 100 watts of compressor, fan, and control power, or the minimum total net free area as determined by the manufacturer, whichever is greater, inclusive of all integrated HPWH installed in the enclosed space.
   1. The enclosed space shall be connected to the adjacent unconditioned space using fully louvered doors or two openings of equal area, one located within 12 inches from the enclosure top and one located within 12 inches from the enclosure bottom. It is permissible to combine louvered doors and openings to meet the net free area.
   2. The intake air shall come from, and the exhaust air shall be discharged to the same unconditioned space.

 

1. Ducted ventilation shall be provided. Ducts shall be sized to provide not less than 60 cfm per 100 watts of compressor, fan, and control power, or the minimum duct diameter as determined by the manufacturer, whichever is greater, inclusive of all integrated HPWH installed in the enclosed space.
   1. The intake air shall come from, and the exhaust air shall be discharged to unconditioned space with the same pressure zone. Where duct termination points are close together, they shall be directed away from each other.
   2. It is permissible to duct both the intake and exhaust air, or to use passive ventilation for either the intake or the exhaust; the passive ventilation shall be not less than 37.5 square inches of net free area per 100 watts of compressor, fan, and control power or the minimum total net free area as determined by the manufacturer whichever is greater, inclusive of all integrated HPWH installed in the space.
   3. It is permissible to use a transfer fan or inline fan to assist the fan included in the integrated HPWH.
   4. Ducts shall be insulated to not less than R-6.

Entry Date: June 17, 2024 at 6:54 PM

Full Name: Shilpa Surana

Affiliation: 2050 Partners on behalf of California Investor Owned Utilities

Address: 81 Coral Drive Orlinda, California 94563

Phone Number: 5039544711

Email: shilpasurana@2050partners.com

Page Number: 31

Section/Table/Figure Number: footnote ac for service water heating in Table 4.2.2(1)

Comment Intent: Objection

Comment Type: Technical

Comment:

The proposed code change modifies the footnote ac to address the following concerns:

1. Footnote ac requires that the space containing the iHPWH be verified to be 450 cubic feet or greater or total net free area of 250 square inches is met through grilles, louvers, door under cuts or louvered doors. The PG&E Lab testing for HPWH[1] suggests that for single-family new construction, the HPWH should be located in a space of at least 700 cubic feet that will keep the room at the operating temperature range of the heat pump (not cooler than the 50F) for maximizing efficiency. The PG&E lab testing report also recommends a minimum of 150 square inches of NFA for both high and low grilles or a full louvered door, a total of 300 square inches for a 4kBtuh HPWH. Additionally following installation requirements shall be met to maximize airflow.
2. 1. Single layer of fixed flat louvers must be used as the double-slatted louvers impede airflow.
   2. The permanent openings shall be a fully louvered door or two openings of equal size to meet the minimum airflow requirements.

 

[1] Larson, Ben., Larson, Sam. & Gantley, Maya, June, 2023. Laboratory testing of Residential Heat Pump Water Heaters. Impact of Airflow and Space Conkfiguration. PG&E Code Readiness Program Data Brief, Page 55. available at https://www.etcc-ca.com/reports/code-readiness-data-brief-laboratory-testing-residential-heat-pump-water-heater-performance

2. The proposed code change introduces requirements for the following unique installation scenarios.

1. 1. When iHPWH is installed in an enclosed space
   2. When iHPWH is connected to an adjacent space or outdoors
   3. Where iHPWH is connected to an adjacent space or outdoors through a single ducted intake air or exhaust and a permanent opening or louvered door
   4. Where iHPWH is connected to an adjacent space or outdoors through intake and exhaust ducts

 

3. Where the iHPWH is connected to an adjacent space through ducts or permanent openings, it shall connect to the same space, or where outdoor air is used, it shall connect to the outdoors. The intent is to ensure that the ducts do not cross the pressure boundary, which may result in a backdraft causing indoor air quality issues.

 

4. The proposed code change to footnote ac also addresses the requirements when iHPWH is utilizing unconditioned air. The maximum allowable UEF shall be 2.0 unless intended for cold climate installations where the compressor cutout temperature is below the ‘n-Year Return Period Values of Extreme Temperature’ where n=5 years from the 2021 ASHRAE Handbook of Fundamentals for the nearest applicable climate station, Chapter 14 Climate Design Information. These values can be found in ASHRAE’s Weather Data Viewer for weather stations around the world at link belowat link below at https://www.ashrae.org/technical-resources/bookstore/weather-data-center

 

1. iHPWH in basements or unvented attics utilizing outdoor air or unconditioned air have been exempted as the typical operating temperature range of the room will not be cooler than 50F
2. Warmer IECC Climate Zones 1-3 have also been exempted such that the water heater is not penalized for the majority of the hours it will operate in a heat pump mode.

 

Proposed Change to Amendment:

ac.1 Where an Integrated Heat Pump Water Heater (iHPWH) is installed, and does not have a ducted intake and exhaust, if the volume of the space containing the water heater is not verified to be at least 450 cubic feet or greater, the maximum allowable UEF shall be 2.0 unless the space containing the water heater is verified to have a total net free opening area of no less than 250 in2, using grilles, louvers, door undercuts, or a louvered door. the installation meets one of the following:

 

1. Where the iHPWP is installed in a space with no permanent opening, louvered door, or ducts that communicate to an adjacent space or outdoors, the volume of space is verified to be not less than 700 cubic feet.
2. Where permanent openings or louvered doors are used to provide a communicating opening to an adjacent space or outdoors, the following shall be met.
   1. Where indoor air is used, the combined volume of the space containing the iHPWH and the adjacent space is verified to be not less than 700 cubic feet and permanent openings shall connect to the same space.
   2. The total net free area of the permanent openings or louvered door is verified to be not less than 300 square inches.
   3. Where permanent openings are used they shall be of equal area, and not begin less than 12 inches from the ceiling and not less than 12 inches from the floor.
   4. Louvers shall not be double-slatted fixed flat louvers.
3. Where a single ducted intake or exhaust and a single permanent opening or louvered doors are used to provide a communicating opening to an adjacent space or outdoors, the following shall be met:
   1. Where indoor air is used, the combined volume of the space containing the iHPWH and the adjacent space is verified to be not less than 700 cubic feet, and the duct and permanent opening or louvered door shall connect to the same space.
   2. The total net free area of the permanent opening or louvered door is verified to be not less than 150 square inches
   3. Louvers shall not be double-slatted fixed flat louvers.
   4. The airflow from the duct shall be diverted away from the permanent opening or louvered door.
4. Where both the inlet and outlet are ducted, the following shall be met:
5. 1. Where indoor air is used, the volume of the space where the ducts terminate is verified to be not less than 700 cubic feet and the ducts shall connect to the same space.
   2. The airflow from termination points shall be diverted away from each other.

 

ac.2 Where an iHPWH is utilizing outdoor or unconditioned air that is not from a basement or an unvented attic, the maximum allowable UEF shall be 2.0 unless the compressor cutout temperature is below the ‘5-Year Return Period Values of Extreme Temperature’ from the 2021 ASHRAE Handbook of Fundamentals for the nearest applicable climate section.

Exception: Where iHPWH is utilizing outdoor or unconditioned air in IECC Climate Zones 1 through 3.