07 Hearing Exhibit 108_Attachment JTS-4_RMH_Heat Pump_Study.pdf

Technical Feasibility of

Applying Air and Water

Source Heat Pumps to

Steam Customer

Segments

December 22 2023

Prepared By:

TITLE

DATE

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4 Proceeding No. 22A-0382ST

TABLE OF CONTENTS

Executive Summary

Technical Feasibility

Construction and Operating Costs

Greenhouse Gas Emissions Reductions

Customer Segmentation Methodology

Background and rationale for segmentation:

Rationale for segments used

Segmentation results:

Technology Descriptions

General Assumptions:

Air Source Systems:

Segment #1: Heating water

Segment #2: Condenser Water

Segment #3: Steam Direct Converted to VRF

Production of Domestic Hot Water Under All Segments

Water Source Systems:

Segment #1: Heating water

Segment #2: Condenser Water

Segment #3: Steam Direct Converted to VRF

Production of Domestic Hot Water Under All Segments

Review Of Ultimate Heat Source for Water Source Systems

Ground Source Potential

District Ambient System Potential

Summary Load Profile Information

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4

Overview of Profiles

Air Source Profiles

Water Source Profiles

Electrical Demand Implications

Opinions of Probable Capital and Operating Costs

Construction Costs

Operating Costs

Feasibility Study Considerations

Future Cost Growth

Emissions and Decarbonization impacts - Energy

Emissions and Decarbonization impacts – Refrigerant leakage

Timeline Assumptions for Adoption of Alternative Technologies

Implications of Energize Denver

Summary and Recommendations

Summary of Key Findings

Recommendations

Suggested Next Steps

EXECUTIVE SUMMARY

This study considers the feasibility of using building-level air and water source heat pump technology to replace the heating energy currently supplied by the Public Service Company of Colorado’s district steam system. Detailed information about the heating, ventilating, and air conditioning (HVAC) systems of each customer building was developed in a previous phase of this study and was used for this investigation.

The findings are summarized in the graphics below.

Figure 1.1 Infographic Showing Results of Feasibility Analysis for Air Source Heat Pumps

Figure 1.2 Infographic Showing Results of Feasibility Analysis for Water Source Heat Pumps

TECHNICAL FEASIBILITY

Air source heat pump (ASHP) systems are currently feasible for customer buildings, but the only systems capable of operating in Denver’s climate are variable refrigerant flow (VRF) systems. These systems require a complete replacement of the current HVAC systems installed in the buildings served by the steam system. Air to water heat pumps would be ideal to serve the existing HVAC systems in most customer buildings, but most air to water heat pumps will not operate below 0°F. Based on conversations with equipment suppliers, this situation is expected to improve in the near future. Much of the information developed in this report assumes performance based on expectations of that future equipment. Utilizing ASHPs also requires a significant quantity of equipment to be mounted outside the buildings. Space, noise, and aesthetic concerns will need to be managed in locating new air source equipment.

Water source heat pump systems are currently feasible for customer buildings. Systems can be designed and installed that interface with the existing building HVAC systems of most steam customers. Systems connected to a district energy system, such as an ambient loop, are likely to provide the best economic performance of the heat pump conversion options considered. The heat sources and sinks, design details and costs for an ambient loop are not considered in this report. Some possible configurations of ambient loop piping arrangements are described in a companion report.

The viability of ground source systems was investigated and found to be technically feasible for only a few of the buildings connected to the district steam systems. The buildings for which ground source

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4 would be economically feasible are even fewer. This is mostly due to a lack of available site area upon which to drill and install a wellfield for the ground source system. There are developing and unproven drilling techniques that might increase the number of buildings where ground source could be technically feasible, but the difficulties of drilling in the tight urban conditions downtown will continue to limit economic feasibility.

CONSTRUCTION AND OPERATING COSTS

An opinion of the construction cost to convert buildings to heat pump systems, as well as the anticipated utility costs pre- and post-conversion, are presented. The construction cost for either air or water source conversion is considerable. That cost would be partially offset by savings in utility costs, but these savings are not substantial enough to make project economics a primary driver of the conversions. It is anticipated that government policies and other incentives will be needed to drive implementation of heat pumps in these buildings.

The table below shows the costs and savings for all steam customers combined to convert to an air or water source system:

System Type Construction Cost Annual Customer Cost

Savings

Air Source Systems $365 Million1 $10 Million

Water Source Systems $600 Million1 $10 Million2

1. Electrical infrastructure and ambient loop construction costs not included)

2. Includes ambient loop service costs

GREENHOUSE GAS EMISSIONS REDUCTIONS

Switching to air or water source heat pumps (WSHPs) would result in significant reductions in greenhouse gas emissions. The reductions would be immediate and increase over time as electrical power supply becomes less carbon intensive. The annual savings with assumed 2030 emissions factors are equal to 53,500 metric tons. This is equivalent to the emissions of almost 12,000 gasoline powered passenger vehicles, or 1% of Denver’s total building emissions in 2021.

• ASHP emissions reductions using 2022 emissions factors = 37%

• ASHP emissions reductions using 2030 emissions factors = 70%

• WSHP emissions reductions using 2022 emissions factors = 47%

• WSHP emissions reductions using 2030 emissions factors = 75%

Additional considerations that could impact heat pump conversions, such as future costs, decarbonization impacts, and the requirements of Energize Denver are also presented in the Feasibility

Study Considerations section.

CUSTOMER SEGMENTATION METHODOLOGY

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4

This section describes why and how steam customers were divided into customer segments for further analysis. During the previous study, steam customer information about each building and how the steam delivered by the district system is used was gathered. This process revealed that every building has its own unique character, and any modifications to its heating systems will need to be a unique engineered solution. The previous study restricted its scope to changes addressing only the energy source, allowing standard blocks of equipment to be applied to each building. That approach made it clear that to apply heat pumps more significant modifications to buildings are required, including renovations, energy savings measures, and retrofit solutions throughout the building. This is a much more complex undertaking, making a building-by-building approach impractical for the scope of this study. Instead, steam customers are segmented into several groups. General solutions for each type are developed and per-building costs are developed using those solutions in concert with size and complexity factors.

BACKGROUND AND RATIONALE FOR SEGMENTATION:

The district steam system has been operating for over 120 years and has accepted new customers throughout its life span. In that time, the design and construction of building heating systems has evolved through many different system types. Building envelope design and materials have similarly changed over time. The steam system serves buildings with a wide variety of sizes and uses.

In order to divide the steam system’s customers into segments with similar solutions, we considered all possible heat pump HVAC systems and then looked at what features of buildings would make each system more or less applicable to that building. To do this, we evaluated 11 features that might impact which type of heat pump heating solution we would apply to a segment and determined that only three had a significant impact. The factors considered are listed below:

• Use type

• Year Built

• Heating System Type

• Heating Fluid Temperature

• Cooling System Type

• Domestic Water Requirements

• Building Size

• Site Area

• Peak Heating Load

• Annual Energy Use Intensity

• Other Special Circumstances

The three factors in bold are the ones that were used to determine building segmentation. A short summary of the reasoning behind including or not including each factor is given in the following paragraphs.

Use Type: If a building is used as an office, a performing arts theater, a condominium, or a data center.

Use type results in different types of spaces, which in turn lead to different HVAC solutions. An office typically consists of many small zones with modest ventilation requirements. A performing arts theater will have large volume spaces with high ventilation requirements.

Year Built: Although there is some correlation between heating system type, envelope performance, and the age of a building, these were not strong correlations, and we determined that it would be best to focus on these factors directly and to not focus on the age of a building.

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4

Heating System Type: The heating types used in the buildings served by the steam system break down into a couple categories. These include buildings still using steam radiators for heating, buildings using heating water systems, and condenser water buildings that already have heat pumps installed but use steam to maintain condenser water temperature. In order to apply a heat pump solution to a steam radiator building the entire heating system would need to be replaced. In a heating water building or a condenser water building a significant portion of the system would be reused. The chart below shows the distribution of heating system types among steam customers.

Figure 2.1 Heating System Type by Steam Use

The heating hot water segment is by far the largest. It is broken down by use type. The Hot Water –

Ventilation segment is comprised of theaters and other assembly spaces. Hot Water – Perimeter is all the buildings with smaller zones and lower ventilation requirements, such as offices, hotels, and retail spaces. The Mix of Hot Water/Steam buildings are buildings with some of both system types. Most of these buildings are predominately hot water with a few steam coils that exist in building air handlers.

Heating Fluid Temperature: This factor applies to heating water buildings. Buildings designed to be heated by water at 140°F or less can use more standard heat pumps, while buildings that require hotter water will require specialized heat pumps or renovation of the building envelope and/or HVAC system to reduce the water temperature to a range that can be attained with standard equipment.

Cooling System Type: We deliberated whether cooling system type would change the preferred heat pump heating solution. Within the information available for this study, there were no buildings where cooling system type would be a determining factor for selection of a heat pump system. Cooling system type did however play a role in determining how many buildings could recover heat internally.

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4

Domestic Water Heating System Type: In many cases, the steam system provides both heating water and domestic hot water. Although, some buildings use steam for building heat while using another means to heat water for handwashing, showers, and cleaning. Even in buildings where domestic water use is significant, such as in hotels, we did not find a reason to change the heat pump solution from what would be best for heating water. Instead, domestic water can usually be addressed as an extension of the heating water system. Where a standalone system is needed, it can be addressed as an adjustment to the overall building solution.

Building Size: The size of a building relates to its peak demand and therefore equipment size. However, we found that most heat pump solutions are scalable. So, once a solution is determined by the use type and fluid temperature, the building size does not change the equipment and systems used—only the size or number of systems that need to be deployed.

Site Area: The area of the site is considered specifically to determine if ground source heat pumps are a viable solution. When building loads and available site area are considered, only a few buildings have technically feasible solutions within their property boundaries. See the section reviewing ground source heat pump potential.

Peak Heating Load: Similar to building size, this was not a determining factor.

Annual Energy Use: The annual energy use of a building has many causes, and it is hard to determine whether the building envelope, the type of HVAC system, or the way the building is operated is the largest contributing factor to the bottom line. That said, this factor was used to look closer at buildings that might benefit from an envelope upgrade. It did not make sense as a factor to determine which heat pump solution would be best for a building.

Other Special Considerations: While reviewing the buildings on the district steam system, we looked for other individual circumstances that should be considered. One consideration was if a building was also on the district chilled water system. As we were tasked with developing an air source and water source solution for each building, this did not change the heat pump solutions being used but did indicate where water source solutions might be more feasible. Another special consideration was that a few buildings use steam for laundry, sterilization, or other process uses. These represent a small fraction of steam use and would not be easily served by a heat pump solution. As a fringe case, no solutions are provided for these special uses within this study.

RATIONALE FOR SEGMENTS USED

Because so many buildings on the steam system have heating water systems, it is important to represent these as a customer segment and develop heat pump solutions for several subsegments within this large segment. The goal is to preserve as much existing HVAC infrastructure as can reasonably be reused while maximizing the efficiency of the heat pump heating system. By preserving infrastructure, conversion costs will be reduced, which will result in better heat pump adoption rates.

Two additional segments encompassed the remaining customers: “steam direct,” buildings that use steam heating systems throughout the building, and “condenser water,” buildings with distributed heat pumps operating on a condenser water loop. Unique solutions were applied to these segments and with little variation between buildings no subsegments were needed. The steam direct segment is referred to

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4 in the remained of the report as “Steam Direct, Convert to VRF” to clearly delineate both the type and the solution, which is to convert the building HVAC system to a variable refrigerant flow (VRF) system.

The considerable number of buildings with mixed steam and heating hot water systems were split between the heating water and steam direct segments. The majority of these buildings only have a few steam coils and mostly use heating water. These were considered heating water buildings. The buildings that did not have enough heating water to be worth reusing were considered steam direct buildings.

SEGMENTATION RESULTS:

The customer segments and subsegments used in the analysis are listed in this section. The pie charts in this section show the percentages each segment represents in terms of peak steam demand and annual steam consumption. The great majority of steam energy is converted to hot water for heating. As discussed in the heating technologies sections, heating water systems present both challenges for the application of heat pumps and opportunities to reuse significant portions of existing systems. A secondary set of pie charts further breaks down the hot water segment by achievable water temperature and by whether building modifications would be required to achieve that water temperature. These subsegments of the large hot water segment have implications for energy use and electrical demand as is explained in subsequent sections of this report.

Figure 3.2 Customer Segmentation by Steam Use

The paragraphs below describe the segments and subsegments with and where buildings from the initial screening were placed.

Segment #1: Heating Water

This segment includes all buildings with heating water distribution and most of the buildings with a mix of steam and heating water.

Segment #1a: 140°F Heating Water Design Achievable

This subsegment includes all buildings whose existing heating water systems operate at 140°F or lower. It also includes buildings where a140°F heating water supply temperature is likely achievable with modifications to the HVAC system or localized envelope improvements (such as better lobby entry doors).

Segment #1b: 140°F Heating Water With Envelope Improvements

This subsegment includes buildings currently operating with water hotter than 140°F but where improvements to the building envelope are expected to reduce the peak water temperature down to 140°F. These are generally buildings with poorer performing envelopes, where window inserts or replacements would greatly improve envelope performance. The reduced heating load could then be met with lower heat output from the existing HVAC system operating at lower water temperatures. See the technology section for more information on envelope improvements.

Segment #1c: 170°F Heating Water (No Cost-Effective Path to 140°F)

Buildings where it is not practical to modify the building or the existing HVAC system to use

140°F heating water are included in this category. Many buildings operate at 180°F currently, and some use water as high as 200°F. In order to use commercially available HVAC-grade heat pump systems, these buildings need to operate at 170°F and may need modifications just to operate at that lower temperature verses higher set point. As is explained in the technology section, operating at 170°F instead of 140°F requires more equipment, reduces efficiency, and increases electrical demand.

Segment #2: Condenser Water

This segment includes buildings using a condenser water loop and existing distributed WSHPs for heating. In these buildings, steam is used to provide heat to the condenser water loop to make up for the heat removed by the heat pumps when the building operation is heating dominant. Solutions for this segment only address replacing the heat the steam provides to the condenser loop; the remaining building systems are not modified.

Segment #3: Steam Direct Converted to VRF

Where steam is used directly to heat a building, the entire system needs to be removed. There are no commercially available heat pumps that can produce steam. A new VRF system will be used to

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4 replace steam heating (as well as the rest of the HVAC system) in these buildings (see the technology section).

TECHNOLOGY DESCRIPTIONS

This section describes the heat pump technology applied to each customer segment. It includes air source systems that can be used without any connection to a district energy system. It also includes water source systems that can be used with a ground source (or geo-exchange) wellfield or a district energy system supplying energy through an ambient temperature fluid. After general assumptions are presented, the technology used to address each building segment for both air and water source options is presented.

GENERAL ASSUMPTIONS:

In selecting the technology to be used for the analysis in this report, two overarching guidelines were followed. The first was to provide a system that would replace the heating energy currently supplied by the steam system via an efficient electric heating system. The second was to choose the most cost-effective solutions available. The next paragraphs look at each guideline in detail.

1. Provide heating energy using an efficient electric heating system

The selected technology could not be electric resistance heating since electric resistance heating was analyzed in the prior phase of this study and the implications for utility and building electrical infrastructure were already determined. The selected central technology was required to be a heat pump system capable of moving heat from a source into the building with an efficiency greater than 100%—in other words, with a coefficient of performance (COP) greater than one. Note that the study did allow the use of small amounts of electric resistance heating within the building at specific zones in order to enable reduction of the building heating water supply design temperature and thereby enable the use of heat pumps (see the details under constraint two below).

Critically, the selected heat pump system was required to be able to operate within the expected temperature ranges for Denver’s climate. The record low temperature in Denver is -29°F, which was measured in 1875. The lowest recent temperature was -24°F, occurring in 2022 (per the National

Weather Service). Many ASHP systems cease to function below a specified outdoor air temperature.

These temperatures range from around 30°F down to -27°F, depending on system type and manufacturer. For this study, electric resistance was also not allowed to be used as “backup” when a heat pump stops functioning at low temperatures because the backup amount of electric resistance heat required would be as large and require as many electrical infrastructure upgrades as the previously studied full electric resistance systems would. For the purposes of this report, systems operating down to

-27°F were considered to be acceptable and peak power requirements were calculated at the low (-

17°F), which occurred during the example year used for the study calculations.

2. Choose the most cost-effective solution

Among other considerations this guideline required the selected technology to be compatible with retaining as much existing building infrastructure as possible. As described in the segmentation section, most of the buildings that are currently served by steam use heating water HVAC systems within the building. To avoid removing and replacing these systems, heating water heat pump solutions are ideal.

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4

Unfortunately, currently available commercial equipment does not produce water as hot as the 180°F that is used in many of the buildings. In addition, currently available air source equipment producing heating water have an outdoor temperature cutoff between 0°F and -4°F, below which the equipment will not operate at all.

In order to resolve this dilemma, the study makes several reasonable assumptions. First, the study assumes that buildings can reduce their heating water temperature to at least 170°F. Other studies and experiments have generally found that this water temperature would still meet comfort requirements in all but a small percentage of zones. A small amount of electric resistance heating was applied for a portion of the heating load at some buildings to ensure that comfort conditions were maintained throughout.

Second, the study assumes that air to water systems will become available with the capacity to extract heat from air down to -22°F. In discussions with equipment manufacturers, this appears likely as manufacturers respond to increased demand for heat pumps in cold climates. There is also no fundamental reason why currently available technology cannot be used to develop new heat pump products that can operate down to that low of an outside air temperature. The heat pumps will still be constrained by thermodynamical laws, and it will likely be necessary to take more than one step between

-22°F and the heating water temperatures used in many buildings. Currently, air to water heat pumps that can operate below 0°F in outside air are rare because they have not been in demand within the

HVAC industry.

Using the assumption that low ambient air to water heat pumps will become available allows buildings to retain their existing heating water infrastructure. Because there is still a building segment where the entire HVAC system is replaced, the results for the “steam direct converted to VRF” segment can be used as comparison for what the results for the hot water segment would look like without the assumption that low ambient heat pumps become available.

While the existing steam system is primarily used for building heating, a significant portion is used for the production of domestic hot water. For buildings that produce heating water, it is relatively simple to produce domestic hot water at the same time. For buildings that do not have heating water, a separate system must be added that produces domestic hot water. Domestic hot water technology is presented at the end of each of the air source and water source sections.

AIR SOURCE SYSTEMS:

General description of the technology:

ASHP systems move heat from one airstream to another fluid (air or water) via a refrigeration cycle. They can be used to provide building heating as well as air conditioning (including both cooling and dehumidification where needed). The performance capabilities and characteristics of a system depend on the pressure and type of refrigerant used, the capabilities of the compressor, and the temperatures of the source air and the second fluid.

The efficiency and capacity of these systems is highest when the “lift,” which is the difference in temperature between the air and the second fluid, is lowest. The heating efficiency and capacity both decline as source air temperatures decrease, while the temperature for indoor comfort remains the

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4 same. See Chart 3.1 below for the efficiency curves used in this report. Additional technical resources on these systems are available from the American Society of Heating, Refrigeration, and Air Conditioning

Engineers and from HVAC equipment manufacturers.

Figure 3.1 Chart Showing Efficiency Curves of Air Source Systems Used in This Report

General Assumptions:

• The systems are sized to provide the same amount of heat as was provided by the steam system at the coincident outdoor temperature (except where heating loads are reduced by envelope improvements).

• The majority of the heating is provided by heat pumps. A maximum of 5% of the peak load is assumed to be electric resistance heating. No natural gas heating systems are used.

• Defrost cycles are accounted for in the overall efficiency numbers. It is assumed that enough individual refrigerant circuits will be provided so defrost cycles can be staged so as to not interrupt heating.

• The existing load profile is not impacted by any changes to ventilation systems. Some changes may be required to comply with building codes when replacing HVAC systems, but these impacts cannot be estimated without more detailed engineering design.

• Available exterior building space is sufficient for the number of ASHPs required.

SEGMENT #1: HEATING WATER

1.00

1.50

2.00

2.50

3.00

3.50

4.00

-20 -10 0 10 20 30 40 50

H e a ti n g C

O P

Outside Air Temperature (°F)

Heating COP vs OA Temperature by Heat Pump Type - Air Source

Heat Pumps

140deg HWS - ASHP

140deg HWS - Cascade ASHP-

WSHP

170deg HWS - Cascade ASHP-

WSHP

VRF ASHP

140deg HWS ASHP - Projected

170deg HWS - Cascade ASHP-

WSHP Projected

140deg HWS - Cascade ASHP-

WSHP Projected

60deg CWS - ASHP

60deg CWS - ASHP - Projected

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4

For this segment, the ASHP systems extract heat from outside air and move it into the building heating water system. This type of system is often called an air to water heat pump. They are commercially available in a variety of sizes and from a variety of manufacturers. There is a major, likely temporary, concern with this technology. Few manufacturers offer a system capable of operating below 0°F. A few manufactures offer high pressure CO2 heat pumps capable of operating below 0°F with high lift, but these are designed for domestic water heating. They require cold inlet water temperature and are not suitable for building heating systems. Only a single manufacturer was found to advertise a heating system capable of operating at lower temperatures, but they could not provide performance data, despite repeated requests, before this report was published.

Heat pumps struggle with lift (difference between outside temperature and inside temperature) greater than 120°F. Creating 140°F to 170°F water from 0°F air or colder with a single heat pump is infeasible. A two-stage heat pump “cascade” system is employed by this study, when temperatures required it, to reach the required heating water supply temperatures. In this system, the first heat pump heats an intermediate water loop to between 60°F and 95°F. The intermediate loop then serves as the heat source for the second-stage water to water heat pump. Because the intermediate loop runs outside to the air source units, an antifreeze solution should be used.

Once heating water is generated by the heat pump at a sufficient temperature it is supplied to the building, and the remainder of the HVAC system will continue to operate just as the system operated with steam as the heat source. No changes are required to the ventilation and cooling systems.

Segment #1a: 140°F Heating Water Design Achievable:

For this segment, an air to water cascade is used to extract heat from the air outside the building and provide heating to the building via heating water at 140°F. When outdoor temperatures are below freezing, the first-stage heat pump produces 60°F water and a second stage draws heat from this water to produce 140°F water. During mild weather a single stage of the heat pump is used to generate 140°F heating water. The diagram in Figure 3.2 shows the system concept, and the chart in

Figure 3.3 plots the efficiency of the system versus outside temperature.

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4

Figure 3.3 Coefficient of Performance Curve for Segment

#1a System

The heating COP chart above has two lines. The red line shows the cascade system, and the blue line shows the ASHP generating 140°F water in a single stage. The cascade is required to operate below

0°F, and below about 32°F it is more efficient than the single-stage heat pump. Above 32°F, the system operates at high efficiency using the single stage. With some piping, valves, and controls, the system for this segment can operate via whichever set of equipment has the highest efficiency at any given time based on the outside temperature.

The existing building electrical system must be modified to serve the new heat pumps. This will be an additional load on the electrical system using additional energy. In most buildings this will result in a higher peak electrical demand in the winter than the existing summer demand.

Segment #1b: 140°F Heating Water With Envelope Improvements:

This segment is identical to segment #1a in terms of the heat pump technology employed. The improvement of the exterior envelope required to bring buildings of this segment to a point where 140°F water is sufficient to heat the building requires its own technology. Although there are several technologies, materials, and techniques capable of improving the thermal performance of the envelope, it is often difficult to quantify cost and effectiveness without a detailed design. For this reason, the study models the use of window inserts.

Figure 3.2 System Diagram for Segment #1a

Figure 3.4 Window Insert Technology Diagram

2.00

2.50

3.00

3.50

4.00

-20 0 20 40

H e a ti n g C

O P

Outside Air Temperature (°F)

Heating COP vs OA Temperature 140°

HWS -Cascade ASHP-WSHP

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4

The window insert is installed on the inside face of the existing windows and improves envelope performance by increasing insulation at the windows and by decreasing infiltration through window openings. The manufacturer of this product was able to provide example data that could be used to quantify envelope performance for this study. Figure 3.4 above, from Alpen High Performance

Products (a Colorado-based producer of window inserts), shows how the insert increases thermal performance. While this may not be the only solution, it is a cost-effective one that was relatively simple to apply for the purposes of this study.

Segment #1c: 170°F Heating Water (No Cost-Effective Path to 140°F):

For this segment, an air to water cascade system is used to extract heat from the air outside the building and provide heating to the building via heating water at 170°F. The first-stage heat pump produces 95°F water, and a second stage draws heat from this water to produce 170°F water.

During mild weather these temperatures can be relaxed, and it may even be possible to heat with a single stage for improved efficiency. The point at which the system can operate with lower temperatures will be building dependent, this study assumes an outside air temperature where all buildings can operate with a single stage and higher efficiency. The diagram below shows the system concept, and the chart below plots the efficiency of the system versus outside temperature.

The existing building electrical system must be modified to serve the new heat pumps. This will be an additional load on the electrical system using additional energy. In most buildings, this will result in a higher peak electrical demand in the winter than the existing summer demand.

Figure 3.5 System Diagram for Segment #1c

Figure 3.6 Coefficient of Performance Curve for Segment #1c

2.00

2.50

3.00

3.50

4.00

-20 0 20 40

H e a ti n g C

O P

Outside Air Temperature (°F)

Heating COP vs OA Temperature

170° HWS -Cascade ASHP-WSHP

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4

SEGMENT #2: CONDENSER WATER

For this segment, the ASHP systems replace the existing steam heat fed into the building condenser water loops. These loops can operate as low as 40–60°F in the winter, and so only a small lift is required. This is, in effect, a cascade system with the second stage being the existing distributed single zone WSHPs in the building. The lack of equipment capable of operating below 0°F is still a concern. Just because the water side temperature is lower the heat pump does not allow a lower air side temperature.

The compressor operating envelope must still be able to handle the refrigerant pressure and temperature to operate below 0°F. This report uses the projected efficiency of future systems that are expected to be capable of operating below 0°F. The diagrams below illustrate the system arrangement and the efficiency curve.

Figure 3.8 Coefficient of Performance Curve Segment #2

Note that the HVAC system does not change downstream of the point where heat is injected into the condenser water loop. The existing building electrical system must be modified to serve the new ASHPs.

This will be an additional load on the electrical system using additional energy. In most buildings, this will result in a higher peak electrical demand in the winter than the existing summer demand.

Figure 3.7 System Diagram for Segment #2

1.5

2.5

3.5

4.5

-20 0 20 40

H e a ti n g C

O P

Outside Air Temperature (°F)

Heating COP vs OA Temperature

- ASHP for Condenser Water

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4

SEGMENT #3: STEAM DIRECT CONVERTED TO VRF

For this segment, the proposed solution requires that the entire existing heating system is removed, and a new heating and cooling system is installed. Most buildings will have an existing cooling system that will also be demolished and replaced by the new systems. The building’s ventilation system will be evaluated and likely replaced with a new dedicated outdoor air system with a heat recovery device to comply with building codes and to limit heating loads from ventilation air.

The new heat recovery VRF system will consist of one or more banks of outdoor units and many indoor cassettes. Each cassette will supply heating and cooling to one zone within the building. The system will be designed to maximize heat recovery between interior and exterior zones and across different solar exposures of the building. The system will need to be a “cold climate” system rated for continuous heating below 0°F, ideally down to -22°F. The diagrams below illustrate the system arrangement and the efficiency curve.

The existing building electrical system must be modified to power the new VRF system. Most of the new power will go to the outdoor units where the compressor motors are located. However, each indoor zone cassette will also require its own electrical power for the fan and onboard controls. The cassette power demand will be small and will likely be able to use existing nearby electrical panels, but new circuits, conduits, and occasionally new panels will potentially be required. As this system will replace both the existing heating and existing cooling systems, many buildings will be both removing and adding load. The results of the modeling performed as part of this study show that overall electrical demand is still likely to increase because of power requirements for this system at peak heating.

Figure 3.9 System Diagram for Segment #3 Figure 3.10 Coefficient of Performance curve for Segment

#3

2.5

3.5

-20.00 0.00 20.00 40.00

H e a ti n g C

O P

Outside Air Temperature (°F)

Heating COP vs OA Temperature

- VRF System

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4

PRODUCTION OF DOMESTIC HOT WATER UNDER ALL SEGMENTS

While in almost every building the majority of the heat currently delivered by the steam system goes to space heating, many buildings also use steam to produce domestic hot water. Some buildings also have separate domestic water heating systems that do not use the district steam system. For the purposes of this study, domestic hot water energy was quantified by considering steam use during the summer months when no building heating is required and during awake hours. This was assumed to be the rate at which heat is required for domestic hot water year-round.

Domestic water heating was treated differently in each segment. The bullets below detail conceptual systems upon which the calculations in this report are based.

1. Segment #1: Heating Water

In this segment at least 140°F water is produced, and the domestic hot water can be produced by the same systems that produce heating water. In the case of the 170°F cascade, a separate 140°F heat pump operating from the intermediate loop is used to generate domestic hot water.

2. Segment #2: Condenser Water

In this segment, building domestic hot water was found typically to generate directly from the steam system, and so a separate domestic hot water heat pump was required. The new heat pump system operates off the condenser water loop to generate 140°F water for domestic use.

3. Segment #3: Steam Direct Converted to VRF

The new VRF systems cannot produce domestic hot water, and so a separate air to water heat pump system is required to generate domestic hot water. An air to water cascade, similar to those used in segment #1, or a high lift domestic hot water heat pump can be used. This study assumes an air to water cascade generating 140°F domestic water.

WATER SOURCE SYSTEMS:

General description of the technology:

WSHP systems move heat from a water source to another fluid (air or water) via a refrigeration cycle.

They can be used to provide building heating as well as air conditioning (cooling and dehumidification where needed). The performance capabilities and characteristics of a system depend on the refrigerant used, the compression capabilities, and the temperatures of the source water and the second fluid.

The efficiency and capacity of these systems is highest when the lift, which is the difference in temperature between the source water and the second fluid, is lowest. The heating efficiency and capacity do not vary as much as air source systems because the source water temperature is generally more consistent. The efficiency curves shown below assume that the source water only varies 15 degrees (from 55°F down to 40°F) throughout the year. Additional technical resources on these systems are available from the American Society of Heating, Refrigeration, and Air Conditioning Engineers and from HVAC equipment manufacturers.

Figure 3.11 Composite Chart of Water Source System Heating Coefficient of Performance

General Assumptions (same as for ASHP systems):

• The systems are sized to provide the same amount of heat as was provided by the steam system at the lowest anticipated source water temperature (except where heating loads are reduced by envelope improvements).

• The majority of heating is provided by heat pumps. A maximum of 5% of the peak load is assumed to be electric resistance heating. No natural gas heating systems are used.

1.5

2.5

3.5

4.5

-20 -10 0 10 20 30 40 50

H e a ti n g C

O P

Outside Air Temperature (°F)

Heating COP vs OA Temperature by Heat Pump Type - Water

Source Heat Pumps

140deg HWS - WSHP

170deg HWS - Cascade WSHP-

WSHP

VRF WSHP

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4

• The existing load profile is not impacted by any changes to ventilation systems. Some changes may be required to comply with building codes when replacing HVAC systems, but these impacts cannot be estimated without more detailed engineering design.

SEGMENT #1: HEATING WATER

For this segment, the WSHP systems extract heat from water circulated to the building and move it into the building heating water system. The ultimate source of the heat for the water source systems would be a ground source heat exchanger or “ambient loop” district system. Both are discussed in other sections of this report. The performance of the system is similar regardless of the source of heat. The water source temperature is assumed to range from the low 40s to the mid 50s during the heating season. From these temperatures, there are commercially available systems that can generate 140°F heating or a little hotter in a single stage. There are heat pumps that are capable of making hotter water, but the source water must be hotter as well. Therefore, for buildings that need 170°F heating water, a two-stage cascade system is used.

Once heating water is generated by the heat pumps at sufficient temperature it is supplied to the building, and the remainder of the HVAC system will continue to operate just as the existing system did.

No changes are required to the ventilation and cooling systems.

Segment #1a: 140°F Heating Water Design Achievable:

For this segment, a single-stage heat pump is able to supply heating water to the building from the source water. This is well-established technology. Many ground source heat pump buildings use this equipment, and heat pumps capable of operating at these temperatures have been manufactured for decades. The diagram in Figure 3.12 shows the system concept, and the chart in Figure 3.13 plots the efficiency of the system versus outside temperature.

Figure 3.12 System Diagram for Segment #1a

System Figure 3.13 Heating Coefficient of Performance Chart for

Segment #1a System

2.5

3.5

-20 0 20 40

H e a ti n g C

O P

Outside Air Temperature (°F)

Heating COP vs OA Temperature

- 140°F WSHP

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4

Segment #1b: 140°F Heating Water With Envelope Improvements:

This segment is identical to segment #1a in terms of the heat pump technology employed. The technology used in this study to improve the envelope is described in the air source section and copied here for convenience of reference.

The improvement of the exterior envelope required to bring buildings of this segment to a point where 140°F water is sufficient to heat the building requires its own technology. Although there are several technologies, materials, and techniques capable of improving the thermal performance of the envelope, it is often difficult to quantify cost and effectiveness without a detailed design. For this reason, the study models the use of window inserts.

The window insert is installed on the inside face of the existing windows and improves envelope performance by increasing insulation at the windows and decreasing infiltration through window openings. The manufacturer of this product was able to provide example data that could be used to quantify envelope performance for this study. Figure 3.14, above, from Alpen High

Performance Products (a Colorado-based producer of window inserts) shows how the insert increases thermal performance. While this may not be the only solution, it is a cost-effective one that was relatively simple to apply for the purposes of this study.

Figure 3.14 Window Insert Technology Diagram

Segment #1c: 170°F Heating Water (No Cost-Effective Path to 140°F):

For this segment, a water to water cascade is used to extract heat from the water source (either geothermal or ambient loop) and provide heating to the building via heating water at 170°F. The first-stage heat pump produces 115°F water and a second stage boosts this up to 170°F. With a heat pump cascade, the highest efficiency occurs when the efficiency of each heat pump stage is maximized and the efficiency of the two stages are close together (for example, a system with a first-stage COP of 3 and second-stage COP of 3 is more efficient than a system with COPs of 2 and 4, respectively). Water temperatures are selected to maximize the overall efficiency. During mild weather, 170°F water is not required to meet the heating demand. When this is the case, the water temperatures at each stage can be relaxed, or it is possible to heat with a single stage for improved efficiency. The point at which each building can operate at higher efficiency varies by building.

This study assumes a specific outside air temperature where all the buildings operate on a single stage. The diagram above shows the system concept, and the chart plots the efficiency of the system versus outside temperature.

SEGMENT #2: CONDENSER WATER

The water source conversion for this segment is simple. The existing condenser water loop only needs to be tied into the water source loop, either directly or via a flat plate heat exchanger. From there, the existing WSHPs continue to operate as they always have. For this segment, there is no additional equipment needed and no additional electrical power required for building heating. Where buildings in this segment also generate domestic hot water, new equipment and power is needed for that system.

1.0

2.0

2.5

3.0

3.5

4.0

-20 0 20 40

H e a ti n g C

O P

Outside Air Temperature (°F)

Heating COP vs OA

Temperature - 170°F WSHP

Cascade

Figure 3.15 System Diagram for Segment #1c System

Figure 3.16 Heating Coefficient of Performance Chart for Segment #1c System

SEGMENT #3: STEAM DIRECT CONVERTED TO VRF

For this segment, the entire existing heating system is removed and a new heating and cooling system is installed. Most buildings have an existing cooling system that would also be demolished. The building’s ventilation system would be evaluated and likely replaced with a new dedicated outdoor air system with heat recovery to comply with building codes and to limit heating loads from ventilation air.

Figure 3.17 System Diagram for Segment #1c System

A water source VRF system is similar to an air source system but is more efficient, especially at low outside air temperatures. A new water source heat recovery VRF system would consist of one or more sets of central VRF compressor units and many indoor cassettes. Each cassette would supply heating or cooling to one zone within the building. The system would be designed to maximize heat recovery between interior and exterior zones and across different facades of the building. Excess heat would be rejected to the water source loop and when the balance of the system is in heating, heat would be drawn from the water source loop. The diagrams below illustrate the system arrangement and the efficiency curve.

Figure 3.18 Heating Coefficient of Performance Chart for

Segment #1c System

1.0

2.0

2.5

3.0

3.5

4.0

4.5

5.0

-20 0 20 40 H e a ti n g C

O P

Outside Air Temperature (°F)

Heating COP vs OA Temperature -

Water Source VRF

Hearing Exhibit 108, Second Supplemental Direct Testimony of Joseph T. Schwark, Attachment JTS-4

PRODUCTION OF DOMESTIC HOT WATER UNDER ALL SEGMENTS

While in almost every building the majority of the heat currently delivered by the steam system goes to space heating, many buildings also use steam to produce domestic hot water. Some buildings also have separate domestic water heating systems that do not use the district steam system. For the purposes of this study, the domestic hot water energy was quantified by considering the steam use during the summer months when no building heating is required.