laboratory assessment of ecoruno co2 air-to-water heat pump · 2017. 9. 29. · refrigeration cycle...

Laboratory Assessment of EcoRuno CO2 Air-to-Water Heat Pump

22 September 2017

A Report of BPA Technology Innovation Project #302

Prepared for

Ken Eklund, Project Principal Investigator Washington State University Energy Program

Under Contract to Bonneville Power Administration

Janice Peterson, Project Manager

Prepared by Ben Larson and Michael Logsdon

Ecotope, Inc.

ii Laboratory Assessment of EcoRuno CO2 Air-to-Water Heat Pump

A Technology Innovation Project Report The study described in the following report was funded by the Washington State University Energy Program under contract to Bonneville Power Administration (BPA) to provide an assessment of the state of technology development and the potential for emerging technologies to increase the efficiency of electricity use. BPA is undertaking a multi-year effort to identify, assess, and develop emerging technologies with significant potential for contributing to efficient use of electric power resources in the Northwest. Neither Ecotope, WSU, nor BPA endorse specific products or manufacturers. Any mention of a particular product or manufacturer should not be construed as an implied endorsement. The information, statements, representations, graphs, and data presented in these reports are provided as a public service. For more reports and background on BPA’s efforts to “fill the pipeline” with emerging, energy-efficient technologies, visit Energy Efficiency’s Emerging Technology (E3T) website at http://www.bpa.gov/energy/n/emerging_technology/. Ben Larson is a principal and director of research at Ecotope. He has a multifaceted background in physics, alternative energy, climate change, and energy efficiency. Among his work at Ecotope is a key role maintaining and developing the SEEM energy simulation program, which is used to model energy efficiency improvements in the residential sector. Mr. Larson also manages projects at Ecotope including Pacific Northwest regional efforts to investigate heat pump water heater performance. Michael Logsdon is a statistician and research scientist at Ecotope. He has a meandering background in engineering, biotech, and mathematics. Mr. Logsdon generates web dashboards for datasets, proposes novel methodologies for analyzing measured energy use, and generally helps people understand their data.

Acknowledgements Ecotope acknowledges Kumar Banerjee, Robert Sant, and Tu Bui of Cascade Engineering Inc, in Redmond, WA for the timely and excellent work in conducting the lab testing. We also thank John Miles of Sanden International for support and technical assistance. Additionally, Ecotope thanks Ken Eklund at WSU for being the conceptual and driving force behind the project.

Abstract Under Technology Innovation Project 338 funded by Bonneville Power Administration (BPA) and the Northwest Energy Efficiency Alliance (NEEA), the Washington State University Energy Program (WSU) contracted with Ecotope, Inc. and Cascade Engineering Services Inc. to assess the ability of the of the Sanden International EDS-C110A EcoRuno heat pump to provide space and water heating. Building on previous work, this project set out to explore the feasibility of using the EcoRuno heat pump in the tested configurations as much as to measure system efficiency. Being a product completely new to the US market, we wanted to see if it was suitable for installations in houses in the proposed configurations and further, how we might improve on the system setup. The project also sought to measure power consumption, output capacity, and efficiency in space heating only mode, in water heating only mode, and in a combined space and water heating scenario.

http://www.bpa.gov/energy/n/emerging_technology/

Laboratory Assessment of Eco Runo CO2 Air-to-Water Heat Pump iii

Glossary of Acronyms and Abbreviations A amps

ASHRAE American Society of Heating, Refrigeration, and Air Conditioning Engineers

BPA Bonneville Power Administration

Btu British thermal unit

C Celsius

CO2 carbon dioxide

COP coefficient of performance

DAQ data acquisition system

DHW Domestic hot water

DOE Department of Energy

EF Energy Factor

F Fahrenheit

GAU Sanden model 80 gallon heat pump water heater

GPM gallons per minute

GPD gallons per day

HPWH Heat Pump Water Heater

Hz hertz

kW kilowatt

kWh kilowatt hours

NEEA Northwest Energy Efficiency Alliance

PNW Pacific Northwest

RH relative humidity

V volts

WSU Washington State University

iv Laboratory Assessment of EcoRuno CO2 Air-to-Water Heat Pump

Table of Contents

Glossary of Acronyms and Abbreviations.................................................................................................................. iii Table of Contents ...................................................................................................................................................... iv Table of Figures .......................................................................................................................................................... v Table of Tables ........................................................................................................................................................... v Executive Summary ....................................................................................................................................................6 1 Introduction .......................................................................................................................................................8

1.1 Sanden EcoRuno Heat Pump ................................................................................................................8 1.2 System Design and Operation ................................................................................................................9 1.2.1 Additional System Components ...................................................................................................... 11

2 Methods ......................................................................................................................................................... 14 2.1 Test plan .............................................................................................................................................. 14 2.1.1 Space Heat Only Tests .................................................................................................................... 14 2.1.2 Water Heat Only Tests .................................................................................................................... 14 2.1.3 Combination Tests ........................................................................................................................... 15 2.2 Lab Testing Setup ................................................................................................................................ 16 2.2.1 Measurement System Layout .......................................................................................................... 18 2.2.2 Measurement Equipment and Specifications .................................................................................. 20

3 Findings ......................................................................................................................................................... 21 3.1 Overall Findings ................................................................................................................................... 21 3.1.1 Space Heating Output ..................................................................................................................... 21 3.1.2 Water Heating Output ...................................................................................................................... 22 3.1.3 Operational Testing Challenges ...................................................................................................... 22 3.1.4 Overall Summary Results ................................................................................................................ 23 3.2 Space Heating Only Tests ................................................................................................................... 24 3.3 Water Heating Only Tests .................................................................................................................... 25 3.3.1 Indirect Tank Tests .......................................................................................................................... 25 3.3.2 Side Arm Heat Exchanger Tests ..................................................................................................... 26 3.4 Space and Water Heating Combined .................................................................................................. 26

4 Conclusions ................................................................................................................................................... 28 References .............................................................................................................................................................. 29 Appendix A: Lab Test Protocol .............................................................................................................................. 30

Laboratory Assessment of Eco Runo CO2 Air-to-Water Heat Pump v

Table of Figures

Figure 1. Basic Schematic for Configuration 1 – Indirect Water Heating ................................................................ 10 Figure 2. Basic Schematic for Configuration 2 – Side Arm Water Heating ............................................................. 11 Figure 3. Air Handler................................................................................................................................................ 12 Figure 4. Indirect Hot Water Storage Tank .............................................................................................................. 13 Figure 5. Side Arm Heat Exchanger ........................................................................................................................ 13 Figure 5. Space Heating Demand Profile ............................................................................................................... 14 Figure 6. Water Heating Demand Profile................................................................................................................ 15 Figure 6. Combined Space and Water Heating Demand Profile ............................................................................ 15 Figure 8. Sanden EcoRuno Installed Inside Thermal Chamber .............................................................................. 16 Figure 9. Hot Water Tank Instrumented and Installed Adjacent to Thermal Chamber ........................................... 17 Figure 11. Air Handler During Installation................................................................................................................ 17 Figure 12. Test Configuration Measurement Points ................................................................................................ 19 Figure 13. Air Handler Supply Thermocouple Grid ................................................................................................. 20 Figure 14. Air Handler Outlet Temperature Measures ............................................................................................ 21 Figure 15. Side arm Water Heating ......................................................................................................................... 22 Figure 16. EcoRuno "Idle" Period Operation ........................................................................................................... 23 Figure 17. Space Heating Only 35F & 47F Compared ............................................................................................ 24 Figure 18. Space Heating Only Output Capacity and Input Power ......................................................................... 25 Figure 19. Water Heating Only at 67F with Indirect Tank ....................................................................................... 26 Figure 20. Space + Water Heating at 17F ............................................................................................................... 27

Table of Tables

Table 1. Basic Equipment Characteristics ..................................................................................................................9 Table 2. Overall Summary Measurements .............................................................................................................. 24

6 Laboratory Assessment of EcoRuno CO2 Air-to-Water Heat Pump

Executive Summary Under Technology Innovation Project 338 funded by Bonneville Power Administration (BPA) and the Northwest Energy Efficiency Alliance (NEEA), the Washington State University Energy Program (WSU) contracted with Ecotope, Inc. and Cascade Engineering Services Inc. to assess the ability of the of the Sanden International EDS-C110A EcoRuno heat pump to provide space and water heating. The project built on several previous assessments of a related product from Sanden, the GAU-315EQTA heat pump (Larson 2013, Larson 2015, Larson 2016). Both use CO2 as their refrigerant. This report conducts a similar assessment for the EcoRuno which has larger output capacity then the previously examined equipment and is built specifically to provide space heating. This project set out to explore the feasibility of using the EcoRuno heat pump in the tested configurations as much as to measure system efficiency. Being a product completely new to the US market, we wanted to see if it was suitable for installations in houses in the proposed configurations and further, how we might improve on the system setup. The project also sought to measure power consumption, output capacity, and efficiency in space heating only mode, in water heating only mode, and in a combined space and water heating scenario. Equipment Under Test The heat plant for the project is the Sanden EDS-C110A EcoRuno heat pump. The heat pump uses a transcritical CO2 refrigeration cycle to extract heat from the ambient air and transfer it to a working fluid – typically water. Unlike previously studied Sanden equipment, this one does not come standard with a tank. Instead, the working fluid can be circulated directly to a space heat system or indirect hot water tank. The product is designed so that the air-to-refrigerant and refrigerant-to-water heat exchange both take place in a single unit using a series of two refrigerant cycles. The equipment compressors, fan, and pump are all variable speed allowing the heat pump to optimize operation and achieve a target output water temperature ranging from ~100F-158F (user settable). The EcoRuno is currently built and sold in overseas markets. It is designed to be paired with space heating distribution systems of the user’s choice. These always have some hydronic component and therefore can be radiators, radiant floors, or fan coils. The space and water heating system selected for this project was a hydronic coil in a central air handler and a hot water tank. Further, two methods of heating water in the tank were examined: an indirect coil immersed in the tank and a “side arm” heat exchanger. The EcoRuno has an integrated pump and, in this set up, it circulates fluid in a primary loop to a Taco all-in-one hydraulic separator and two zone pump module. From this integrated circulator, there are two secondary zones: one for water heating and the other for space heating. In this primary/secondary loop configuration there is direct fluid transfer through the circulation module. The hydraulic separator acts to balance flow between all three loops but the same fluid passes through all three. Testing Plan With direction from Ecotope, Cascade Engineering Services carried out all the lab testing. To do so, they constructed a simulated space and water heating load in the lab with the same components that will be used to install the systems in the field. The test plan called for work in three areas: measuring space heating only performance, measuring water heating only performance, and measuring combined space and water heating performance. The space heating only tests and the combined space and water heating tests were conducted at four ambient air conditions, 5F, 17F, 35F, and 47F under a simulated load. The water heating only tests were conducted at three ambient air conditions, 35F, 67F, and 95F. Further, two water heating scenarios were explored: one with an indirect tank and one with a “side arm” heat exchanger outboard of the tank. The loads were designed to simulate a heating requirement of approximately 30kWh/day and water heating requirement of 8.5 kWh/day (about 46 gallons).

Laboratory Assessment of EcoRuno CO2 Air-to-Water Heat Pump 7

Findings The first part of lab work was in the basic system configuration level as shown in Figure 1 in the following section. Ecotope established an operating regime to optimize output capacity. First, the EcoRuno primary loop pump speed was set so outlet water was 158F (70C). Next, the space heating secondary loop was set at 1.6 GPM and the air handler flow rate at 830 ft

3/min. These settings netted a 25 degree F temperature rise providing heating

supply air from 85F to 95F. The water heating secondary loop flow was set to 1.8 GPM which allowed the 135+F water to flow to the indirect heat tank and easily reach a setpoint of 128F. The observed output capacities for the system configuration tested are as follows.

Space Heating:

o 27,500 Btu/hr at 47F and 35F

o 25,000 Btu/hr at 17F


Water Heating with Indirect Tank Configuration

o 17,500 Btu/hr at 95F and 67F


Water Heating with Side Arm Heat Exchanger

o Inconclusive due to mismatch between EcoRuno operation and thermosiphon design

Input powers of 3,800W (±200W) for space heating and ~2,500W for water heating were observed. Notably, despite having a variable speed compressor, the system did not change input power appreciably over the range of ambient air conditions as seen with the previous Sanden equipment examined. It is conceivable that other system configurations may yield different capacities because the EcoRuno operation appears coupled to the full system. In other words, optimizations of the water-to-air heat exchanger in the air handler, the water tank, or even the pumping regime, may allow the EcoRuno to operate at different output levels. Another important general finding is that the EcoRuno takes approximately thirty minutes to ramp up to near steady-state output from being off. Input power and output gradually increase over this period until a maximum output in steady-state operation is achieved. This is significant because other forced air systems generally reach high output levels within minutes of being turned on. This would indicate a delay in supplying warm air to the house. For a detailed view of the project, all laboratory testing data have been uploaded to an interactive dashboard at the following web address: https://ecotope.shinyapps.io/Sanden_EcoRuno_Lab/. The custom analysis tool – written with the statistical software R and RStudio add-ons – allows one to view a selection of measured and/or derived variables for one or more tests. The test results can be viewed graphically or numerically.

https://ecotope.shinyapps.io/Sanden_EcoRuno_Lab/


1 Introduction Using a single device to provide both the space and water heating needs of a dwelling is a concept with historic roots. Wood burning stoves, used to heat a house, were often used in conjunction with a kettle on top to heat water.

1 More recent wood stoves offer a “side arm” addition for more integrated water heating.

2 Modern

applications of combined space and water heating have most commonly been implemented with natural gas-fired devices. The Center for Energy and Environment has conducted extensive research on how to optimize gas-fired combination systems performance (Schoenbauer 2012, 2014a, 2014b). Recent work conducted by Ecotope and Washington State University explored the feasibility of using an air-to-water heat pump, with electricity as the energy source, to provide space and water heating demands (Larson 2016). This report conducts a similar assessment for the EcoRuno which has larger output capacity then the previously examined equipment and is built specifically to provide space heating. Under Technology Innovation Project 338 funded by Bonneville Power Administration (BPA) and the Northwest Energy Efficiency Alliance (NEEA), the Washington State University Energy Program (WSU) contracted with Ecotope, Inc. and Cascade Engineering Services Inc. to assess the ability of the of the Sanden International EDS-C110A EcoRuno heat pump to provide space and water heating. The project built on several previous assessments of a related product from Sanden, the GAU-315EQTA heat pump (Larson 2013, Larson 2015, Larson 2016). Both use CO2 as their refrigerant. This project set out to explore the feasibility of using the EcoRuno heat pump in the tested configurations as much as it was designed to measure system efficiency. Being a product completely new to the US market, we wanted to see if it was suitable for installations in houses in the proposed configurations and further, how we might improve on the system setup. The project also sought to measure power consumption, output capacity, and efficiency in space heating only mode, in water heating only mode, and in a combined space and water heating scenario. With direction from Ecotope, Cascade Engineering Services carried out all the lab testing. To do so, they constructed a simulated space and water heating load in the lab with the same components used to install the systems in the field. A table describing all tests performed for this report is included in Appendix A: Lab Test Protocol.

1.1 Sanden EcoRuno Heat Pump

The heat plant for the project is the Sanden EDS-C110A EcoRuno heat pump. The heat pump uses a transcritical CO2 refrigeration cycle to extract heat from the ambient air and transfer it to a working fluid – typically water. Unlike previously studied Sanden equipment, this one does not come standard with a tank. Instead, the working fluid can be circulated directly to a heat system or indirect hot water tank. The product is designed so that the air-to-refrigerant and refrigerant-to-water heat exchange both take place in a single unit using a series of two refrigerant cycles. The equipment compressors, fan, and pump are all variable speed allowing the heat pump to optimize operation and achieve a target output water temperature ranging from ~100F-158F (user settable). The EcoRuno is currently built and sold in overseas markets. It is designed to be paired with space heating distribution systems of the user’s choice. These always have some hydronic component and therefore can be radiators, radiant floors, or fan coils. The electrical connections accept standard power input, single phase 220V, 30A, at 50Hz or 60Hz. Table 1 presents salient, basic equipment characteristics.

1 For an example, see http://www.morsona.com/morsoe-7110

2 See http://kitchenqueenstoves.com/

http://www.morsona.com/morsoe-7110http://kitchenqueenstoves.com/


Table 1. Basic Equipment Characteristics

Component EDS-C110A

Height x Width x Depth (mm) 1280 x 828 x 283

Weight (kg) 98

Refrigerant R-744 (CO2)

Resistance Elements None

Heat Pump Input* (kW) up to 4

Output Capacity† (kW) 8.2

*Includes compressor, circulation pump, and fan. Range depends on water and ambient temperature. †

In the configurations tested

1.2 System Design and Operation

The space and water heating system selected for this project was a hydronic coil in a central air handler and a hot water tank. Further, two methods of heating water in the tank were examined: an indirect coil immersed in the tank and a side arm heat exchanger. As described previously the EcoRuno itself is an air-to-water heat pump that makes hot water so it is possible to imagine other heat distribution systems than the ones tested. Figure 1 and Figure 2 present the basic system layout for both configurations tested. The EcoRuno has an integrated pump that circulates fluid in a primary loop to a Taco all-in-one hydraulic separator and two zone pump module. From this integrated circulator there are two secondary zones, one for water heating and the other for space heating. In this primary/secondary loop configuration there is direct fluid transfer through the circulation module. The hydraulic separator acts to balance flow between all three loops but the same fluid passes through all three. None of this water is potable. It is separated from any potable lines by double-wall heat exchangers. In colder climates, it may be desirable to include some glycol in the working fluid as a form of freeze protection. A Taco SR502-4 switching relay nominally orchestrates the entire system. Whenever there is a space heating call, the switching relay engages the EcoRuno, the space heat loop pump within the circulation module, and the air handler fan, all in sequence. Similarly, when there is a call for water heating, the switching relay engages the EcoRuno, and the water heat loop pump within the circulation module. Further, the design guidelines from Sanden recommend prioritizing hot water heating. The switching relay therefore is configured so that when it receives a signal for water heating from the aquastat on the DHW tank, it turns on the EcoRuno and the hot water loop pump while preventing the space heat pump operation. Likewise, when it receives a signal for space heating from the thermostat, it will engage the pump on the space heating loop if it is not currently heating the water tank. The first water heating test configuration (Figure 1), we used a water heater with an “indirect” heat exchange coil inside the tank. Hot water circulates through this coil to warm the tank. The second water heating test configuration (Figure 2), used an external, side arm heat exchanger. Hot water circulates through this side arm from top to bottom which induces a thermosiphon on the tank side of the heat exchanger. This thermosiphon ejects hot water from the top of the side arm to the top of the tank and draws in cold water from the bottom. Both configurations are controlled in the same way via the aquastat which turns on the heat pump (if not already on for heating) and switches on a relay to divert water to the domestic water heater. The only differences are the heat exchange method and the motor and control needed to circulate water through the exchanger in the indirect tank. For the space heating portion, hot water is circulated through a water-to-air heat exchanger. The air handler fan moves air across the coil to heat the space.


Figure 1. Basic Schematic for Configuration 1 – Indirect Water Heating


Figure 2. Basic Schematic for Configuration 2 – Side Arm Water Heating

1.2.1 Additional System Components

To complete the balance of system, several more components were critical to the project including the air handler and water-to-air heat exchanger, circulation pumps, hot water tank, and side arm heat exchanger.

1.2.1.1 Air Handler and Heat Exchange Coil

The air handler and water-to-air heat exchange coil were provided by AirScape3. Figure 3 presents the air

handler. It is variable speed with 10 total steps and an approximate airflow range of 300-1,200 ft3/min. Not

depicted in Figure 3, is the four-row coil which sits in between the filter section and air handler section.

3 http://airscapefans.com/products/Shop/Indoor-Air-Quality/Makeup-Air-Fans/AirScape-CF-Cabinet-Fan-with-Filtration

http://airscapefans.com/products/Shop/Indoor-Air-Quality/Makeup-Air-Fans/AirScape-CF-Cabinet-Fan-with-Filtration


Figure 3. Air Handler

1.2.1.2 Circulation Pumps

The circulation pumps were contained in a single module of two pumps and a hydronic separator. A prototype product from Taco, each pump was fully adjustable and variable speed to allow us to alter heat flow rates.

1.2.1.3 Hot Water Tank

The indirect hot water storage tank was a Heat-Flo HF-80-HO. The heat exchanger, immersed in the tank near the bottom is shown in Figure 4. The HF-80-HO is an 80 gallon tank with all ports, water and working fluid piping, on the top.


Figure 4. Indirect Hot Water Storage Tank

1.2.1.4 Side Arm Heat Exchanger

The side arm heat exchanger is from Alternative Heating & Supplies4. It is 34” long (see Figure 5). Made of

stainless steel, the internal pipe has finned tubing which facilitates heat transfer between the hot water and the working fluid.

Figure 5. Side Arm Heat Exchanger

4 https://altheatsupply.com/side arm-heat-exchanger-34.html

https://altheatsupply.com/side-arm-heat-exchanger-34.html


2 Methods In order to determine the viability and performance of the EcoRuno for combined space and water heating applications, Ecotope, in conjunction with the project advisory committee, drafted a lab test plan.

2.1 Test plan

Ecotope considered using ASHRAE Standard 206 (ASHRAE 2013)as the method of test but opted for a more customized and focused test plan. The procedure to comply with Standard 206 was too lengthy and costly for the budgeted project. More practically, the overall project had more pressing concerns to address about how to maximize system output capacity and efficiency. The scope of Standard 206 is for rating equipment while our questions had more to do with the balance of system design and determining appropriate applications. Previous work on the Sanden GAU product followed a similar approach (Larson 2016). The test plan placed work in three areas: measuring space heating only performance, measuring water heating only performance, and measuring combined space and water heating performance.

2.1.1 Space Heat Only Tests

The test objectives were to first optimize water circulator and air handler flow rates to maximize heat transfer efficiency and then to measure output capacity and efficiency at four different ambient air conditions: 5F, 17F, 35F, and 47F. By iterating through numerous flows, Ecotope set the heating loop circulator flow rate at 1.6 GPM and the air handler flow rate at 830 ft

3/min. These were arrived at to supply outlet air at 90F or above – a

generally accepted minimum supply temperature for central forced air heating. These rates are widely adjustable and so could be varied to suit a particular installation configuration or even theoretically be varied by a central controller to optimize for performance. Figure 5 shows the space heating demand profile used for all tests. It consisted of three heating calls over the course of eighteen hours. The first heating call of thirty minutes started the test. The second, lasting three hours, occured between 3 hours 45 minutes and 6 hours 45 minutes. The third, and final, heating call began at hour eleven and lasted 1.5 hours. The total heating time ran five hours. The tests run on an 18 hour cycle to allow the lab personnel to reset the equipment during normal working hours and run the tests overnight.

Figure 5. Space Heating Demand Profile

2.1.2 Water Heat Only Tests

Similar to the space heat only tests, the first objective was to maximize heat transfer into the hot water tank by adjusting circulator flow rates. The next objective was to measure performance at three ambient air conditions: 35F, 67.5F, and 95F. The test plan called for conducting these tests with both the indirect tank and the side arm. Given the heating rate and outlet temperature of the EcoRuno, Ecotope found that 1.8 GPM circulating through the indirect tank was a reasonable flow rate to use to heat the tank to 128°F. The hot water draw profile was 46 gallons per day derived from a 3-person household as observed in PNW field studies (Ecotope 2015). The average occupancy house, of 2.7 people, uses 42 gallons, supplied from a tank with a 128°F setpoint, so this is only slightly more. Figure 6 displays the draw profile on the same time scale as the space heating profile.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

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Figure 6. Water Heating Demand Profile

2.1.3 Combination Tests

The combination tests were designed to layer the domestic water heating demand on top of the space heating demand. As described previously, priority was given to the domestic water heating so that when the tank needed to be heated, flow was diverted from space heating. Therefore, there was no simultaneous space and water heating. Rather, they were always staggered. In essence, the combination tests increased the load on the system for the test duration. Figure 6 shows both loads on the same graph.

Figure 6. Combined Space and Water Heating Demand Profile

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2.2 Lab Testing Setup

Ecotope collaborated with Cascade Engineering, WSU, and NEEA to devise methods and protocols suitable for carrying out the testing plan. The general approach and methodological overview for this test are provided here. The outdoor unit was placed in a thermal chamber where the ambient air conditions are tightly regulated (Figure 8). The hot water tank was placed next to the chamber in the large lab space (Figure 9). That lab space is kept thermally controlled by a space heating thermostat. The temperature varied from 60°F to 70°F. The small changes in temperature led to slight changes in the heat loss through the tank but the impacts on the overall system efficiency measurements were minimal. The air handler was located in another chamber near both the outdoor unit and the water tank (Figure 11). Ultimately the thermal conditioning capabilities of this chamber were not used because intake air temperatures, coming from the lab were approximately steady at 65F. The hot supply air from the air handler was ducted away from the air handler and above the acoustic tile to a cavernous plenum above the lab. This successfully avoided any local increases in air temperature.

Figure 8. Sanden EcoRuno Installed Inside Thermal Chamber


Figure 9. Hot Water Tank Instrumented and Installed Adjacent to Thermal Chamber

Figure 11. Air Handler During Installation


2.2.1 Measurement System Layout


Figure 12 presents the detailed measurement points for both water heater testing configurations. They are all listed below providing a key to the figure.

Power/Energy Measurements

o P1 – EcoRuno Heat Pump o P2 – Air Handler o P3 – Integrated Circulation Module

Water Flow o FM1 – Primary Loop o FM2 – Zone 2, Air Handler o FM3 – Zone 1, Water Heater o FM4 – Domestic Hot Water (DHW) Usage o FM5 – Side arm (expect low flow rates)

Temperature o T1 & RH1 – Main thermal chamber temperature and relative humidity o T2 – Primary Loop Return Water Temperature o T3 – Primary Loop Supply Water Temperature o T4 – Zone 2 (Fan Coil) Return Water Temperature o T5 – Zone 2 (Fan Coil) Supply Water Temperature o T6 – Zone 1 (DHW) Return Water Temperature o T7 – Zone 1 (DHW) Supply Water Temperature o T8 – Secondary Thermal Chamber Air Temperature (Fan Coil Return Air Temperature) o T9 –DHW Inlet Temperature o T10 – DHW Outlet Temperature o T11 – Lab Air Temperature o T12 – Side arm Entering Water Temperature o T13 – Side arm Exiting Water Temperature o Thermocouple Tree – typical design with 6 thermocouples evenly spaced o Thermocouple Grid – 2-dimensional grid of thermocouples (3x3) in air handler supply air stream


Figure 12. Test Configuration Measurement Points


2.2.2 Measurement Equipment and Specifications

In accordance with Figure 12, Cascade Engineering installed an instrumentation package to measure the required points. All instrumentation was calibrated and has accuracies well within those specified by the Department of Energy for water heater and heat pump testing. Cascade Engineering measured inlet and outlet water temperatures with thermocouples immersed in the supply and outlet lines. Three thermocouples mounted to the surface of the evaporator coil at the refrigerant inlet, outlet, and midpoint monitored the coil temperature to indicate the potential for frosting conditions. Power for the EcoRuno was monitored for the entire unit including the compressor, fan, and pump all at once. Similarly, power for the circulation module was monitored as a whole unit. For the DHW flow events, Cascade Engineering conditioned and stored tempered water in a large tank to be supplied to the water heater at the desired inlet temperature. A pump and a series of flow control valves in the inlet and outlet water piping controlled the water flow rate. A flow meter measured and reported the actual water flow. The data acquisition (DAQ) system collected all the measurements at five-second intervals and logged them to a file. In a post processing step, Ecotope merged the temperature log of the thermal chamber with the DAQ log file to create a complete dataset for analysis. For the space heating measurements, Cascade Engineering installed nine thermocouples in a grid across the outlet of the air handler to accurately measure supply air temperature. Figure 13 shows the grid without the outlet ducting attached. Both Ecotope and Cascade Engineering conducted a one-time characterization of air handler flow using flow plates. Pressure, flow rates, and fan motor power consumption were mapped at all operating speeds and with the duct attached exactly as it was during other tests. Return air temperature was measured just upstream of the air intake. Combined, the temperature rise and air flow rate through the air handler provided a measurement of heating capacity.

Figure 13. Air Handler Supply Thermocouple Grid


3 Findings

To begin, all laboratory testing data have been uploaded to an interactive dashboard at the following web address: https://ecotope.shinyapps.io/Sanden_EcoRuno_Lab/. The custom analysis tool – written with the statistical software R and RStudio add-ons – allows one to view a selection of measured and/or derived variables for one or more tests. The test results can be viewed graphically or numerically. The findings section of this report contains a selection of curated views from the web dashboard.

3.1 Overall Findings

3.1.1 Space Heating Output

Under the system configuration tested, the measurements showed a space heating output capacity largely invariant with outside air temperature. The observed outputs ranged from 27,500 Btu/hr at 47F and 35F down to 25,000 and 23,000 at 17F and 5F respectively. Despite possessing a variable speed compressor, the input power was remarkably stable over the temperature range with a typical power draw of 3,800W (±200W). With the space heat circulator flow rate set at 1.6 GPM and the air handler fan at 830 ft

3/min, the warm air supply

air measured 85-95F with return air ranging from 60-70F. Notably, at the beginning of a heating cycle, the outlet air temperature was lower as the EcoRuno ramped up its output. This typically took 30 minutes before the heat pump achieved a near steady-state output. Figure 14 shows the measured air temperature for the nine thermocouple grid at the air handler outlet. The data show remarkable uniformity in temperature readings across locations. The supply air temperature was taken as an average of all nine measurements.

Figure 14. Air Handler Outlet Temperature Measures

https://ecotope.shinyapps.io/Sanden_EcoRuno_Lab/


3.1.2 Water Heating Output

For the indirect tank testing configuration, the EcoRuno showed a maximum water heating output capacity of 17,500 Btu/hr at both 67F and 95F ambient air. Input power was approximately 2,500W. Curiously, most of the way through each of these tank recovery cycles, the EcoRuno stepped down power and output dramatically. This appears to have occurred with all but the bottom sixth of the tank near setpoint. This also coincided with a drop in EcoRuno outlet water temperature as if the system were trying to optimize operation. For the 35F ambient air test, this second operating regime was not observed. At 35F, the output capacity was diminished slightly to a maximum of 15,000 Btu/hr. Like in the space heating only scenarios, the EcoRuno took approximately 30 minutes of continuous operation to ramp up to near steady-state behavior. The testing of the side arm water heating configuration provided valuable insight in to its operation. With a cold tank of water, the thermosiphon was operating at its strongest but was only able to heat the tank at a peak rate of 3,500 Btu/hr. Most interesting, that heating capacity, or viewed from the point of the primary loop, heat extraction rate, was too low for the EcoRuno to run continuously. In a matter of minutes, the primary loop would achieve temperatures in excess of 150F which caused the EcoRuno to switch off. This is likely by design – the refrigeration cycles were not designed to operate with heat discharge rates this low. Figure 15 illustrates the situation. The side arm heat exchanger took in 50F water from the tank and provided a 60F-70F temperature rise. The thermosiphon was working but only to a degree. The flow rate from the tank through the side arm heat exchanger was too low to transfer heat at a meaningful rate. The system operated in this way for 16 hours before we aborted the test. Before the end, the top half of the tank nearly attained set point.

Figure 15. Side arm Water Heating

3.1.3 Operational Testing Challenges

Assembling all of the disparate components for the project – for a system never before built – proved challenging. In the end, all components were identified and acquired except for a special connector to a control point on the EcoRuno which, due to logistical constraints, was not available at the time of system testing. The connector would allow a direct signal to be sent to the EcoRuno to turn it on or off. Ideally, this would be synchronized with a call for space or water heating and originate from the switching relay. In lieu of that connection, the testing proceeded with the EcoRuno on continuously. This meant that while neither the space nor water heating secondary loop circulators were on, the EcoRuno ran its own pump, on the primary loop, at approximately 4.75 GPM. During these “idle” periods, without any need to provide space or water heating, the temperature of the


water in the primary loop would fall so that every 45 minutes, the EcoRuno compressor system would momentarily run to reheat the primary loop. The primary loop lines were insulated but the temperature dropped anyway as the water passed between the EcoRuno and the integrated circulation module. Figure 16 shows the operation during a typical four hour “idle” period. Shortly after 7.5 hours in to the test, the primary loop temperature had dropped to 115F which caused the EcoRuno to run at 1500W for ten minutes while also dropping its primary pump flow rate to 1.6 GPM. That quickly reheated the small amount of water in the loop to 150F, at which point, the heat pump shut off. Of note, the EcoRuno’s monitoring of the primary loop water temperature and its drop to ~115F is the trigger for the heat pump to turn on. Without direct control of the equipment, this is exactly how the EcoRuno decided to turn on when there was a real need for space or water heating. In those cases, the secondary loops – the space and water heating loops – placed a larger and longer heating load on the primary loop so that the EcoRuno ran longer.

Figure 16. EcoRuno "Idle" Period Operation

The system operation, without direct control over the heat pump, was neither ideal nor what would be expected of an installation in a real house. To accommodate this, all subsequent summary analyses were conducted by excluding the energy use of the EcoRuno during the idle periods.

3.1.4 Overall Summary Results

Table 2 shows the overall, summary measurements for all tests conducted. As discussed in section 3.1.3, the reported EcoRuno energy consumption is that under the idealized state where it is controlled to have no idle period runtime. Further the reported energy consumption for the total system includes the air handler and the circulation pumps whenever they operate. For both the space heat and water heat only tests, the table shows the expected, general trend of increasing COP with increasing ambient air temperatures. A closer look at the summary data reveals comparisons across test groups are challenged due to myriad behavioral differences of the EcoRuno between tests. Both findings within a test group and between them are discussed in the following sections. For reference, the air handler used 120W, the space heating loop pump 34W, and the hot water loop pump 11W.


Table 2. Overall Summary Measurements

Test Type

Test Conditions

Space Heat Added (kWh)

Domestic Water Heat Added (kWh)

Input Energy - Total System (kWh)

Equipment COP

Space Heat Only

5F Air 29.6 0 17.8 1.66

17F Air 33.2 0 18.3 1.82

35F Air 29.7 0 14.9 2.00

47F Air, Repeat 34.8 0 16.6 2.10

Water Heat Only

Indirect Tank, 35F Air 0 8.50 4.89 1.74



Sidearm, 35F Air 0 6.94 12.3 0.56

Combined Space + Water Heat

5F Air 22.9 8.13 20.1 1.54

17F Air 25.4 8.49 18.8 1.80

35F Air 22.2 8.44 15.9 1.92

47F Air 23.3 8.41 16.6 1.91

3.2 Space Heating Only Tests

The four space heating only tests, consisted of three heating events over an eighteen hour period and produced COPs from 1.7 at 5F to 2.1 at 47F ambient air. The tests were setup so that the heating periods always occurred at the same time and for the same duration regardless of outdoor temperature. The idea was to guarantee a heating load and ease comparisons. Instead, it somewhat complicated the comparisons because although there was a heating load, the system was not set up to maintain a fixed temperature in a given space. This meant that the total heat output could vary from test to test if the EcoRuno engaged in a defrost cycle or similarly changed its output capacity (note there is no direct, external control of the heat pump output capacity). Figure 17 shows space heating tests at 47F (dashed line) and 35F (solid line). The 35F undergoes a frosting event at hour 5 and a subsequent defrost at hour 5.25. During this period, the output is significantly reduced. There is another defrost event at hour 6.5 and then the need for heating ends shortly before hour 7.

Figure 17. Space Heating Only 35F & 47F Compared


There were no frosting events observed for the other three temperature conditions. The air was either too warm or too dry. Still, the equipment operated at slightly different input powers and output capacities at all ambient temperatures despite having the same heating loop flow rate and similar heating load. Figure 18 presents all four tests over the course of the entire heating periods. Differences in input power and output capacity between the ambient air test conditions are challenging to discern in the graph because they were all very slight with the exception of the 35F test which shows the dip at hour 5.5. In these tests, the EcoRuno had essentially the same response across all ambient temperatures.

Figure 18. Space Heating Only Output Capacity and Input Power

3.3 Water Heating Only Tests

3.3.1 Indirect Tank Tests

As mentioned previously, the indirect tank tests showed interesting behavior from the EcoRuno. For the majority of the hot water tank reheating cycle, the EcoRuno operated in a high output mode. As the tank approached setpoint, the water warmed, and the EcoRuno dropped in to a lower output state to finish heating the tank. Figure 19 shows the full test, with two reheating cycles for the 67F ambient air condition. The bottom graph shows the temperature profile within the tank, the middle, the flow rates, and the top, the output capacity. For these tests, the tank aquastat, located one-third from the bottom, was set at 128F with a deadband of ~20 degrees F. In all cases, the system was able to provide the hot water required of the 46 gallon draw pattern albeit with low efficiencies for heat pump water heaters.


Figure 19. Water Heating Only at 67F with Indirect Tank

3.3.2 Side Arm Heat Exchanger Tests

Described in the overall findings section, the side arm heating configuration was not able to function with the test setup in the lab. There is a mismatch between the amount of heat transferred to the water tank and the amount provided by the EcoRuno. Either a more vigorous thermosiphon is needed to increase heat transfer or the EcoRuno output needs to be limited for this pairing to work. Preferably, the side arm heat exchange rate would be increased because the observed heating rate of 3,500 Btu/hr is not acceptable by normal hot water usage standards. One possibility is to increase the flow rate through the heat exchanger with a pump instead of relying on the passive thermosiphon. Another possibility is to use a pump with a plate and frame heat exchanger which may have more surface area for heat transfer than the side arm model tested. Because this setup was not successfully operated, no subsequent tests or investigations were conducted.

3.4 Space and Water Heating Combined

Figure 20 displays how the system operated with combined space and water heating. Per the plan, the test began with a call for space heating for thirty minutes. Shortly after hour 3.5, the normal call for space heating began but was interrupted after only minutes of operation by an overriding call for water heating. The water tank dropped far enough in temperature to need to be reheated and, since water heating was given priority at the switching relay, the space heating circulator and air handler shut down. The water heating proceeded for the next hour. Only when that was completed, did the space heating continue. Due to the experimental design, this cut into the space heating runtime and effectively reduced total space heating output for the entire experiment. That pattern repeated itself for all combination tests which is why the space heating output in Table 2 is lower for the combination tests than for the stand alone versions. An interesting side effect of the combination tests is that the EcoRuno was often running to provide space or water heat when the other end use was needed. This has the benefit of eliminating the ramp up period. The heat pump was already on and operating at full output so it could provide full capacity immediately. Curiously, even though operating at steady-state is usually beneficial for performance, it does not look as if this increased the overall system COP.


Figure 20. Space + Water Heating at 17F


4 Conclusions

This project succeeded in demonstrating a combined space and water heating system with a novel, air-to-water heat pump, the EcoRuno. Space heating was supplied by an air handler with a hydronic coil producing 23,000-27,500 Btu/hr of heat depending on ambient air conditions. Two water heating methods were investigated. The first, an indirect tank, showed a heating rate of 17,500 Btu/hr (~5kW) and handily brought the hot water tank up to setpoint at 128F each time it was needed. The second, a side arm heat exchanger was shown not to be successful with the operational controls tested. The heat transferred through the side arm appeared too small to induce the EcoRuno to run continuously. If the heat exchange rate in to the tank could be increased or the EcoRuno output decreased, this configuration appears to have an opportunity of working. The Taco integrated circulation module proved extremely flexible and easy to configure. This was useful not only in the testing environment but the ability to continuously set flow rates to different zones will enable a variety of install configurations in the field. Likewise, the variable speed settings on the air handler were easy to work with and enabled optimization of output capacity and supply air temperature. The EcoRuno itself proved to be a capable, yet complex machine. It produced water in excess of 160F with outdoor temperatures of only 5F. This happened in response to varying end use loads and load profiles. The equipment operation was nevertheless complex. The overall output capacity seemed coupled to the balance of system components (the air handler and water heating setup). It is highly likely changing those for different components will alter the EcoRuno operation but it is unclear how (higher or lower output or efficiency). Unlike a simple gas boiler, the EcoRuno clearly has sophisticated, internal logic, to control operation to achieve certain heat discharge rates but, again, it is unclear what those are and how to best design a system around them. As an example, the heat pump takes approximately thirty minutes to ramp up from being off to full output. Any practical installation should take that and other findings in this report in to consideration.


References

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Appendix A: Lab Test Protocol