Mitsubishi Heavy Industries Technical Review Vol. 48 No. 4 (December 2011)76

Development of the “Q-Ton” CO2-Refrigerant
Heat Pump for Industrial Water-Heater Systemsofor Use at Outside Air Temperatures Down to -25 C

Air-Conditioning & Refrigeration
S ystems Headquarters

Traditionally, water and room heaters have mainly been powered by oil and gas burners. This
trend is currently shifting toward heat-pump systems to achieve reduced carbon dioxide (CO2)emissions which are thought to be a cause of global warming. In particular, heat pump water-heatersystems with CO2-refrigerant, which have a global warming potential (GWP) of 1, are already inwide domestic use in mild-climate areas, and are also seeing increased industrial use, owing to theirability to furnish a high-temperature water supply by exploiting their refrigerant characteristics.
In cold-climate areas, the reduced heating power and energy efficiency at low outside airtemperatures leads to increased initial and operating costs, due to the increased number ofinstallations required. This results in slow prevailing speeds for industrial systems in thecold-climate Hokkaido and Tohoku areas. Mitsubishi Heavy Industries, Ltd. (MHI), has developed
an industrial water heater based on the “Q-ton ESA30” CO2-refrigerant heat pump (hereinafterreferred to as “Q-ton”), with a heating capacity of 30 kW, to solve these problems and contribute to
the reduction of CO2 emission. The new system adopts an innovative two-stage scroll-rotary (GSR)
compressor for significantly improved heating capacity at cold outside air temperatures.

|1. Features(1)

The world’s first two-stage GSR compressor“Q-ton” adopts the newly developed two-stage GSR compressor, which exhibitssignificantly improved performance at cold outside air temperatures. The GSR compressor isshown in Figure 1. It has two compression stages. The low stage has a rotary compressor
mechanism that provides good compression efficiency at low-pressure ratios, while the highstage has a scroll compressor that provides good compression efficiency at high-pressure ratios.
The inside of the housing is designed for medium pressure. This configuration offers thefollowing advantages. The two-stage compression reduces the leak-loss during the compression
stroke, and provides high compression efficiency. Refrigerant gas injection into themedium-pressure housing between the two compression stages enables increased refrigerant
recirculation on the heating side (gas cooler), and increases the heating capacity.
(2) Refrigeration cycle based on gas injection into the GSR compressor at medium pressures
Figure 2 shows a refrigeration cycle using the GSR compressor. The two-stagecompression allows the use of optimum medium pressure and control of the quantity of gas
injected. The refrigerant is separated into liquid and gas after expansion, under optimum
medium-pressure conditions, and gas-cooler refrigerant recirculation and heating capacity are
increased in comparison to a single-stage compression cycle with direct gas inhalation into thecompressor. The decreased amount of recirculated liquid refrigerant that flows into thevaporizer reduces the electric consumption in the compressor and increases the energy
efficiency.

Mitsubishi Heavy Industries Technical Review Vol. 48 No.4 (December 2011)
77

Figure 1(3)

Two-stage GSR compressor

Figure 2

Refrigerant cycle – Mollier diagram

Heating capacity and energy-saving characteristics of “Q-ton” compatible with low outside
air temperatures
The heating capacity and energy efficiency (COP: coefficient of performance or heating
power electricity consumption) of “Q-ton” are compared to those of other manufactured
systems at various outside air temperatures in Figures 3 and 4.
Figure 3 shows the heating capacity at various outside air temperatures. The heating
capacity in moderate seasons is assumed to be 100%. The heating capacity rate is the heating
capacity at various outside air temperatures compared to the capacity at a moderatetemperature. Inverter driven water heaters from other manufacturers exhibit capacityodeterioration at an outside air temperature of 0 C, while “Q-ton” retains its full heating capacity
oat outside air temperatures down to -7 C. The other heaters exhibit capacity degradation ofo70% or less at an outside air temperature of -15 C, whereas “Q-ton” retains a capacity of 70%
oor more at outside air temperatures down to -20 C.

Figure 3 Heating capacity relative to outside
air temperature

Figure 4 Energy efficiency relative to outside
air temperatures

Figure 4 shows the COP variation with respect to the outside air temperature. All of theheaters have reduced COP at lower temperatures. “Q-ton” has the smallest COP reductiono(COP = 2.27) at an outside air temperature of -25 C. Heaters from other manufacturers have
COP values of 2.0 or less, while the COP of “Q-ton” is 38% higher. Assuming a 33%
electricity generation efficiency at the terminal, this translates into a primary energy conversion
efficiency of approximately 92%, which is better than that of a boiler.
Field tests were conducted using the new system as a substitute heater for a boiler inthree cold-climate areas (Hokkaido, Iwate, and Toyama), beginning in December, 2010. The
heating capacity, energy-saving performance, and reliability in a cold climate (including
anti-freezing measures used for water pipes and drain water, defrosting and snow-removal of
the outside heat exchanger, and the range of the refrigeration cycle and electrical equipmentoperation) were verified.
The reductions in operating cost and CO2 emissions are listed in Table 1.

Mitsubishi Heavy Industries Technical Review Vol. 48 No.4 (December 2011)
78Table 1ColdclimateareaPremises

Field tests

Operating cost CO2 emissions
DataConven(compared to a (compared to ational acquisition
conventional
conventionalperiodfuelsystem)

system)

50%

65%

43%

59%

54%

53%

Dec. 2010
Kitchen,Hokkaido
Fuel oiltorestroom
Jan.2011
FactoryJan. 2011
Iwate
health Kerosene
tofacility
March2011
Jan. 2011
BoilerToyama feed-water Fuel oil
toFeb.2011
heatingFigure 5
Touch-panel
remote controller

The electricity fees were calculated from the power consumption at each site, and the fuelcosts were calculated from the conversion of heating energy to the conventional boilers. The
electricity consumption includes the energy consumed by the anti-freezing heater for the water
pipes in the system. The operating costs were reduced to 43% to 54%, and CO2 emissions to53% to 63%, compared to the existing heater. Since we were able to observe improvement inrunning cost and CO2 emissions in colder seasons, it is expected to result in a much higher COP
during moderate and summer seasons when the outside air temperature is higher. Therefore, theoperating costs and CO2 emissions are expected to be reduced to approximately one third of
those of the current system over a whole year.
oIn Hokkaido, the outside air temperature is occasionally below -20 C. It was verified that aohot water temperature of 90 C (as a planned heating capacity) can be readily obtained under these
conditions via heat pump operation.
(4) Touch-panel remote controller allows finely adjusted operation for energy savings
In an industrial water heater based on a CO2-refrigerant heat pump, for improved
energy-saving performance, it is necessary to control the heat source to achieve heat-storage
operation compatible with onsite hot water requirements. The main remote controller (Figure 5)
provides a peak-cut timer, a weekly timer, a setting function for stored hot water temperatures,a transition chart showing stored hot water quantities, and an on-screen user manual based on
customer requirements. Also, a single remote controller can control a unit with a heating
capacity of 30 kW and up to 16 coupled units (a total of 480 kW) for better operability.
(5) Unvented or open vent tank selection according to customer requirements
Unvented or open vent tanks can be applied per customer request, and for easy
replacement of existing heaters. The heat source unit is compatible with both tanks, facilitatingwide market applicability.

|2. Specifications
Table 2 lists the “Q-ton” specifications.
Table 2

“Q-ton” specifications

Specification
Moderate season heating capacity*
Outside air temp.
16DB/12WBoo
Water in at 17 C, out at 65 C
Winter season heating capacity*
Outside air temp.
7DB/6WBoo
Water in at 9 C, out at 65 C
Dimensions
WeightRefrigerant

Heating capacity
Electricity consumption
COP
Heating capacity
Electricity consumption
COP
H×W×D

“Q-ton” ESA30
kWkW－kWkW－mmkg

30
6.98
4.330
8.0
3.75
1,690×1,350×720
365
Ｒ744(CO2)
oOutside airC-25 to 43oOperating temperature range
Water inletC
5 to 63
oWater outlet
C60 to 90* The measuring conditions for heating capacity, electricity consumption, and COP were compliant withJRA4060 of the Japan Refrigeration and Air Conditioning Industry Association performance for industrial
heat-pump water heaters