The Development of High Temperature Water Heater using CO2 … · 2016-11-23 · The Development of...
Transcript of The Development of High Temperature Water Heater using CO2 … · 2016-11-23 · The Development of...
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The Development of High TemperatureWater Heater using CO2 Heat Pump
1. Introduction2. Refrigerant choice 3. Advantages of CO2 water heater 4. Technological development of major components 5. Steps for the next generation CO2 water heater 6. Conclusion
Contents
April 5, 2008Shigeharu TAIRA, Product Development Group,Air Conditioning Manufacturing Division, DAIKIN Industries, Ltd.
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21.8%
3.4%
21.6%6.4%
46.8%
Lighting, appliances, etc:
Heating
Household direct CO2 emission in Japan2005 (Greenhouse Gas Inventory Office of Japan)
1. Introduction
●Water heating emits more than 20% of residential CO2 emission in Japan.⇒It’s a very important challenge to reduce CO2 emission from this usage. (CO2 emission due to residential energy is about 14% of Japanese total emission)
●Furthermore, more than 90% of water heaters are combustion-type ⇒There is a good chance for heat pump to reduce CO2 emission
●Mid-night power is surplus due to nuclear power plants. Electricity charge is determined according to the demand and the supply correlation. ⇒An efficient thermal storage system utilize mid-night power is ideal!
Background : Problem of Japanese GHG emission situation
Hot water supply:
Cooling
Kitchen Combustion type:90%
Electric type(heater, a heat pump):10%
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●HFC is energy efficient and reasonable cost ⇒Effectiveness of heat pump water heater as a measure against global warming may be diminished by high GWP of HFC.
●Research to utilize CO2 for air conditioning have been under way for more than decade. (in Europe and Japan in particular)⇒For air conditioning, it has not been considered commercially
practical yet.However, CO2 for water heating has potential of equivalent or better performance than HFC
We decided to develop high temperature water heater for thermal storage system with CO2 heat pump. Compressor as well as water heat exchanger are developed to meetthe properties of CO2.
Background : Challenges in refrigerant choice
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Comparison of a refrigerant■ HFC R410A, R407C have considerably higher COP but far higher GWP than CO2.
Even if the heat pump water heater has lower CO2 emission, the effect to reduce global warming impact (against fossil fuel heating systems) would be deteriorated if HFC refrigerant is not fully recovered.
■ CO2 is not suitable for the reversible air source heat pump because of its low theoretical COP especially in cooling operation. But, it has good potential for high temperature heat pump due to trans-critical operation in high pressure side.
HFCsHFCs Natural refrigerantNatural refrigerantCO2R410A R407C A/C High Temp
90
ODP*1 0 0 0
Flammability No No No
Discharge Pressure [MPa] 2.7-3.0 1.8 -2.0 9.5 -11
GWP*2 1975 1652.5 1
Toxicity Low Low Low
COP [relative to 410A] 100 95 -100 60-80
Refrigerant
Note:*1: Ozone depletion potential,*2: Global warming potential(IPCC2001)
2. Refrigerant characteristics
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Refrigerant HFC CO2
Figure ofoutline
Fluorocarbons heat low-temperature water by high condensing temperature.⇒Irreversible loss is unavoidable, so the
theoretical efficiency is low.
Characteristics Fluid in a supercritical condition does not change the phase. The temperature of CO2drops gradually as the heat is transferred. ⇒Loss is smaller!
Comparison of a refrigerant■ CO2 is suitable for water heaters and other once-pass heating applications
with large temperature differences.
2. Refrigerant characteristics
Heat value
Temp.
1-Stage Cycle using typical Fluorocarbon
HFCs
Water
High
Low
HighLow Heat value
Temp.
Trans-Critical Cycle using CO2
CO2
Water
High
Low
HighLow
6DAIKINDAIKIN 3. Advantages of CO2 water heater
■ Cumulative sales targeted at 5.2 million units by 2010Result is lower, but expanded by 50% every year.
CO2 Water heater sales target and result in Japan
CO2 Water Heater sales target (as of 2005) and result (up to 2006)
Compact models
For cold areas
Current models
Cumulative sales: 5.2 mil. Units
Cumulative sales: 5.2 mil. units
For cold areas
Compact models
Current models
(1,000 units)
Year
Aim
sale
s num
ber
0.34 3.72 8.08 13.1 22.6 35.0 Result
1,400
1,200
1,000
800
600
400
200
0
01 02 03 04 05 06 07 08 09 10
5.0 35 80120
230
520
690
950
1,170
1,390
230120
520650 700 710 720
520
160 320
36
160
100
140990(19%)
440(8%)
3,770(73%)
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P
Heat exchanger and fan(common or similar parts with A/C)
Water heat exchanger Compressor
Heat pump unit Hot water storage tank
P
Tank
Bath
System of CO2 water heater & thermal storage■ The CO2 heat pump water heater heats up
water to high temperature at mid-night that is stored in storage tank.
■Appropriate temperature water is supplied by mixing hot stored water and cold water for day or evening time use.
■Bath water can be re-heated indirectly by stored hot water.
3. Advantages of CO2 water heater
Hot water storage tankHeat pump unit
Kitchen RC Bathroom RC
water
Hotwater
Hotwater
water
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■ Environment-friendly.CO2 emissions: about 2/3-1/2 of gas water heater
■SafeHeats water up to 90°C without flame
■Energy efficient against conventional resistive heater system ・Annual average COP = 3.0 or higher
■Incentive & Low running cost・ Heat water at mid-night when electric power
is cheaper under current electricity rate in Japan→Running cost is about 1/4 to 1/5 that of gas
・Cost comparison with European Average gas and electricity shows little cost merit.
(See right figure)
3. Advantages of CO2 water heater
0
50
100
150
200
250
300
350
0 1 2 3 4 5 6 7
Resistive heater(EU)
Heat Pump(EU)
COP
Running Cost Comparison
Rel
ativ
e C
ost (
Gas
=100
)Gas
0
0.1
0.2
0.3
0.4
(kgC
O2/k
Wh)
1 2 3 4 5COP
Gas
Heat pump
Resistive heater
CO2 emission per heat in Japan
Heat Pump(Jp Mid-night)
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■ Electricity rate is determined according to the demand and the supply correlation. The water heater is operated to maximize the benefit of this kind of rate system.
Heating water at mid-night
0
5
10
15
20
25
30
35
43210 98765 1413121110 1918171615 23222120 24
Mid Night time¥7.22/kWh
DaytimeSummer:\29.76/kWhOther seasons:\27.06/kWh
Evening time\20.67/kWh
Morning time\20.67/kWh
Time [O’clock]
Pric
e [\/
kWh]
Mid Night time¥7.22/kWh
Electricity rates by time and season(KANSAI ELECTRIC POWER CO.)
3. Advantages of CO2 water heater
*web of KEPCO 2008
10DAIKINDAIKIN4. Technological development of major components
Development of swing compressor
Vane
IntakeCompression chamber
Roller
Crankshaft
At the tip of vane:・ Wear, abrasion・ Gas leak
Rotary compressor
Swing bush
CrankshaftPiston
Combined vane and roller:・ No wear, improved reliability・ Improved performance due to
less leakage
Swing compressor
■ Operating pressure of CO2 is higher than R410A, so it enhances the merit of swing compressor. Combined vane and roller of swing compressor achieves higher reliability and lower leakage than conventional design.
Refrigerant R410A CO2
Discharge pressure [MPa] 3.0 12.0
Intake pressure [MPa] 0.8 3.5
Pressure difference[MPa] 2.2 8.5Sound Velocity [m/sec at 50°C 1MPa]
192 273
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Traditional DevelopedSpec Double tube
1.00Weight ratio 1.00 0.74 0.64Performance 1.00 1.00 1.00
Smooth tube (initial)
0.89
Dimpled (latest)
Outline of shape
Volume ratio 0.89
CO2
Water
p
Dw
,iWater tubeCO2 tube
Dimple
Water
Leakage detection
ditchCO2
Comparison of water heater exchanger
Photo of appearance of water heat exchanger
■ The weight and volume of the dimpled water heat exchanger is about 10 to 30% less than those of a double-tube exchanger.
4. Technological development of major components
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Flow direction
Turbulent flow occurs by a dimple.
4. Technological development of major components
Visualization of flow in a dimple tube■ Performance of the water heat exchanger improved by adopting the
dimpled heat transfer pipe (SD tube) in the water side.・Heat transfer is doubled from smooth tube.・Enhanced heat transmission can be seen especially in low Reynolds flow.
Re
0
1
2
3
Nu/
Nu0
SD tubeInner grooved tube
0 2000 4000 6000 8000
Smooth tube
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Principle of expander cycle
5. Steps for the next generation CO2 water heater
■ Energy recovered by expander is transmitted to compressor to reduce power input.■ Cooling capacity increases because enthalpy of CO2 at expander exit decreases.
Enthalpy
CompressorInput
Heating CapacityExpanderCycle(IsentropicExpansion)
Pres
sure
Cooling Capacity
Conventional Cycle(Adiabatic Expansion)
EnergyRecovered byExpander
high
lowlow high
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■ The expander transmits the recovered energy directly to the compressorto reduce compressor power input.
Conventional type
Expander Compressor
Energyrecovery
M
Gas Cooler
Evaporator
Expansion valve
Adiabatic expansion (Energy is
not recovered)
Compressor
Gas Cooler
Evaporator
New Type
Function of expander compressor
M
5. Steps for the next generation CO2 water heater
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Expander-compressor
Cross Section Outlook
ExpanderInlet
ExpanderOutlet
CompressorDischarge
CompressorSuction
Expander
Compressor
DCMotor
■Connecting shaft transmit power from expander to compressor.⇒The technical development of water heater with this technology has
been carried out under NEDO (New Energy and Industrial Technology Development Organization of Japan) financial support project.
5. Steps for the next generation CO2 water heater
Connecting shaft
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- CO2 is suitable for high temperature water heaters because it has low GWP and equivalent COP. In addition, it can heat water to temperatures up to 90°C without a heater.
- For domestic use, both the user and the electric power company can benefit from CO2 heat pump operation at mid night.→ The user can reduce the operating cost while the power company can
level electric power load.
- In Japan, commercialization of residential CO2 heat pump water heater started in 2001. Accumulated sales exceeded 1 million units in 2007.
- By development of water heat exchangers, expander-compressor, other key components, and improvement of system technology, heat pump in the future may make a greater contribution to the challenge against global warming.
- This kind of thermal storage system may be useful to developing countries where nuclear or uncontrolable natural energy such as wind power is utilized.
6. Conclusion
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Thank you for your attention!
DAIKINWe want to contribute to a global environment through heat pump technology ⇒Slogan ; “Heat pump relieve the earth”
Acknowledgement ;・NEDO・Central Research Institute of Electric Power Industry・The Federation of Electric Power Companies of Japan・Tokyo , Kansai , Chubu , and Kyushu Electric Power Company