Energy saving effect by air circulation heat storage ... · PCM UNIT, simultaneously with the heat...
Transcript of Energy saving effect by air circulation heat storage ... · PCM UNIT, simultaneously with the heat...
Energy saving effect by air circulation heat storage system
using natural energy
李 学成
1. Introduction
In the field of housing and buildings, the final
energy consumption is accounted for more than 30%
in Japan. The increase in energy consumption and CO2
emissions from the past is remarkable and plays a
major role in realizing a low-carbon society. Thus
further strengthening of energy conservation
measures is required1). In this study, the development
of a system is aimed at reducing sensible heat load
and peak load in a detached house by employing air
circulation type of central air conditioning system
using PCM UNIT, which has latent heat storage effect.
The system is maximized by applying the air
circulation through the roof ventilation layer, by
which heat exhaust and radiation cooling in summer
/ the heat collection in winter are performed. It
is expected that the system can be introduced into
ventilation layer provided in a conventional house.
2. Experiment on PCM BOX
A latent heat storage material (hereinafter
referred to as PCM: Phase Change Material) is a heat
storage material utilizing latent heat (heat
absorption during melting/heat release during
solidification) when a substance undergoes a phase
change from solid to liquid or from liquid to solid.
Figure 2.1.(a) shows the interior of the
experimental room, and Figure 2.1.(b) to (d) shows
the condition of PCM BOX. Small joists (thickness
6mm, width 25mm) are installed on both sides of PCM
packing component. The internal dimension of the box
is 300mm×300mm×300mm. The outside surface of the
XPS (Styrofoam) is affixed with an aluminum tape.
The number of ventilation can be regarded as 0
times/h because the box is sealed as much as
possible. The experiment is set to three levels: (a)
Blank (without PCM), (b) PCM 1st layer (PCM exposed
on the inner surface of the box), (c) PCM 2nd layer
(PCM placed on the back side of the floor).
(a) (b)
(c) (d)
Figure 2.1. Experimental conditions: (a) interior of
experimental room, (b) Case 1: Blank box (without PCM),
(c) Case 2: PCM_first layer, (d) Case 3: PCM_second
layer
2.2. Results of measurement and calculation
The experimental results were verified by using a
software THERB for HAM2), which is combined
simulation of heat and moisture transfer, and air
flow. The thermal environmental condition in the
experimental room is the temperature of 23℃ and the
relative humidity of 50% in curing time. When
measuring, the temperature is 23±7℃ (24 hour
period) and the relative humidity is 50%. Figure 2.2
shows the measurement result of the temperature. It
can be confirmed that PCM absorbs the heat during
melting in the heating process and releases the heat
in solidification in the cooling process through the
temperature change of the PCM surface. Thus, the
effect of thermal regulation and the peak
temperature reduction by PCM are found. The larger
storage capacity of Case 2, where PCM is exposed to
the air inside PCM BOX, is considered than Case 3,
comparing the temperature inside PCM BOX.
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LDK
BathroomBathroom
Wash room
Wash room
Entrance
Location Yufuin, Oita Prefecture, Japan
Total floor area 235.61 m2
Area classification Area 5
Annual insolation area classification A3
Insolation area classification
in heating season H2
Mean heat transmission coefficient of
external wall 0.34/(m2 ∙K)
Japanese-style
room
Bedroom1
Bedroom2Bedroom3Bedroom4
Air conditioning
machine room
W.C.W.C.
Figure 3.1. Experimental house
Table 3.1. Overview of experimental house
Figure 3.2. Section of roof
Figure 3.3. Plan of experimental house
<Route ①>
Figure 3.4. Example of Summer route of air circulation
1F 2F
3. Analysis of effect of reduction in sensible heat load
3.1. Overview of experimental house
Figure 3.1 shows the exterior of the experimental
house and Table 3.1 shows the overview of the house,
which is located in Yufuin, Oita prefecture, Japan.
Figure 3.2 and Figure 3.3 show the cross section of
roof and the plan, respectively, and temperature
measurement point. Measurement of thermal
environments such as the internal temperature of the
roof ventilation layer (eaves, center, ridge), indoor
temperature and humidity, internal wall temperature
and humidity, external weather have been performed.
3.2. Air circulation route
(1) Summer mode
Figure 3.4 shows the air circulation route in the
summer mode. Firstly, since the temperature of the
roof ventilation layer can be expected to decrease
by radiative cooling at night, when the temperature
of the center of the roof ventilation layer is 25℃
or less, indoor air is taken into the roof
ventilation layer and blown to the PCM UNIT,
simultaneously with the cold storage in the PCM, and
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Inside of box (measured) Inside of box (calculated)
PCM surface (measured) PCM surface (calculated)
Case 2:Back surface of plywood, Case 3 : Surface of plywood (measured) Case 2:Back surface of plywood, Case 3 : Surface of plywood (calculated)
Experimental room
Figure 2.2. Results of measurement and calculation. (left: Case1, center: Case2, right: Case 3)
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Average outside air temperature
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Latent heat load of air conditioner [kWh/day] Average temperature of outside air [℃]
Average temperature in the center of ventilation layer [℃] The time of temperature below 25℃ in ventilation layer [h]
Figure 3.5. Amount of radiative cooling
(August, 2016)
Figure 3.6. Change in heat quantity
(August, 2016)
Figure 3.7. Integrated quantity of
cold storage and release (August, 2016)
Figure 3.8. Temperature change in
roof ventilation layer (August 2016)
then the air is moved to the air conditioning room
(night cooling: route ①). Meanwhile, in the daytime,
the center temperature of the roof ventilation layer
becomes 25℃ or more, so indoor air is blown to PCM
UNIT by Fan B, without passing through the
ventilation layer, and then, the cold stored at night
is recovered and sent to the air conditioning room
(daytime cooling: route ②). At the same time, since
the roof ventilation layer becomes high temperature
due to solar radiation reception during the daytime,
the forced fan operates to take in outside air and
exhaust heat in the roof ventilation layer (daytime
heat exhaust: route ③). Through these air
circulation route, the effect of reducing the
sensible heat load in the daytime can be expected by
releasing the cold stored in the PCM at night
(2) Winter mode
Firstly, since the temperature of the roof
ventilation layer can be expected to increase by
solar radiation in the daytime, when the temperature
the center of the roof ventilation layer is 25℃ or
more, the indoor air is taken into the roof
ventilation layer by forced fan A, and blown to the
PCM UNIT, simultaneously with the heat storage in
the PCM. And then, the air is moved to the air
conditioning room (daytime heating: route ①).
Meanwhile, at nighttime, the temperature of the roof
ventilation layer becomes 25℃ or less, so indoor
air is blown to PCM UNIT by fan B without passing
through the ventilation layer, and the collected
heat stored at night is recovered and sent to the
air-conditioning room (night heating: route ②).
Through these air circulation route, the effect of
reducing the sensible heat load at nighttime can be
expected by releasing the heat stored in the PCM
during the daytime
4. Results of actual measurement and calculation
4.1 Analysis of actual measurement
Figure 3.5~3.8 show the effect in summer mode,
which is the radiative cooling, the change in heat
quantity in PCM BOX, the integrated quantity of cold
storage, and the temperature change in the roof
ventilation layer, respectively. The sensible heat
load is reduced in the summer because cooled air is
blown into the air conditioning room according to
the cold energy released a maximum of 6.6kWh/day by
PCM during the daytime. Figure 3.9~3.12 show the
effect in winter mode. The sensible heat load is
reduced in winter because heat air is blown into the
air conditioning room according to the hot energy
released a maximum of 6.2kWh/day by PCM during night.
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Bedroom 2 temperature
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Heat collection amount[kWh/day] Sensible heat load of air conditioner [kWh/day]
Latent heat load of air conditioner [kWh/day] Average temperature of outside air [℃]
Average center temperature of ventilation layer [℃] The time of temperature above 25℃ in ventilation layer [h]
Solar radiation[kWh/m2・day]
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bedroom 2 temperature Eaves side temperature of ventilation layer
Ridge side temperature of ventilation layer
Figure 3.11. Change in heat quantity
(November, 2016) Figure 3.12. Integrated quantity of heat
storage and release (November, 2016)
Figure 3.9. Temperature change in roof
ventilation layer (November, 2016)
Figure 3.10. Amount of heat collection
(November, 2016)
4.2. Comparison of measured and calculated value
Figure 3.13 shows the comparison of the measured
and calculated temperature change by THERB for HAM
in winter mode, which is susceptible spaces to air
circulation in the roof ventilation layer or the
amount of solar radiation. The calculated value
matches the measured value with high accuracy, and
the high accuracy of the calculation is confirmed.
4.3. Effect of reduction in sensible heat load
Figure 3.14 shows calculation result in order to
confirm the effect of the reduction in the sensible
heat load of the whole building in winter. Case 1
is each room air conditioning, Case 2 is air
circulation system using roof ventilation layer, and
Case 3 is case 2 with PCM UNIT. The rate of reduction
about 28% by using the system is evaluated in both
summer and winter in comparison with Case 1. The
total sensible heat load between Case 2 and Case 3
does not show clear distinction because PCM store
and release repeatedly in order to decrease peak-
load or overheating.
5. Conclusion
The effect of reduction in sensible heat of the
air circulation system with PCM UNIT is confirmed.
The heat storage amount of 6kWh/day and the
reduction in sensible heat about 28% was evaluated
in comparison of each room air conditioning.
Reference 1) METI, Ministry of Land, Infrastructure and Transport,
Ministry of the Environment : Interim summary on measures to promote "Housing and living for low-carbon society", July, 2012
2) Ozaki A. : Combined Simulation of Heat and Air and Moisture on the Hygrothermal Environment and Heating / Cooling Load,Technical Papers of Annual Meeting of IBPSA-Japan,pp.19-26,2005
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GJ/
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Figure 3.13. Comparison of indoor temperature change,
November, 2016 (From above, Bedroom2, Attic space, LDK)
Figure 3.14. Reduction in sensible heat load (January,
standard year, Extended AMeDAS weather data)
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