Keywords

Y2

deviceZ4

electricity

renewable energy

LTechnical Services

Heat Pump & Thermal Storage Technology Center of Japan

Thermal Storage Air Conditioning SystemFeatures
The thermal storage air conditioning system activates heat pumps during the night when energy demandis low, in addition to daytime hours when the building is supplied with conditioned air, to store thermalenergy in the form of chilled water, ice and hot water so that they can be used during the day.
An extremely efficient system can be built by combining thermal storage with high-efficiency heat pumps.
With conventional air conditioning systems that do not use thermal storage, equipment is shut down
completely during the night and the heat pump is activated during the day to supply hot and cool air.
On the other hand, with thermal storage air conditioning, heat pumps are activated during the night whenenergy demand is low to store thermal energy in thermal storage tanks. Chilled water and ice are stored
in the tanks for cooling purposes, and hot water for either heating or hot water supply. During daytime of
the next day when demand is high, thermal energy is drawn from the thermal storage tank for cooling,heating or to supply hot water.
NightConventional Air Conditioning

Does not operate at night.

Day

Building is heated orcooled during the day byexternal units.

NightDay

Heat Storage Air Condition

Thermal energy is stored
in a thermal storage tank.
The heat source unit runs on lessexpensive nighttime electricity andstores chilled water (ice) during thesummer and warm water in the winter.

Energy in the thermal
storage tank is used forheating and cooling.

Air condition uses chilled water (ice)and warm water from the thermal
storage tank during the day.

Basic Concept or Summary
The most appropriate type of thermal storage air conditioning system such as water-type or ice-typesystem can be selected depending on the scale and size of the installation space.

Water pipe
Air conditioning
unit

Water pipe

Air duct

Air conditioning
unit

Underground slab
Thermal water tank

Water thermal storage system Ice thermal storage system(unit type)Day time:
Take out and use
Perform rated operation of heat pumpNight time: Store heatin thermal storage tank

22:00

8:00

18:00 22:00

Heat pump capacity

Thermalice tank

HalvedHeat source unitAir duct

Thermal storagesystem

Heat source
unit

Conventional system

Water thermal storage system
Underground space which is usually left unused (underground pit) is used as the thermal storage tank.
The water in the thermal storage tank can be used for extinguishing fires or for domestic use during
disasters or emergencies.
Ice thermal storage system
Ice is made in the thermal storage tank to store cold energy.
The tank size can be kept smaller than with water thermal storage tanks.
The thermal storage air conditioning system responds to peaks in cooling loads during the day by combining
cold energy stored during the night with that produced during daytime. Consequently, the size of theinstallation capacity can be kept to almost half that of systems that do not utilize thermal storage.
Air conditioning demand in midsummer

O-05

S5

Effects or Remarks

O-05

S Reduction in the daytime peak power demand (power load leveling)
The leveling of power load can be achieved as the system can transfer the power used during the peak
hours in the daytime to the nighttime.
Introduction of the heat pump/thermal storage system makes approx. 20 % reduction in the daytime
peak power demand by supplying half the cold thermal energy required for the air-conditioning
during the daytime from the thermal storage system.
S Utilization for demand response
Demands can be suppressed and created when a demand response directive is issued, by regulating
the amount of heat stored in the thermal storage tank and the amount of heat drawn from the thermal
storage tank.
S Energy conservation and environmental friendliness
The use of thermal storage tanks makes it possible to operate heat pumps efficiently at a constant rate
without being affected by ever-changing air-conditioning load.
The use of the cool outside air in the night for the generation of cold thermal energy when cooling isrequired leads to further improvement in the efficiency of the heat pumps.
(The operational efficiency of the heat pump at 25 degrees is approx. 20% better than at 35 degrees.)
S Cost saving
As this system allows the reduction in the capacity of the heat source unit, the contract demand can bereduced. The reduction in the contract demand means the reduction in the electricity charge.
This system allows the use of lower-priced nighttime power.
S As a measure of BCP (Business Continuity Plan)
The water in the thermal storage tanks can be used as domestic water or for firefighting at the time ofemergency and disaster.
There were cases where water in thermal storage tanks was used as domestic water in the relief effort
after the Great East Japan Earthquake.
In the event of an emergency, water can be utilized to extinguish fire or domestic use.
A case of the operation of the thermal storage air-conditioning
system in an office building (in Kanto Region, in the summer)(Power consumption)

Daytime peak power demandwhen the thermal storage
system is not used

Daytimepeak power
demandreduced byapprox.
20 %Thermal radiationin the non-shaded
parts.

Duringpower
outageIn case of emergency
or disasterAir
conditioner

Water utilized for domestic use
Face and hand washing, etc.
Filtering unit

Daytime peak power
demand when
the thermal storage
system is used

Efficient thermal storageat a constant rate

Daytime power
reduction

In case of fire
Used for extinguishing fire

Emergency
power supply

Air-conditioning(heat source)

Air-conditioning(delivery etc.)(Hours)Lighting,elevators, etc.
* A model case of an office building

An example of the operation of the system in an office building

Stopped due topower outage

Heat pumpTemporary toilet

Duringpower outage

Thermal water tank(use of heatfrom thermalstorage tank)

Use of the system at the time of disaster

Installation in Practice or Schedule
Domestic

Number of installations: 33,345 (as of the end of FY 2021 estimate)
Peak shift effect in domestic power demand from thermal storage air conditioning systeminstallation: 2.15 million kW (FY 2020 estimate)u Number of Heat Storage Air Conditioning Systems Installedmillion kW

33,345 installations
Peak shift kW
Number of installations

Contact:

Number2.15 million kW

Heat Pump and Thermal Storage Technology Center of Japan
International & Technical Research Department
1-28-5 Hulic Kakigaracho Bldg., 6F, Kakigaracho Nihonbashi, Chuo-ku, Tokyo, Japan
Tel: +81-3-5643-2404 Fax: +81-3-5641-4501 URL: http://www.hptcj.or.jp/e/index.html