Environmental Engineering Reference
In-Depth Information
4.10.1 Air-conditioning thermal energy storage (ACTES)
The air-conditioning thermal energy storage (ACTES) units work with the air
conditioning in buildings by using off-peak power to drive the chiller to create
ice. During the day, this ice can be used to provide the cooling load for the air
conditioner. This improves the overall effi ciency of the cycle as chillers are much
more effi cient when operated at night time due to the lower external temperatures.
Also, if ACTES units are used, the size of the chiller and ducts can be reduced.
Chillers are designed to cope with the hottest part of the hottest day possible, all
day. Therefore, they are nearly always operating below full capacity. If ACTES
facilities are used, the chiller can be run at full capacity at night to make the ice
and also at full capacity during the day; with the ice compensating for shortfalls
in the chiller capacity. ACTES units lose approximately 1% of their energy during
storage [ 3 ].
4.10.1.1 Cost of ACTES
If ACTES is installed in an existing building, it costs from $250 to $500 per peak
kW shifted, and it has a payback period from 1 to 3 years. However, if installed
during construction, the cost saved by using smaller ducts (20-40% smaller), chill-
ers (40-60% smaller), fan motors, air handlers and water pumps will generally pay
for the price of the ACTES unit. As well as this, the overall air conditioning cost
is reduced by 20-60% [3].
4.10.1.2 Future of ACTES
Due to the number of successful installations that have already occurred, this tech-
nology is expected to grow signifi cantly where air-conditioning is a necessity. It
is however, dependent on the future market charges that apply, as this technology
benefi ts signifi cantly from cheaper off-peak power and demand charges. Finally,
ACTES units will have to compete with other building upgrades such as lighting
and windows, for funding in the overall energy saving strategies enforced [3].
4.10.2 Thermal energy storage system
The TESS can also be used very effectively to increase the fl exibility within an
energy system. As mentioned previously in this chapter, by integrating various
sectors of an energy system, increased wind penetrations can be achieved due
to the additional fl exibility created. Unlike the HESS which enabled interactions
between the electricity, heat and transport sectors, TES only combines the elec-
tricity and heat sectors with one another. By introducing district heating into an
energy system, then electricity and heat can be provided from the same facility to
the energy system using combined heat and power (CHP) plants. This brings addi-
tional fl exibility to the system which enables larger penetrations of intermittent
renewable energy sources. To illustrate the fl exibility induced by TES on such a
system, a snapshot of the power during different scenarios is presented below. The
system in question contains a CHP plant, wind turbines, a thermal storage, a hot
water demand, and an electrical demand as illustrated in Fig. 19.
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