Monthly Engineering Horizons

THE BENEFITS OF ICE THERMAL STORAGE SYSTEMS

THE BENEFITS OF ICE THERMAL STORAGE SYSTEMS

February 16
14:42 2019

By: Muhammad Saghir Khan, Chief Executive, Energy Associates Building Services Consultants Inc. Ontario, Canada.

ABSTRACT

Today, as many electric utilities worldwide approach their electrical generating limitations, particularly during peak demand hours on summer afternoons, the energy efficiency can involve using less energy, but it can also mean using energy more effectively.

Thermal Storage allows cooling to be produced at night for use the following day (typically during time of peak demand) this improves efficiency for utilities because it allows them to service more customers with the same generating capacity and or flatten out their production profiles.

The resulting lower cost of utility operation can be passed on to customers in the form of lower rates-particularly for off – peak consumption. The use of ice thermal energy storage (TES) technologies has been thoroughly proven as a viable demand side management strategy.  The TES system can build ice during off-peak electrical demand times, typically at night, for use during peak electrical demand periods, when electrical rates are high, to provide comfort and process cooling.

To assess the practicality and potential for achieving total energy savings, approximately 59 % of the energy in Pakistan is used in the Buildings, out of that 25-30 % are consumed by Building Air Conditioning cooling systems.

The foregoing article is discussing the energy conservation measures in building sectors.

Pakistan should encourage energy efficiency and energy conservation, which would result in significant reduction of primary energy demand. Additionally a Serious thrust to change its energy mixes lead to greater self-reliance, energy security, a lower import bill, better power availability and targeted assistance to the poorest in society. At the same time pricing policies will allow for changes in customer behavior leading to reduce energy demand, improved energy efficiency and greater motivation for energy conservation. All of the above is necessary for Pakistan’ economic survival and progress since it has to compete with the world for the supply of petroleum products, which it imports to fulfill a significant proportion fits primary energy.

If TES achieved a 15-20% market penetration by coming years enough source energy would be saved from load shifting only (ignoring kWh impacts) to supply the energy needs of over a fifth of all new air conditioning growth projected by the local power supplies companies during the next decade.

A comparison was established between the various thermal storage systems for study to implement for project to use ice thermal storage system for implementation cost, Services life and First Cost, Operation and Maintenance requirements, Regulations & Code Compliances. Finally conclusions and recommendations were made for future investigation to provide objective information, which is required to produce design and operational guidelines for the total energy savings, environmental benefits,  (which is not part of subject Article) for the Ice Thermal Energy Storage Systems.

  1. INTRODUCTION

In most Provinces of Pakistan, industrial consumers pay separate charges for electrical energy (kWh) consumed and maximum KVA or KW demand. Time of Use tariff has been introduced in many parts of world and in Pakistan also getting under way as well, considering the different tariff time zones for High Tension consumers; the off-peak energy tariff, between 10 pm to 6 am, is going to be about 30% of the peak time rate. This provides an incentive for users to shift their large loads to off-peak period (nighttime). Consumers with large refrigeration and air-conditioning load can use the concept of the small storage to reduce their maximum demand and also peak time energy consumption.

The use of Thermal storage has the potential of total energy savings in many numbers of ways, such as eliminating the operation of “intermediate” and “peak load” power plants at the peak demand load, which has highest operating cost and typically lowest efficiency.  The cost to produce a kWh of electricity is highest during the on- peak hours because the least efficient power plants run during these on – peak hours, hence the costs of generating the electrical “energy” are higher during these hours and most of time it end up the load shedding due to power generation incapacity.

In order to keep over –all electricity costs down, the electric utilities run their most economic and typically most efficient “ base load” power plants as much as possible. This leads to a situation in which electricity users can reduce their electricity costs under Time-of use rates if they can reduce their peak electricity use. TES provides electricity users that opportunity, as summarizes below.

An Electric utility’s costs and prices are much higher during on-peak hours. An Energy user who uses less on –peak electricity can save significant amount of money. By decreasing Chiller operation during utility peak period., demand charges are reduced.

Thermal Energy storage reduces on-peak electricity use

The general belief is that TES reduces the fuel or energy required at the source by changing the time at which KWhs of electricity is used. It has been postulated by a number researchers and power utilities that some of the features of T.E.S. that leads to improved site energy savings such as operation of fully loaded Chillers, Cooler night time temperature, enhanced heat recovery, and in distribution systems lower volume of cooler water moved by pumps Thus, the more often the cooling load operates at less than its design capacity, the better the performance of the TES system compared to a conventional cooling system.

  1. CURRENT DESIGN PRACTICE FOR REFRIGERATION & A/C SYSTEMS IN PAKISTAN

Pakistan, being a warm tropical country, most of the refrigeration and HVAC applications involve cooling of air, water, other fluids or products. Heating issued only for a very small period in winter in the northern parts of the country and in places at high altitudes.

Refrigeration and Air-conditioning accounts for assign if cant portion of the energy consumption in many manufacturing industries(like chemicals, pharmaceuticals, dairy, food etc.),Agricultural & Horticultural sectors(mainly cold stores) and commercial buildings(like hotels, hospitals, offices, airports, theatres, auditoria, multiplexes, data processing centers, telecom switch in exchanges etc).

 

Refrigeration and air conditioning systems cover a wide variety of cooling applications, using both standard and custom-made equipment. The most commonly used systems for industrial and commercial refrigeration and air conditioning are VA pour Compression Refrigeration System and Vapour Absorption Refrigeration System. Vapour compression machines, usually with electrically driven compressors, are the most commonly usedmachinesforrefrigerationandairconditioningfortemperaturesranging from 25°Cto-50°C. Vapour Absorption Refrigeration machines, wherein heat energy is consumed; Absorption refrigeration machines may be economical in situations where process waste heat or cheap fuels (usually coaloragro-waste)are available. In recent decades with the reduction of natural gas availability with in the country the engine driven vapour compression systems are being used which has increased the Power demand for Building sector up to 59% out of that 25-30 % are consumed by Building Air Conditioning cooling systems. The energy cost of refrigeration and air conditioning systems may be about six (6) to ten (10) times their first cost during their life time.  In corporation of energy efficiency in to the design and application of the Air conditioning Systems can pay rich dividends, which can be achieved through Demand side Managements by applications Thermal energy storage systems.

  1. THERMAL ENERGY STORAGE SYSTEMS AVAILABLE TECHNOLOGIES.

In many parts of the world, notably in North America and Middle East, cooling systems use a greater proportion of electricity for cooling and commercial consumers are heavily penalized by electricity supply companies for energy use in the summer time. As a consequence a consider amount of the work has been carried out on ice storage systems to reduce summertime maximum demand.

In most provinces of Pakistan the situation is as follow:

The maximum electrical demand on the power plants to occur in the summer months of June and July due to considerable air conditioning load in the region.

The Refrigeration energy used in an air-conditioned office building can be described as a “first order” component of electrical energy use. The “second order” of air conditioning energy is that used by fans, pumps that are approximately 20% of the electrical energy used by an air-conditioned office building.

  • CHILLED WATER STORAGE SYSTEMS.

These Systems use the sensible heat capacity of water to store Cooling. The tank volume depends on the temperature difference between the water supplied from the storage and the water returning from the load and the degree of separation between warm and cold water in the storage tank.

  • ICE STORAGE SYSTEMS.

The refrigeration machines are used to charge the ice store during the night-time, with the stored cooling energy discharged during the day to offset the heat gains of the building. It uses the latent heat of fusion and thawing the ice store as the mechanism for transferring energy and is mainly used for summer time load shifting.

Advantages of the system include a reduction in capacity of refrigeration plant and hence the capital cost of the chillers. As the chillers could be up to 50% smaller and therefore possess up to 50% less refrigerant, the method offers an effective way of reducing the amount of refrigerant in use. With ice storage installations, the chillers will generally be ran during the night to charge the store, overnight temperatures are lower and consequently condensing pressure will be lower, hence the COP of the chillers will be improved.

A full load storage system will use the most energy – the ice storage meets the total cooling load for the day. A partial load system is one where the combined ice store and chiller meet the cooling load of the day. A study shows that the refrigeration energy consumed over an annual cooling season will be 20% more than that of conventional installations.

 

The largest cost savings can be obtained at a high peak to off- peak ratio and at short peak periods.

A Brine –Coil Ice Storage System.,  (a)

SCHEMATIC DIAGRAM (B)PARTIAL STORAGE TIME SCHEDULE (C) ICE PRODUCTION  (D)  ICE MELTING.

  • CRITIQUES ON DIFFERENET TYPES OF ICE STORAGE

 

The Ice stores can be divided into two types   Static & dynamic.  Most of the dynamic ice storage originate from commercial ice making equipment and are common in the USA used predominately on large installations. Static ice storage are more commonly the type used in Europe.

 

Static ice storage

The static ice storage are ones where ice is charged and discharged in one place and is not transported around the air conditioning system. The various types of storages systems are detailed in Dorgan. C.E.{1994} & J.S. Elleson {1994.}

 

  1. External melt ice-on-coil. Ice is formed on the outer surface of submerged pipes or tubes through which a refrigerant or secondary coolant is circulated. Cooling is discharged by circulating warm return water through the tank, melting the ice from the outside.
  2. ii) Internal melt ice-on-coil.  Ice is formed on submerged pipes or tubes, similarly to the external melt system. Circulating warm coolant though the pipes, melting the ice from the inside, discharges cooling.

iii )           Encapsulated ice.  Water that is sealed inside submerged plastic container freezes and thaws as cold or warm coolant is circulated through the tank that holds the containers

 

DYNAMIC ICE STORAGE

These systems allow the transportation of the ice around the system in direct contact with the working fluid, and this is not part of this Article study. (Ice Harvesting, Ice slurry storage, Phase –Change Material.)

 

 

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Engineering Horizons

Engineering Horizons

“Engineering Horizons” is the first & leading technical magazine of Pakistan covering Process, Mechanical, Metallurgical, Mining, Electrical & Electronics field under a single cover. We also feel pleasure in saying that this is the only magazine of its own kind & style, which is widely circulated in all Engineering Sectors of Pakistan.

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As you know, monthly “Engineering Horizons” is the first & Leading Technical Magazine of Pakistan covering Process, Mechanical, Metallurgical, Mining, Electrical & Electronics fields under a single cover. We also feel pleasure in saying that this is the only magazine of its own kind & style, which is widely circulated in all Engineering Sectors of Pakistan.
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