SOLAR  ABSORPTION  COOLING  PROJECT  FOR  GREECE

Dr. HIRSCH

Solar Powered Cooling Plant for Central Air Conditioning

Solar powered cooling plant for air-conditioning is equipped with the following main systems and components:

(1)          Solar Collectors Array

(2)          Absorption Water Cooling Machine (Absorption Chiller)

(3)          Hot and/or Cold Water Storage (option)

(4)          Piping and Accessories

(5)          Control System

Description - Solar Collectors Array

A solar collector array supplies hot water as a source of energy to the absorption cooling machine through hot storage. The collectors are based on technologies which can supply hot water at relatively high temperature (90-150 degC).

(2)          Absorption Water Cooling Machine (Absorption Chiller)

 An absorption chiller supplies chilled water to the central chilled water plant of the central air-conditioning system.The chiller is powered by heat of the hot water supplied by the collectors array.The chiller plant includes also a cooling tower or air cooled condenser in order to eject the chiller condenser and absorber heat.   

Backup is supplied by means of additional heat source (conventional fuel heated boiler and/or by existing electric powered chillers).

(3)          Hot and/or Cold Water Storage

A thermal storage system (hot and/or cold) is integrated with the plant. The storage system ensures stable supply of chilled water during day-time or even during evening depending on total solar radiation energy collected during day-time, building cooling load time-profile, time-of-day electrical tariff, etc.

(4)          Piping and Accessories

 Hot water piping & accessories systems are installed in the following closed loops:

     Hot Water

Closed hot water loop connects the solar collectors array with the absorption chiller through the hot water storage.

     Chilled Water

Closed chilled water loop connects the absorption chiller through the cold water storage (optional) with the chilled water plant of the building.

  Condensing and Absorption Water

Closed water loop connects the absorption chiller with the cooling tower.

The piping loops are equipped with all required accessories (manual valves, water flow regulators, automatic 2-Way and/or 3-Way control valves, air vents, water drains, expansion tanks, etc.)

         Control System

 A computerized control system is equipped in the plant order to ensure optimal operation of the plant: i.e.: maximizing the energy and cost  benefits achieved by the plant and minimizing operational cost of the solar powered plant and of the existing electric powered chilled water plant.

 1.2. Performance Aspects - General

 Performance aspects relate mainly to the solar collector array, to the absorption chiller, to the heat source backup and to the integration to a complete system combined with thermal storage and energy management & control. Following short discussion of the main aspects:

Description - Solar Collectors Array

The efficiency of regular flat plate collectors is relatively high (up to 50%) at relatively low domestic hot water temperature applications (up to 60 degC) but is low at higher temperature range.

Since absorption chiller COP (coefficient of performance) increase with increasing of the heat source temperature regular flat plate collectors are not suitable to be used as a heat source to operate absorption chillers; modified technologies which supply heating at higher temperature ranges at relatively high temperature are required.

Existing technologies for higher temperature range are in the following spectrum:

·      Flat plate collectors with modified coating collecting surface, insulation and glazing. The range of temperature is 70 - 95 degC at efficiency range of 50% - 40%.

·      Concentration collectors at low concentration ratio for a temperature range higher than 100 degC (e.g.: 120-140 degC) at efficiency range of 50% - 60%. Various types of technologies are existing.

The cost of  technologies is varied in a wide range depending on the specific technology and the specific manufacturer. The range is 100 - 200 $/sqM.

 (2)   Absorption Water Cooling Machine (Absorption Chiller)

Absorption chiller COP (coefficient of performance) varies in a range of 0.5 - 1.2 within heat source temperature range of 70 - 140 - depending on the specific technology and staging and on the specific manufacturer (COP definition: the relationship between thermal power of cooling the chilled water and thermal power of heat supplied to the chiller as a forcing power).

Rules of thumb  indicate specific solar collector area in a range of 8 - 22 sqM/1 TR (Ton of Refrigeration). This wide range means that optimization has to be done in the overall system integration design. 

Sometimes conventional heat source is required as a backup (depending on fuel price with comparison to electricity price) in periods of time when solar heat source power is at low level. In generally conventional absorption chillers technologies offer poor performance backup which supply heat to the common heat inlet of the solar heat source to the chiller. Contrary advanced technologies have to be integrated in order to prevent solar collector array efficiency reduction due to negative effects.

  2.  An Advanced Technology Presentation

During the late 70’s and at the beginning of 80’s, way before the era of broadband connections, an advanced technology  - for solar energy collection, absorption cooling, energy management & control - was developed in Israel in the frame of an Energy National Program of the Israeli Ministry of Energy & Infrastructure. The development was performed by an engineering team in a big Israeli industrial firm. Dr. Moshe Hirsch was member in this team and was a project manager of a solar powered cooling system based on Rankine Cycle and a project manager of total energy system optimization and control.

Following some data concerning the performance of the system:

(1)   Solar Collectors

An advanced collectors flat plate technology - based on unique selective coating, insulation and glazing -  was developed in order to supply hot water in a temperature range of 60 - 95 degC at relatively high efficiency of 60% at 60 degC and 35% at 95 degC.

The application was for total climate control:

·      domestic hot water

·      space heating

·      absorption cooling

 (2)   Absorption Water Cooling Machine (Absorption Chiller)

An advanced solar absorption chiller technology was developed at capacity ranges of 24 - 200 TR (ton of refrigeration).

The unique advantages of the technology were:

·      elimination of crystallization at low part load or at low condenser water temperature

·      COP value of 0.72 at 80 degC

·      staging for backup (hot water at 80-120 degC) without negative effect on solar energy collection efficiency.

(3)   Total System Integration & Control

An advanced overhaul system integration was performed including thermal storage and microprocessor & computerized based  control in order to utilize maximum potential of solar energy.

A large system (collector array: 4,000 sqM (brute), absorption cooling machine: 200 TR) was applied at 1981-1982 as a demonstration project for cooling at a medical center. The project was partially financially supported by Israeli Ministry of Energy & Infrastructure. Dr. Moshe Hirsch was at that time the project referee  at the Israeli Ministry of Energy & Infrastructure and prepared the follow-up, the project and the whole  multiyear program summary reports. 

Summer data showed capacity above 200 TR. Winter capacity (sunny day time with relatively low condensing water temperature) showed above 160 TR. Due to thermal storage application cooling was achieved even at night.