BASIC COMMERCIAL DESIGN GUIDE
 
SOLARDESIGN

The efficiency, cost-effectiveness and overall ability of a commercial solar heating system is completely dependent upon sound design knowledge and experience. Contact VM today to discuss the design process.

 

NOTE: The information presented in this page is for guidance only - no part of this may be used for any agreement, whether expressed or implied, or to form any contract. THERMO TECHNOLOGIES reserves the right to change specifications and prices without prior notice.

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General Information

This guide is prepared to provide basic technical information for large commercial or industrial size solar water heating systems. All the points mentioned in the guide have to be verified by M & E engineers according to local requirements and would be their responsibility.

Preliminary Load Estimate

The existing records of water heating fuel usage or hot water consumption are an excellent source of thermal data and should be used to estimate the load. If existing data or actual energy use are not available an estimate should be made based on typical use of hot water per day per person in the building.
When surveying a commercial or industrial site for possible installation of an active solar heating system, it should also be determined whether other sources of heat, such as gas burners, waste heat recovery, are available at the site.
Physical Constraints Once the construction of the building has been confirmed, the best location for the installation of the solar collector array as well as the storage tanks should be determined. Weight load permitted at the location where the collector array is to be installed must be considered. This is particularly important for the storage tanks. If possible, the storage tank should be located close to the solar collector array.
Conceptual System Selection An active solar water heating system collects, stores and distributes solar energy using liquid as the heat transfer media. The system includes solar collectors, thermal energy storage tank, load interface and system control unit and instrumentation.
Sizing of the Solar Heating System a) Collector area - Net absorber area of the collector could be determined by making use of the local solar radiation data.
b) Collector Slope and Orientation - The preferred field orientation is facing true south (in the Northern hemisphere), but deviation up to ± 30 º has minor impact on solar energy system performance and is acceptable to permit conformance with building orientation for roof-mounted collectors and reduction in installation costs.
The preferred collector slope angle is in the latitude.
c) Sizing storage tank - If time and rate of energy generated by a solar energy system does not coincide with energy needs, then thermal energy storage is required to store the excess generated energy until it is needed. Ideally, the storage capacity should be sufficient to store any excess energy at a temperature most beneficial to both energy collection and energy usage.
The size of the storage tank could be approximated according to the specification of the load pattern as well as the estimated average heating power output of the solar heating system. The economic aspect should be also considered for the selection of the tank size.
d) Sizing pipe line - Piping is required to route and control the flow of heat transfer fluid between various components of the solar subsystem. The objective of the piping design is to accomplish all these functions with the best compromise between minimum parasitic power requirements and minimum capital costs. The pipe size should be determined according to the flow rate required for the solar heating system, maximum allowable flow velocity as well as economic aspect.
e) Sizing Circulation Pumps - All solar water heating systems, except the thermosyphon type contain a pump set. The pump circulates the heat transfer fluid between the collector and the storage tank. Pumps should circulate heat transfer fluid at the design flow rate with minimum expenditure of electrical energy. Analysis of the complete pipe work will allow a total system head to be determined, describing variation of the total pressure drop of the system with operating flow rate. A suitable pump should provide the required flow rate at the necessary head while operating at or near its best efficiency.
The following table presents the typical design parameter ranges for solar water heating systems.
Collector Flow Rate [gpm/ft²] 0.05 - 0.07
Collector Slope (Latitude + 15 ° ) ± 15 °
Collector Orientation South ± 15 ° in Northern hemisphere
Heat Exchanger Rate per Collector Area[W/K m²] 40 - 80
Storage Capacity per Collector Area [Gallon/ ft²] 2 - 4
Overall System Schematic The initial step of the detail design effort should be the development of an overall solar energy system schematic. When completely developed, the schematic becomes a piping and instrumentation diagram and is the overall guide for the detail solar energy system design efforts. This diagram should graphically show or identify the following information:
1. Overall solar energy system configuration and interfaces with the loads and auxiliary energy sources
2. Major solar energy system components and their relative locations (collectors, heat exchangers, thermal storage tank, pumps)
3. Relative locations of the various pipe work components (valves, vents, expansion tank, relief valves, etc.)
4. Relative location of required sensors and instrumentation.
System Types The two commonly used kinds of commercial solar heating systems are as follows: System I is a solar heating system with an un-pressurized storage tank. System II is the system with pressurized storage tank.
   
  SYSTEM I
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System I In System I, the heat transfer fluid (ionized water) in the storage tank is vented to atmosphere. All heating is done on a low pressure basis (around atmosphere pressure). Heat is transferred to the potable water by way of a heat exchange coil within the storage tank.
The advantages of the system are that the entire system is at low pressure so only potable water flows through the heat exchange coil. As the stored potable water is at any time at a minimum, this means isolated pockets of water cannot stagnate and become Legionella breeding ground.
The disadvantages of the system are:
1) Higher collector loop pump capacity might be required to overcome elevation head between collector and storage tank.
2) Initial cost of antifreeze fluid can be higher.
 

 

SYSTEM II

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System II

In the system II, the heat transfer fluid (neutral water) is stored in the heat exchange coil as well as in the pipeline between the collector and storage tank. Potable water in the tank is heated by the coil. During the heating process pressure in the storage tank will gradually be built up.

The advantages of the system are:
1) The circulating pump needs only to overcome friction losses in the pipeline because the collector loop remains full.
2) A full flow of pressurized hot water is assured at all times.

The disadvantages of the system are:
1) Quality of service water must be good enough to prevent any corrosion or excessive deposits in the storage tank.
2) A pressurized storage tank is required.

 

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