The guideline document finalised in the framework of the programme, as already stated, defines the basic general requirements to be fulfilled by the solar DHW projects. Based on that, the technicians responsible for the compilation of the call for tenders can define the specific obligations for a given project and, then, simply adapt the “Standard Technical Specifications” document to the jail needs.
The basic principles behind the technical specifications adopted for the completion of the programme (Table 1) are the followings:
1. The quality of the products, of the plant design and installation and the qualification of the installers are considered crucial for successful projects.
2. Multiple design choices are allowed whenever they fulfil the quality issues.
3. The annual energy to be supplied by the solar thermal plant is the main requirement. The plant size is implicitly defined by the expected output and may vary for different collector types and/or system configurations.
4. A Guaranteed Solar Results contract jointly with an appropriate maintenance procedure are expected to ensure the reliability of the system in operation.
5. Monitoring is considered crucial in order to detect possible areas of improvement.
6. Precautions against the proliferation of the legionella bacteria are especially addressed.
Last, but not least, possibilities for energy savings on the demand side could be preliminary detected and integrated into the solar thermal plant design.
Due to similar operating conditions, the design and installation criteria identified for a solar DHW plant in a jail can be easily extended to other public large DHW consumers.
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Table 1. Examples of the specifications for the implementation of a solar DHW plant in a j ail in the framework
of the Solar Jails Program.
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Topic
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Sub-system
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Requirements
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Solar system size
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• Not based on a pre-defined collector area (measured in m2 or in number of collectors to be installed)
• Based on the estimated annual solar output calculated as a fraction (lower than 70%) of the annual DHW energy demand
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Solar thermal collectors
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• Any type allowed among flat-plates and evacuated tubes.
• Fulfilment of the EN 12975-1 requirements and testing according to EN 12975-2
• Guaranteed at least for 5 years
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Other
components of the solar system
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Solar heat storage
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• V/S factor between 50 and 90 l/m2 (Jails usually have continuous DHW demand
• Minimum insulation thickness required according the Italian normative DPR 412/93
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Expansion vessel
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• Installation on the return piping in a way that the expansion vessel cannot be excluded by the non-return valve
• Formulas and assumptions to calculate the minimum expansion volume are given
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Heat exchangers
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• Temperature difference AT < 10 K
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Pumps
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• Electric power, required to run the pumps, low in comparison to the thermal power delivered by the solar field (1%)
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Solar system hydraulics
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• Any system hydraulics allowed (i. e. low -, high-flow) whenever the planned collector mass flow comply with the values reported by the manufacturer
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Solar collectors installation
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• Any tilt angle allowed. Only for flat-plates: tilt angle Ф horizontal. (Esthetical constraints are not applicable in jails)
• Any orientation allowed in the southern quadrant
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Water hygiene measures
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• Two separated circuits — the first, where solar heat is produced stored and, the second, where the DHW is produced and distributed — are required
• Pre-treatment of the water used to fill the solar storage tanks
• Enforcement of measures recommended by the Italian guidelines for the prevention of the legionella bacteria proliferation
• Whenever the DHW storage tanks are constantly maintained at 60°C, it is also required a distribution temperature of 53°C (max. distribution temperature allowed by the Italian normative DPR 412/93)
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Solar system performance
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• A guarantee of solar results is issued. A simplified formula for the calculation of the minimum annual energy output expected by the solar system is given that accounts for the irradiation and the heat demand in real operating conditions. The parameters required to adjust the estimated production must be measured and elaborated by the monitoring system.
• A plan for the maintenance activities is required
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Monitoring
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• Recommendations on the sensors positioning; on the parameters and quantities to be elaborated; on the equipments for data acquisition and storing are given. Simplified functional schemes where the measurement points are highlighted are given
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Designers and installers
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• Previous experiences on solar plants for big energy consumers are required
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2.3 First results
