Designing Cooling &
Heating Systems

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FSL was commissioned by R Twining & Co. Ltd to provide a report, audit and survey to determine the heating and cooling demand for their Andover site.

The primary reasons for obtaining the information were,

For the selection of new high-efficiency water heating boilers.
As a study into the benefits of generating both power and heat on site. (CHP)
To benchmark site heating efficiency against established industry standards.

FSL recorded all the heating devices on site. Heating was provided to offices and the factory by circulating hot water in pipe work around the factory and offices to various terminal-heating devices.

The total heat demand required the calculation and summation of all heat outputs from the heating devices (many of which were aging) with the appropriate adjustments for water entering temperature.

Similarly the air conditioning loads were calculated using industry standard load data.

The brief excluded assessment of the heating gain as a result of the thermal properties of the building structure, the effects of aspect, internal and solar heat gains and occupancy levels.

Air conditioning by direct expansion refrigeration was provided for some offices; a future study would show if modification to chilled water-cooling to all offices could be achieved.

The audit showed that the office heating demand was approximately 200kW. The factory heating demand was approximately 900kW. In addition, the cooling load for all the offices was found to be approximately 400kW.

FSL explained how local power generation combined with heating saved money by operating at greater efficiencies than the national power infrastructure and by reducing the tax levied on CO2 emissions.

FSL illustrated how CHP provided power and heating for the site base load and the remainder from existing or new conventional heating and cooling systems. These would operate in parallel with CHP to respond to exceptional peaks in demand.

While CHP provided heat energy as a by-product throughout the year, FSL emphasised the importance of full utilisation to deliver the optimum payback for the investment.

Ideally, FSL proposed, the factory process-heating load absorbed the majority of the energy output. The remainder was used, for instance, to provide a source of chilled water using an absorption chiller.

This type of chiller was inefficient and if operated from a primary heat source delivered a negative energy return. If the heat supplied was ‘free’ from a CHP installation it allowed the absorption chilling to have a return on capital cost.

Using the chilled water for cooling buildings or processes during hotter months was a consideration. If not, options to sell the energy to others or to reject the excess heat to atmosphere would remain. This reduced the return on the initial investment.

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