How to save costs from recycled heat
37TWhr of heat energy are consumed from UK food processing and 11m tonnes of carbon dioxide is released in the atmosphere as a result1. Much of the energy is of low-grade and both complex and costly to recover, particularly at the point of rejection. By using recycled heat you can save costs of your water heating.
Food processes require continual heating and cooling, so if high-grade energy can be re cycled on a continuous basis there will be a return on investment.
The refrigeration condensing process presents such an opportunity to capture high-grade energy before the point of rejection. Once captured the source of high-grade heat, ie >70OC, may be used for heating water for food processing, for steam generation or for utensil and surfaces cleaning.
FSL helped a factory operated by Pork Farms group with a study on just how much heat and fuel (gas) they could save from their refrigeration condensers and quantified the saving in terms of CO2 tonnage.
The factory operated on a continuous 6-day, 2 or 3-shift pattern cleaning the production lines and processing equipment during the night shift between 10pm to 6am.
The reasoning behind the decision to recover heat was as follows:-
- Demand for hot water was high and reasonably predictable.
- The refrigeration plant rejected heat energy on a continuous basis.
- Water storage space close to the refrigeration plant was available.
FSL proposed the installation of a new heat recovery vessel in series with the common refrigerant condensing circuit from five Sabroe ‘open ‘compressors.
Heat recovered from the operation of the refrigeration plant provided a 5,000-litre store of hot water at 45-48OC to pre heat water for the hygiene shift.
For safety, a pipework bypass allowed isolation of the heat recovery vessel from the refrigeration circuit in the unlikely event of a fault.
An initial investment of £32,000 was projected for the heat recovery system. Additional cost was required to complete the water pipe work infrastructure connecting with the boiler hot well. (This was excluded from the calculation)
The estimated payback for the installation was achieved over a 2.5 to 3 year period based on gas savings at the prevailing price provided by Pork Farms.
Implementation of the system reduced the Carbon Footprint of the site by about 90 tonnes of carbon per year.
1 The Carbon Trust, 2010 figure.