Combined heat and power assists Guernsey Prison.

Opened in 1989, Guernsey prison is the only facility of its type on the island must be equipped to hold in-mates of varying ages and sentences. Providing accommodation for up to 134 prisoners, the site also provides primary care services, education programmes and workshops. As the prison is in operation 24 hours a day 365 days per year, there is a substantial hot water, heating and electricity demand.
A phased approach to upgrading the heating had been in operation for many years, with like for like oil boilers replacing older models. Eager to find a more energy efficiency solution, the prison contacted our Building Services Officer, who recommended the introduction of combined heat and power technology to work alongside the existing system and to supply the majority of hot water demand required throughout the year.
The selection of gas fired CHP and oil fired boilers gave the prison additional fuel security as well as benefiting from generating electricity to be used in the Prison. With favourable contract terms from the local gas company substantial savings in operational costs could be made.
In February 2017, two Viessmann Vitobloc CHP units were installed by Refrigeration and Controls Limited, each of which providing 39 kW in terms of heating and 20 kW of electricity. The two Vitobloc CHPs generate hot water at 75°C into a Viessmann Vitocell buffer system. The hot water from the two 1500 L Vitocells are fed back through the existing oil boilers to provide reliable heating and hot water. The two CHP units operate 14 hours per day during the electricity supplier’s normal tariff hours and not during the low rate tariff hours. The buffer vessels help to extend the heating benefit of the CHP units outside of the normal tariff rate period. Oil consumption has dropped substantially, and normal rate electricity imported from the local network has also dropped.
Our Building Services Officer commented, “The States of Guernsey Prison is a fully operational facility and hot water supply has to be available every day. The contractor managed the installation without disruption of the Prisons day to day routine. Viessmann have been very helpful and supportive in supplying a CHP product which we can use on the local LPG air gas mix. Their ability to supply CHP units off the shelf reduced the project procurement time by several months. Guernsey Gas Limited, the local gas supplier is also impressed with the quality and service offered by Viessmann. They are working with them to get their local staff trained in the long term servicing and maintenance of the CHP units.”
With the new system operating as expected, the prison will be on target to recover the cost of the installation in 4 years, whilst also reducing carbon emissions by 65 tonnes per year.

Project Details
Project year:   2017
2 x Vitobloc EM20 units
2 x Vitocell buffer vessels
Rates output:
2 x 20kW Combined heat and power units
Buffer vessels 2 x 1,500 litres
Location:        State of Guernsey Prison
Contractor:     RefCO Limited
Support:         Guernsey Gas Limited