Mitton Environmental Case Studies
CO2 Controlled Ventilation System
Demand controlled ventilation is a recent development in HVAC energy saving and control. Instead of a fixed rate of air being forced mechanically into a building by a constantly running fan, the CO2 levels in a building’s internal environment are monitored and then used to determine the output of the ventilation system.
Inverter controlled ventilation systems lend themselves to this technology very well. The ability to constantly vary fan outputs from a very low level mean they can balance the CO2 being produced by the occupants with the fresh air ventilation requirements. In addition, they will maintain an acceptable environment in the building without constant on/off switching, which is potentially wearing and damaging to components of more traditionally controlled systems.
In this installation, three individual CO2 sensors were installed at three different points in the building, allowing the average concentration of CO2 throughout the building to be used to determine the output of the air handling units.
The benefits were twofold. Firstly, the reduced output of the air handling unit resulted in immediate and measurable reductions in power consumption. Secondly, during the winter months these reduced outputs will mean less cool air being dragged in from outside the building, therefore reducing demands on the heating systems.
Current indications show a reduction of 88% in AHU electrical consumption, with no detrimental effects on interior temperature levels. Expected energy savings in winter months will be in the order of 40%, with maintained low interior CO2 levels giving scope for further energy savings. Carbon credits will also be saved, further improving payback.
Lighting Control System - Warehousing Complex
At an 18 year old grocery warehouse, Mitton was commissioned to carry out a detailed survey to report on potential reductions in consumed energy. The site had a high base load with minimal fluctuation, demonstrating a slight peak through the working day, dropping slightly at weekends.
The Mitton Environmental team identified a significant dip in base load corresponding to public holidays when the warehouse was closed and the internal lighting system was turned off.
Although a rudimentary lighting control system was installed in the main warehouse, this had a manual override. Tests and evaluations indicated that lighting could be reduced down by at least a third and probably two thirds, with the installation of lighting control to all areas lit by high pressure sodium lighting offered significant potential savings.
At peak daylight availability, this equated to a saving of 30% of building energy consumption.
Mitton recommended a three-way route to the client:
- The ‘free win’ approach, with staff educated to switch off lights when not required
- The maintenance/low cost approach of changing existing light fittings for modern HF light fittings and implementing a system of roof light cleaning
- Installation of a full lighting control system
The client opted for the full lighting control system. This was carried out at a total cost of £18,000, and full payback was achieved in less than six months.
Combined Heat and Power System - Morrisons Supermarkets
Although Combined Heat & Power systems were first installed over 20 years ago, today’s high performance equipment can yield efficiencies of over 80% and, when correctly implemented, can dramatically reduce energy overheads. In today’s climate, this can bring the user advantages in the shape of government incentives including climate change levy relief and enhanced capital allowances, further improving the impact on energy bills.
In line with Morrisons’ ongoing strategy of energy conservation and reductions in carbon emissions, Mitton has installed an Ener-G Combined Heat and Power (CHP) unit at the company’s supermarket in Thornbury, Bradford, to allow evaluation of the potential contribution of this technology.
The system installed at Thornbury produces 150kW of electrical power and around 231kW of heat, consuming the equivalent of 474kW of gas. Under full load, this produces an efficiency of 80.4%.
It uses a gas converted diesel engine to drive a three phase 415v 150kW generator, which is integrated into the store’s electrical systems. Heat generated by the engine is then removed by passing through heat exchangers on the coolant systems, oil coolers and exhausts, thus giving a direct supply of heat to the store’s main heating systems.
The exhaust heat exchanger effectively demonstrates the potential power of these CHP systems. Initial tests demonstrated that exhaust temperatures, measured at over 650oC on leaving the engine, dropped to 109oC having passed through the exchangers, giving a remarkable level of heat recovery.
Data so far points to a very successful integration with the existing power and heating systems, with only a negligible increase in exterior noise levels. The payback scenario is at best case 3.16 years, and at worst case 5.3 years, yielding annual carbon savings up to 190 tonnes. The system is being monitored continuously to determine best quality operational parameters.
Morrisons Supermarkets were recently awarded the new Carbon Trust Standard recognising the organisation’s commitment to reducing its carbon footprint throughout the business. This Award has been presented to only 12 organisations in the country, and only one food retailer, giving Morrisons a significant lead in the industry.