The University of Leeds is recognised internationally for the excellence of its teaching and research. Leeds currently has over 33,000 students from 142 countries, and over 7,600 members of staff.
As a socially responsible organisation and research-intensive University, Leeds looks to lead the way in reducing its impact upon the environment and wider society. The Universities Carbon Management Plan defines desired outcomes, actions and targets to support the ambitious aims of the University. The plan aims to reduce carbon emissions from buildings, owned vehicles, and waste and water by 35% by 2020, compared against the 2005/06 carbon emissions baseline.
The University has invested heavily in sub metering and monitoring and targeting systems and as a result of this investment we are able to quantify and demonstrate carbon savings made by investing in targeted energy reduction schemes. For this submission we have chosen to highlight a number of particularly successful energy reduction schemes, a small sample of the many schemes that the University has undertaken since the adoption of the 2011 Carbon Management Plan.
Chemistry Teaching Laboratory Fume Cupboard Refurbishment
The 765m2 Joseph Priestley laboratory situated in the Chemistry building provides students with the opportunity to perform inorganic and organic chemistry practical work in an industry standard environment and reflects the research-led approach to learning and teaching within the School. It has 63 fume cupboards, with 55 being used for students on a regular basis during term time, the remaining 8 used for permanent apparatus, and overnight reactions. It can accommodate a maximum of 104 students at any one time, including students with disabilities.
£345,000 was spent upgrading 63 constant volume fume cupboards in the 765m2 Priestley Chemistry Teaching Laboratory to low energy variable air volume cupboards
The intention of the project was to reduce the thermal and electrical energy use due to the high ventilation requirements of the teaching laboratory. The scheme involved the reduction of fume cupboard face velocity from +0.5m/s to 0.4 m/s; following SF6 containment testing at the lower velocity by an independent specialist. In addition the extraction rate for each cupboard was linked to sash height so that a constant air face velocity was maintained with the air volume reducing through the use of motorised dampers and external bleed dampers whilst ensuring compliance with environmental and fume cupboard European standards.
A specially designed low volume fume cupboard for disabled access was installed as part of the scheme and all of the remaining cupboards were re-engineered to remove air bypass paths and promote laminar flow.
Further energy savings were made by altering the existing ductwork system and installation of a completely new, fully independent, extraction system for the end of isle and under cupboard chemical storage cupboards. This work has made it possible to fully shut down the 63 fume cupboards, the associated supply and extract system and the large fume dilution system outside of normal teaching periods; general laboratory ventilation being provided via the new solvent extract system.
New enhanced controllers were retrofitted to each cupboard and a “Modbus” communications network installed to enable remote monitoring of each cupboards sash height, face velocity and air volume via the Universities building management system. The latter being used to control the supply air volume provided by the two roof mounted air handling units in conjunction with room mounted differential pressure sensors.
Due to the sporadic nature of the fume cupboard usage and following discussions with the laboratory staff it was decided to install a key switch function which would enable the staff to activate the cupboards in banks of eight. This function enables the staff to select the appropriate number of cupboards to match the class size or to operate a limited number of dedicated cupboards for extended experiment periods.
As a significant proportion of the identified energy savings relied upon students closing fume cupboard sashes, when not working at the cupboard, each fume cupboard was fitted with a PIR motion detector and appropriate sash position sensing device. These devices provide an audible sash open alarm whenever the operator moves away from the cupboard for a predetermined length of time without first lowering the sash, the time being agreed in consultation with the lab manager. The audible alarm not only saves energy but also promotes good sash behaviour from the beginning of the student’s laboratory experience.
Savings and Benefits
A 6 month reduction of conditioned air thermal energy of 1647 MWh/Year compared to previous years consumption over a similar period (data normalised against standard degree days). The change in profile can be seen in Figure 1 with the 6 month data highlighted in orange.
The scheme raised awareness amongst staff and students of fume cupboard operational costs and in particular the role they can play in reducing costs it also encouraged a behavioural change in use of fume cupboard sashes resulting in safer and more energy efficient operation.
The scheme also produced a quieter and more comfortable working environment due to the reduction in supply and extract air volumes.
A 6 month reduction in Building Wing level electrical energy of 347MWh. From the electrical energy consumption bar chart, Figure 2, the step change in energy following completion of the scheme use can be observed.
Overall a 6 month combined (electrical and thermal) reduction in energy costs of £81,217.00 + VAT; indicating that the scheme was on course to payback within 2-3 years. 511 tonnes of carbon were saved over the 6 month period September 2013 to February 2013.
In the 2 years since completion the scheme has averaged annual electrical savings of 480,000kWh, equating to £40,000 per annum and 220 tonnes carbon, due to a refurbishment programme steam consumption for this period is incomplete.
Garstang Server Room Evaporative Cooling System
Following an approach from the Faculty of Biological Sciences for advice/assistance regarding an energy efficient replacement for an R22 40kW air conditioning system, cooling a critical server room, the Engineering Services team developed a proposal for the installation of an evaporative cooling solution. The proposed solution would provide similar performance to the existing system but use a fraction of the energy without the use of refrigerant and compressors. The total cost of the project was £36,000 including VAT, and on completion immediately reduced cooling related energy consumption by 90%’, equating to a saving of approx. £9000 per annum and carbon emission reduction of 50 tonnes CO2.
The existing air conditioning load was provided by an N+1 arrangement so we were able to remove one of the air conditioning units whilst maintaining room conditions with the remaining unit.
The all air evaporative system required two 650x650mm ducts (supply and extract) to be routed from the plant room above into the server room, one duct terminating above the false ceiling, the other into the existing raised floor. Due to the size of the ducts access holes additional steel supports were added to re-inforce the floor slab.
To prevent dust contamination into the room a floor to ceiling enclosure was erected and carefully sealed before any of the construction work commenced.
A single EcoCooling ECPWB unit with heat recovery was installed providing the equivalent of 35kW of cooling, new floor grilles and temperature sensors were installed and an alarm link to the Trend BMS installed to warn of system failure or over temperature events. A flood warning system was installed with water solenoid shutoff incorporated into the units’ water supply pipe.
Savings and Benefits
Figure 3 below shows the immediate impact that the installation of the evaporative cooler had on energy consumption, energy consumption being reduced by over 90%. It can be seen from the associated table that energy consumption has gradually increased over the period 2014/15 this coincides with the installation of additional data capacity (additional cooling load) that was installed during this period.
With the energy heat recovery cycle we have been able to run the unit using free cooling for a significant portion of the year so water consumption for the unit has been minimal. The associated maintenance and repair costs have been very low @ £180 per annum, this combined with the removal of legislative requirements such as TM44 and F Gas regulations has significantly reduced on-going operating costs.
Figure 4 below shows how effective the evaporative cooling system is at controlling room temperature without significant affecting specific humidity levels.
North Precinct Summer Heat Loss Reduction Programme
The University of Leeds uses a 300mm high pressure steam distribution network to provide heating and hot water to the on campus academic and residential buildings. A survey by Ove Arup & Partners Ltd into the operation and feasibility of the system identified standing losses of 1300kw (thermal) per hour.
A survey of all steam supported services was undertaken and essential steam supplied services such as Autoclaves, catering equipment and high demand installations where identified. These installation were, in the main, close to the Generating Station Complex, the source of the steam supply, and although various alternative electric based solutions were considered these were found to be either not cost effective or not viable due to limited electrical capacity local to the load. Through the installation of additional isolation valves and a package of works to systems higher up the system we developed a solution that would enable a significant proportion of the steam main to be isolated during low demand periods, whilst maintaining steam to the essential services. It was estimated that reducing the length of the operational steam main over the summer months could result in savings of approx. 1,898,000kWhth per annum.
Funding of £170K was obtained from Salix via the Revolving Green Fund to undertake the work required to enable the steam main to be isolated, a payback of 3 years was identified for the scheme with carbon savings of 351 tonnes per annum anticipated.
The project work was completed Sept 2015 and briefly involved undertaking the following measures to supplement existing systems
The installation of 3no additional Steam isolation valves at key points in the system.
The design and installation of thyristor controlled electrical re-heat batteries and resistive type humidifiers into 4no. close control supply air distribution systems, the addition of 8no. in-line electric immersion heaters to upgrade or introduce immersion heater back up to preexisting DHW services.
Control upgrades to five existing DHW immersion systems to enable remote switching and control of the whole DHW system via the Trend BMS system.
The schematic in Appendix 2 shows the scope of the full system, the sections coloured in yellow are those we were able to isolate following the enabling works described in this section
Savings and Benefits
The upper (yellow) section of the University steam distribution system was isolated on the 4th June 2016, figures 1&2 in Appendix 1 demonstrates the reduction in total steam consumption for the University main campus and the associated increase in electrical consumption resulting from the operation of the electrical back-up systems. The savings for June 2016 are summarised in table 1 below:
The overall carbon saving figure of 244 tonnes and £87,192 in June is significant. Going forward the intention is to formalise this strategy so that summer heat loads are, where feasible, satisfied by point of use electric systems. This system of operation relates well to the new operating strategy of the Generating Station Complex which will be operating on a heat demand basis rather than an electric demand basis. This means that with a lower summer heat demand the GSC will operate less generators and boilers and utilise spare grid capacity to satisfy demand.
Appendix 1 – Main Campus Energy Consumption
Appendix 2 – Steam Distribution Schematic