case studies 2013 - nhs sustainability day · during a building inspection, a variable speed drive...
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Case Studies Overview The Case Studies outlined in this document represent a number of projects that have been identified and implemented by Low Carbon UK, over the last 18 months. All of these give an outline of different initiatives that we have implemented in respect of plant improvement and optimisation. The Cost Savings stated within each Case Study are actual savings identified from measurements taken before and after implementation of each initiative. 1. Chilled Water Plant Optimisation ‐ Demand Logic 2. Air Handling Units (AHUs) ‐ Time Schedules 3. Fume Cupboard and AHU Optimisation 4. Heating Control Modifications 5. AHU Fan Replacement 6. Close Control on Computer Room Air Conditioning (CRAC) Units 7. Chilled Water Pumps ‐ Controlled Improvements 8. Ventilation Heat Recovery ‐ Run‐around Coils 9. Fan Modulation ‐ Variable Speed Drives (VSDs) 10. Calorifiers to Plate Heat Exchangers (PHXs) 11. Insulate Plate Heat Exchangers (PHXs) 12. Thermostatic to Electronic Expansion Valve Upgrade 13. Low Carbon UK’s Chiller Optimisation Method 14. Installation of Liquid Pressure Amplification (LPA) 15. Lighting and Lighting Controls Upgrades
T 01903 215731 W www.lowCO2.eu
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Site overview Four storey office building located in close proximity to Gatwick Airport. The Problem During an audit of the BMS controls function, it was discovered that the chilled water plant (rated at 250kW input power) was being triggered by a fixed‐time regime and that frequently, the chilled water plant was being enabled when no demand existed. The principle observation that confirmed this was a very minor temperature differential between the flow and return temperatures that was mainly attributable to pipework losses, rather than actual plant demand. A review of the software revealed that the only interlock present was a low‐ambient hold off setting.
The Solution The software control was modified to include demand logic from Fan Coil Units (FCUs) and Air Handling Units (AHUs). It was established through the monitoring and normalisation of electricity consumption that this enhancement of the software resulted in an 8% reduction in the chilled water electrical load over the year.
Case Study: 1
Chilled Water Plant Optimisation—Demand Logic
Measurement of Savings Achieved Annual Energy Reduction = 55,000kWh Annual CO2 Reduction = 30 tonnes Annual Cost saving = £4,400 Cost of implementation = £1,500 Return on Investment Payback period = 4 months
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Site overview Three storey office accommodation for large banking group in Colchester. The Problem During an energy audit of this building, it was observed that the two primary AHUs were being enabled three hours a day, prior to general occupation of the offices. The software was back engineered and the cause was located as an error in the software. The AHUs were being triggered by the optimum start function, rather than the fixed‐time start trigger.
The Solution The software triggering the AHUs was modified to use the fixed‐time trigger. Based on the additional run hours and the motor sizes the saving was calculated at £6,000 per year giving a return on investment of one month.
This calculation did not include the additional energy saving associated with the AHU process (Low Pressure Hot Water (LPHW) and Chilled Water (CHW) usage within the AHU and the additional load on the heating systems).
Case Study: 2
Air Handling Units (AHUs) ‐ Time Schedules
Measurement of Savings Achieved Annual Energy Reduction = 75,000kWh Annual CO2 Reduction = 41 tonnes Annual Cost saving = £6,000 Cost of implementation = £500 Return on Investment Payback period = 1 month
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Site overview Laboratory building accommodating laboratory and write‐up areas in East Kent. The Problem The air change rate for laboratory supply and fume cupboard extract remained constant at 24 air changes per hour.
Each of the supply and extract fans had been previously fitted with a Variable Speed Drives (VSDs) however, they were running at fixed speeds to provide a laboratory to corridor pressure differential of 15 Pascals.
The Solution A “sash‐close” regime was instigated within the laboratories, allowing the air volume to be reduced for each of the air systems at night. Air volumes were measured by way of a Pitot traverse and a night‐setback required volume was calculated taking account of the laboratory’s specification. The software was then modified to allow this enhanced functionality. Much of this work had to be undertaken “out of hours”; consequently, the return on investment was calculated at 9 months. This calculation has been based on the reduction of fan power however, it does not include the additional energy savings associated with the conditioning of treated spaces.
Case Study: 3
Fume Cupboard and AHU Optimisation
Measurement of Savings Achieved Annual Energy Reduction = 350,000kWh Annual CO2 Reduction = 192 tonnes Annual Cost saving = £28,000 Cost of implementation = £21,000 Return on Investment Payback period = 9 months
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Site overview A newly built Adult Learning Centre in Croydon. The Problem The building design included a ground source heat pump coupled to thermostatically controlled, zoned under‐floor heating systems. Two small industrial boilers had also been installed to provide LPHW supplying radiators for perimeter heating. A review of both systems suggested that the heating activity in the building was mainly being done by the Low Pressure Hot Water (LPHW) system. All of the radiators were found to have their Thermostatic Radiator Valves (TRVs) turned to maximum. The TRVs had been turned to maximum, whilst a fault with the under‐floor heating system was being corrected. However, the TRVs were never returned to their previous setting.
The Solution All radiator TRVs were turned down from the maximum setting to a setting of 19°C; then subsequently fixed to prevent tampering. The software trigger for both systems was modified to create a “dead band”, so that the under‐floor system was enabled before the LPHW radiator system, whereby the perimeter heating system was used as a back up, rather than the primary source of heating within the building. The theoretical return on investment on this modification was calculated to be in the region of four months. The actual measurement of the savings established through the analysis of site consumption data (from utility metering) however, was under two months.
Case Study: 4
Heating Control Modifications
Measurement of Savings Achieved Annual Energy Reduction = 150,000kWh Annual CO2 Reduction = 28 tonnes Annual Cost saving = £3,000 Cost of implementation = £500 Return on Investment Payback period = 2 months
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Site overview A large university campus building in East Sussex. The Problem During an energy audit of this building, the existing AHU fans were found to be predominately belt‐driven, potentially resulting in a 5‐15% transmission loss and requiring regular maintenance. All fan units were found to have old technology fan systems installed i.e. forward or backward curved fan, resulting in low efficiency. On measurement of fan absorbed power, it was established that all AHUs were operating on poor part load efficiency and power factor.
The Solution High‐efficiency, backward curved impellers were installed to replace existing fans, providing 38% efficiency savings that was achievable at matched duty The new fans were directly driven to eliminate transmission losses, which also led to the reduction of maintenance costs. Optimum‐sized motors were specified to take advantage of full load efficiency and power factor and hence, to abolish the need to fit frequency inverters.
Before
After
Case Study: 5
AHU Fan Replacement
Measurement of Savings Achieved Annual Energy Reduction = 51,500kWh Annual CO2 Reduction = 18.8 tonnes Annual Cost saving = £4,120 Cost of implementation = £8,250 Return on Investment Payback period = 24 Months
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Site overview Data centre located in Gloucestershire. The Problem On inspection of existing CRAC units, it was established that these units were fitted with old technology, low‐efficiency, forward curved fans. The existing belt driven fans resulted in the requirement for regular maintenance and cleaning of plenums to minimise the belt dust ingress into servers, which, according to our research, costs in the region of £5,000 per 1,000m2 annually.
The Solution High‐efficiency, directly driven fans were installed and optimised to provide efficient and effective air flow to the treated space. Fans installed were fitted with integral electronically commutated (EC) motors therefore, eliminating magnetising losses and hence, increasing overall efficiency. The fans installed featured Integrated Speed Control, which were set up and commissioned on a temperature control regime for optimum efficiency.
Case Study: 6
Close Control on Computer Room Air Conditioning (CRAC) Units
Measurement of Savings Achieved Annual Energy Reduction = 38,000kWh Annual CO2 Reduction = 13.7 tonnes Annual Cost saving = £2,990 (per unit) Cost of implementation = £4,650 (per unit) Return on Investment Payback period = 19 Months
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Site overview An NHS Trust in Berkshire.
The Problem During a building inspection, a Variable Speed Drive (VSD) fitted to a Low Temperature Hot Water (LWHW) pump motor was found to be operating to a constant speed regardless of demand. The pump was operating at 47Hz and drawing 9.5kW at the time of the inspection.
The Solution Rather than operate at static speed, this pump was set up to make the best use of the inverter installed, which was based on a pressure regime and interlocked using an AHU cooling valve feedback loop, thus taking account of cooling valve operation and modulating the pump accordingly. This strategy ensured that, when there was no demand for cooling and all modulating valves were closed, the pump was set back to a minimum frequency of 15Hz. The modification of this control strategy realised an overall energy saving of 45% annually, when compared to the previous static control.
Case Study: 7
Chilled Water Pumps – Control Improvements
Measurement of Savings Achieved Annual Energy Reduction = 37,500kWh Annual CO2 Reduction = 20 tonnes Annual Cost saving = £3,000 Cost of implementation = £1,000 Return on Investment Payback period = 4 Months
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Case Study: 8
Ventilation Heat Recovery ‐ Run‐around Coils
Measurement of Savings Achieved (AHU 3) Annual Energy Reduction = 305,000kWh Annual CO2 Reduction = 57 tonnes Annual Cost saving = £6,100 Cost of implementation = £4,250 Return on Investment Payback period = 8 Months
Site overview Large MoD site in Edinburgh. The Problem The majority of Air Handling Plant (AHU)s were once through‐systems with no heat reclaim. This example demonstrates savings on a single AHU No. 3.
The Solution Low Carbon UK were commissioned to design and install a number of run‐around coils on AHUs, which would result in the effective reclaim of exhaust heat and thus, reduce energy savings across the site. Appropriate modelling software was used during this process to establish the scope of savings achievable prior to installation, which were subsequently verified using appropriate heat meters.
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Case Study: 9
Fan Modulation ‐ Variable Speed Drives (VSDs)
Site overview An acute hospital located in North of England. The Problem Whilst undertaking an energy audit of this site, and the subsequent analysis of fan curves and Pitot traverse measurements, it was established that there was a significant over‐supply of ventilation by the maternity block general Air Handling Unit (AHU).
The Solution Subsequently, through our recommendations, variable speed drives (VSDs) were fitted to supply and extract AHU fan motors and modulated to provide a suitable air change rate for the area being served. This resulted in a change of frequency from 50Hz to 38Hz whereby the amount of absorbed power consumed by ventilation plant was significantly reduced.
Measurement of Savings Achieved Annual Energy Reduction = 113,880kWh Annual CO2 Reduction = 63 tonnes Annual Cost saving = £6,833 Cost of implementation = £6,000 Return on Investment Payback period = 11 Months
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Case Study: 10
Calorifiers to Plate Heat Exchangers (PHXs)
Site overview A large university in the West Midlands.
The Problem On review of this site’s domestic hot water (DHW) system, we identified that the current set up consisted of a number of inefficient, un‐lagged calorifiers requiring high maintenance, a regular legionella prevention regime, as well as annual pressure testing.
The Solution
In order to reduce maintenance costs and increase DHW system efficiency, a project was initiated whereby a number of DHW calorifiers were replaced with PHXs.
The decision to undertake this work was supported by prior research (through the use of heat meters), whereby it was established that the heat‐transfer efficiency of PHXs is typically 90%, compared to similar tests carried out on calorifiers which consumed substantially more energy, typically operating at about 60% efficiency, primarily due to storage losses and system pasteurisation requirements.
A 30% improvement in efficiency can therefore be realised on hot water generation through the use of PHXs.
Other benefits of using PHXs over calorifiers are:
Increasing the capacity is easy (simply by adding more plates).
Low water content reduces the risk of legionella breeding.
Compact for installing in tight spaces.
Easy to install and maintain (the plates simply unbolt and can be removed).
Calculating savings prior to this installation were based on 25% of total site gas consumption (that being utilised for DHW generation), which equates to 8MWh per annum (100% calorifier utilisation operating at 60% efficiency compared to 100% PHX utilisation running at 90% efficiency).
Annual cost savings illustrated do not take account of savings associated with the reduced maintenance and testing requirements of a plate heat PHX DHW system.
Measurement of Savings Achieved Annual Energy Reduction = 2.4MWh Annual CO2 Reduction = 556 tonnes Annual Cost saving = £48,000 Cost of implementation = £190,000 Return on Investment Payback period = 48 months
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Case Study: 11
Insulate Plate Heat Exchangers (PHXs)
Site overview A London Museum. The Problem A modular steam PHX serving the constant temperature heating circuit was found to be uninsulated, resulting in thermal losses to the plant area. Assumptions Plate Heat Exchanger Size 1m2
Fuel Cost per kW £0.02 Operating Temp (°C) 82 Operating Hrs p.a. 8,760 Emissions Unlagged 900 W/m2 Emissions Lagged 70 W/m2 Cost of Jacket £420.00 Estimated Savings p.a. £145.00 Estimated Payback Period 36 Months
The Solution Based on a number of assumptions (see left), the installation of an insulating jacket would reduce heat losses from the system and contribute toward an overall reduction in energy consumption. The heat loss calculation is based upon an insulated PHX in comparison to an uninsulated PHX as per energy efficiency office recommendations. Fitting an insulation jacket on nine uninsulated PHXs across the site is anticipated to realise annual savings in the region of £145 (per PHX) and will pay back in 36 months. Whilst a 36 month payback is anticipated when insulating a hot water to hot water PHX, payback periods are likely to be halved on steam to hot water systems.
Measurement of Savings Achieved (for nine 1m2 PHXs) Annual Energy Reduction = 65,000kWh Annual CO2 Reduction = 12 tonnes Annual Cost saving = £1,305 Cost of implementation = £3,780 Return on Investment Payback period = 36 Months
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Case Study: 12
Thermostatic to Electronic Expansion Valve Upgrade
Site overview A large commercial building located in London. The Problem A thorough analysis was undertaken to ascertain chiller performance at this site, whereby it was identified that excessive levels of super‐heat was evident from the outlet of the chiller evaporator coils. It was recommended that electronic expansion valves be considered, in order to improve efficiency. Existing set up
Measurement of Savings Achieved Annual Energy Reduction = 40,000kWh Annual CO2 Reduction = 22 tonnes Annual Cost saving = £3,200 Cost of implementation = £5,500 Return on Investment Payback period = 20 months Expansion valves fitted
The Solution Electronic expansion valves were installed on two 254kW chillers at this site. In addition, head pressure on these chillers were modified from fixed to floating head pressure control on both systems to improve condensing efficiency. In order to establish savings potential resulting from this installation, the electronic expansion valves were fitted in parallel with the existing thermostatic expansion valve and operation was switched between the two systems, three times per week to allow a fair comparison to be made. Energy savings were achieved with the electronic expansion valve because lower levels of superheat out of the evaporator allows better heat transfer and hence, higher evaporating pressures to be used. The energy savings achieved through this installation were measured over a two month period and on average, were found to provide approximately 9% savings with increased savings in warmer months.
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Overview A data centre located in London. The Problem There was a general concern at this site regarding the efficiency of operation of six large water chillers (collectively having a rated output capacity of 2MW). One of the difficulties of operating in the energy optimisation field is knowing the condition of equipment before you start work. The Solution The advantage of Low Carbon UKs optimisation method is that there is no need to install flow meters and that it provides a detailed chiller analysis within 30 minutes, without reliance on pre‐installed devices; it also provides better field accuracy at much lower cost than traditional methods.
The advantages obtained from this site were: COP increased from 3.0 to 4.0 Discharge Temperature reduced from 80°C to 58°C Superheat reduced from 11K – 16K to 6K Risk of failure reduced substantially
The outcome of our analysis and subsequent control changes resulted in a 16% reduction in power compared to the previous years trends (after normalisation). In addition, our method measures a chillers actual COP and other vital parameters which indicate whether the system is operating within tolerances and whether or not equipment has been effectively serviced.
Case Study: 13
Low Carbon UK’s Chiller Optimisation Method
Measurement of Savings Achieved Annual Energy Reduction = 520,000kWh Annual CO2 Reduction = 286 tonnes Annual Cost saving = £41,600 Cost of implementation = £10,500 Return on Investment Payback period = 3 months
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Overview A large manufacturing site in the West Midlands The Problem During a survey of the main process water chiller at this site it was noted that the existing position of the evaporators were 8 meters above the receiver. This required a relatively high head pressures to be maintained which was achieved through the use of a number of air‐cooled condenser fans. Refrigerant ‘flash gas’ (the partial re‐evaporation of condensed liquid refrigerant in the liquid line) was evident at the time of survey indicating a loss of system efficiency. The Solution Appropriate system pressures were effectively achieved by installing LPA pumps in the liquid lines between the condenser and evaporators.
The pumps increased the pressure in the liquid line to overcome losses in the pipework which allowed compressor discharge pressures, and in effect temperatures, to be reduced, thus reducing chiller compressor power. Following the modifications, the system now operates at a low head pressure. However, as condenser control is far more critical when operating at low head pressure, an inverter was installed on each condenser to control the fans. These are now operated simultaneously and their speed is modulated to provide accurate pressure control. With LPA, for much of the year condensing temperature can be floated to 5‐15°C above ambient temperatures. This ability to control head pressure is the most significant area of cost savings. The optimum pressure was calculated and adjusted dependant on compressor loading and ambient temperature. The measured energy saving resulting for these modifications was 32%. The issue of ‘flash gas’ was also overcome through the use of the LPA pumps.
Case Study: 14
Installation of Liquid Pressure Amplification (LPA)
Measurement of Savings Achieved Annual Energy Reduction = 150,000kWh Annual CO2 Reduction = 82 tonnes Annual Cost saving = £12,500 Cost of implementation = £10,000 Return on Investment Payback period = 10 months
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Overview A food manufacturing site in Tiptree, Essex. The Problem During a energy survey of this site it was evident that a significant proportion of the electrical building load was attributed to lighting. This facility was made up of several open plan manufacturing areas artificially lit by way of a number of energy intensive (400W) metal halide lamps. All non‐manufacturing areas such as offices, storage spaces and other ancillary areas were lit using T12 and T8 fluorescent fittings that incorporated magnetic ballasts; no lighting controls were installed, which resulted in many lamps being unnecessary illuminated when areas were either unoccupied or day lighting levels were adequate.
The Solution A lighting upgrade was initiated whereby all T12 and T8 fluorescent fittings were replaced with high efficiency T5 tubes and electronic control gear. In addition, all old inefficient metal halide units were replaced with energy efficient, high bay induction lamps. Effective lighting controls were also designed and installed to complement the new energy efficient luminaries; these included technologies such as PIR occupancy sensors, light level sensors (photo cells) and long range microwave sensors.
Case Study: 15
Lighting and Lighting Controls Upgrades
Measurement of Savings Achieved Annual Energy Reduction = 284,348kWh Annual CO2 Reduction = 2 tonnes Annual Cost saving = £18,482 Cost of implementation = £41,694 Return on Investment Payback period = 27 months