EC, energy efficient building services

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1 Propeller 22 Best practice examples of reduced power consumption in building services and refrigeration by integrated control of EC fans and motors. Author: Dr Simon Bradwell, Managing Director; ebmpapst Pty Ltd, 10 Oxford Rd, Laverton North, VIC 3026; Abstract The power consumption of building services and refrigeration can run to over 50% of total power consumption with buildings (1). Of this, a significant proportion is fan and motor applications in HVACR. This review will detail some examples of best practice solutions in the application of high efficiency EC fan technology and the benefits of speed control in achieving reduced power consumption and hence carbon emissions. Examples of integrated EC fan solutions show that 50% power savings can be achieved. Those discussed include: Increased efficiency in air conditioning applications with integrated remote site monitoring. Constant pressure and constant volume ventilation control systems for greater efficiency and easier commissioning. Improved energy efficiency and COP in refrigeration circuits

2 Propeller 22 Introduction Power consumption in fan motors has been estimated to consume 35% of all power in commercial office buildings and up to 60% in commercial supermarkets. Low efficiency fans and motors are used in: Refrigerating our soft drinks Ventilating our rooms Supplying air conditioned environments in our office Controlling our humidity Rejecting our heat load Cooling our computers and data centres Creating air curtains In 2003 ebm-papst and Gert Haeussermann realised the first fully integrated EC high efficiency fan for ventilation purposes. Now 60% of ebm-papst globally turn over of 1.3b Euro is made up of high efficiency EC fans and motors. DC motors and drives have been used in the automotive market for many years cooling radiators or actuating mechanical solutions. Traditional DC motors are inherently power efficient but commonly unreliable due to the carbon brush method of commutation. New Electronic Commutation (EC) or EC technology has brought together high efficient DC motors, Figure 1, with electrical commutation and integrated speed control, Figure 2, providing a greater than 90% motor efficiency motor. Due to the reduction in internal temperatures resultant of this efficiency increase, life times can double in comparison to some AC, lower efficiency, air movement products used in building service applications. Figure 1: The variation of motor efficiency [%] for EC, 3 phase, single phase and shaded pole motors with shaft power [W]. 2

3 Figure 2: An EC motor showing DC rotor, electronic commutation, power conversion and speed control electronics In the development of electronics to convert alternating current supply to direct current supply, many other features were made available. The two main features being: Integrated PID Speed control with the use of 0-10V or PWM supplies EC fans and motors can be controlled over 100% of their speed without the loss of efficiency. Integrated communication protocols RS485 connections allows remote site control and monitoring. This subsequently encourages both response based, proactive maintenance (i.e. a failing or aging system can be identified prior to failure and subsequent system failure) as well as fine tuning of equipment by remote site, dynamic balancing of building service systems. Speed control is a significant variable allowing building users to reduce power consumption. According to fan laws, power consumption is proportional to speed to the power three i.e. Pa = k.(n) 3 Where Pa = power absorbed [W] K = control factor n = speed [rpm] As shown in Figure 3, a 20% reduction in air volume can approximately halve power consumption; note for a given system, air volume is proportional to speed. Figure 3 also shows the variation in k factor applicable with various speed control techniques. 3

4 Propeller 22 Here, it is shown that as EC technology approaches the theoretical third power relations set out by the fan laws, all other speed control techniques have inherent losses in their methodology. For instance at the same duty point inverter control techniques typically absorb 36% more power than EC and triac control systems consume 118% more. Figure 3: The effect of speed control on the power consumption of fans using various control techniques. 4 Figure 4: The integration of EC systems into building services systems.

5 Integration of EC systems into Modbus or other communication protocols is shown in Figure 4. RS485 outputs from EC fans is used to feedback speed and performance data as well as fault finding and fault history. This allows fine tuning of the fan systems to be achieved as well as performance monitoring for maintenance. This ensures peak system efficiency for the maximum time. Best practice of EC in air-conditioning and refrigeration EC, high efficiency is applicable within the refrigeration circuit in both the cold or supply and hot or heat rejection circuits. Best practice in supply systems can utilise a range of both axial and centrifugal fan technologies dependant upon the system requirements. EC technology is widely used in evaporator circuits due to the double savings available due to the drop in heat rejected from the motor. The most widely used applied is in domestic or commercial refrigerators as will be highlighted subsequently. Supply side air-conditioning Some best practice examples in roof top (RTU) and air handling (AHU) packages as detailed by Lockwood (2) are shown in Figure 5. By changing the 15inch by 15inch forward curve belt driven fan and applying the backward curved, plug fan EC technology as detailed, it was shown that the fan power reduced from 6.3kW to 2.78kW. Although the improvement of COP has not been detailed publicly by the end user supermarket, it is anticipated that over the over 10 year life time of the plant, the improvements and savings were considerable. Condensers Giles (3) has explored the savings available using high efficiency EC condensers. Figure 5: Best practice example of EC plug fans to AHUs and RTUs. (after Lockwood) 5

6 Propeller 22 EC fans used in condenser applications can range in sizes from 450mm to 910mm. A massive reduction in energy requirement can be achieved in two ways; firstly by improvements of specific fan power and secondly by allowing floating head condensing pressure control as shown by Kroger (4). An analysis of the performance of EC condensers is shown below in Figure 6 by Giles (3). In this graph it can be seen how the noise, refrigeration performance, power and control features of the fan vary with each other. The fan speed is controlled by a simple 0-10V control from the refrigeration or air-conditioning controller and the fan feeds back its performance into the refrigeration controller via a tacho or rs485 feedback loop. Legend Constant TD ( K) Variable: Fan speed, control voltage, sound level, air quality, heat rejection (kw), condenser fan power (kw). Condenser Fan Power Curoe: Use this to establish fan power from the duty point. Constant: Heat Rejection Capacity (kw) Variable: Fan speed, control voltage, sound level, air quality, T.D., condenser fan power(kw). Constant: Fan speed, control voltage, sound level, air quality, condenser fan power (kw). Variable: T.D., heat rejection capacity (kw). Figure 6: The EC fan and the EC condenser 6

7 This clearly shows the reduction in power consumption and noise available with EC condenser fans. If we look at the temperature charts for Melbourne shown below, Figure 7, the normal design temperature of an ambient of 30degC is only attained for 2% of the hours in a year. From the above chart of EC condenser performance, even if the fans were used at 80% speed on average throughout the year then 50% savings can be made. This is a massive overestimation of the performance requirement but let us translate that to power and carbon savings. Temperature bin hours Melbourne Ambient temperature Cum h/yr from 20 degrees Hours per year per bin. Figure 7: Temperature Bin table for Melbourne % The recent survey of the refrigeration and Air conditioning market by Anderson (5) has surveyed the power consumed by this market sector. Below, in Figure 8, is shown the analysis of power consumption and savings available in translating the condensers to EC condensers in cold rooms. A similar calculation can be shown for air-conditioning. Description Total Power abs [GWh/a] COP Cool Rooms - (Data from CC-Coolrooms) HRF Heat Rejection [GW] Condenser air Qty [Gl/s] AC [W/l/s] AC condenser fan [GW] EC [W/l/s] EC condenser fan [GW] Deli Case/Other Retail 395,097, ,382,839, ,859, ,115, ,343,457 Mini (up to 3m x 3m) 65,594, ,582,080 27,038, ,652, ,029,954 Small (up to 6m x 4m x 3m) 86,338, ,184,960 35,588, ,388, ,253,102 Medium (6m x 6m x 4m) 100,915, ,203,200 41,597, ,311, ,815,314 Large (10m x10m x 4m) 152,494, ,729,280 62,858, ,114, ,343,141 Warehouse (20m x 10m x 4m) 201,830, ,406,400 83,194, ,622, ,630,628 Distribution Centre 607,173, ,125,105, ,277, ,088, ,072,140 1,609,443,264 5,633,051, ,414, ,292, ,487,736 % of total power consumption 13% 11% Figure 8: Estimated power consumed in Cool Rooms in Australia after Cold Hard Facts Anderson (5),

8 Propeller 22 Using the temperature bin data we can thus estimate the power and carbon savings achievable with EC condensers in Australia; these are shown below, Figure 9. EC condenser fans Savings 100% load 80% load 50% load Coldroon [GWhr] 39,804, ,978, ,694,561 GHG [tonne CO2] 52,940, ,172, ,643,766 Air-conditioning [kw] 601,116 1,872,276 2,789,179 GHG [tonne CO2] 799 2,490 3,709 Total GHG [MtonneCO2] 52, , ,647 Figure 9: Power and Green House Gas (GHG) savings with EC condenser fans Changing from AC to EC condenser fans is a simple process as proven by existing users. A speed control line is required but not to have a controller in modern refrigeration circuits is very rare and therefore the application of the EC technology is easy. The total savings available with EC condensers is 185,000 TWhr power savings or Green House Gas savings of 245,000 Mtonne CO2. This is a major contributor to Green House Gas targeted savings. Best practice of EC in ventilation systems It is common for central ventilation systems to use motorised, backward curved impellers, as shown in Figure 10, as these are by nature more fitting to Australian systems. The use of EC backward curved impellers is now becoming more common as, in combination with pressure monitoring controllers, required ventilation rates can be specified and maintained irrespective of the number of exhaust vents that are open. In order for the rooms to ventilate at the regulated required rate, the ventilation fan must operate against a known and constant back pressure. Commonly axial fans are used to ventilate apartments and therefore back pressure control is paramount as axial fan performance is particularly sensitive to changes in pressure. Traditionally a central ventilation unit is specified for the maximum pressure required when all the bathroom fans are discharging into the central system. The fan runs giving this pressure at all times irrespective of the number of exhaust units operating and therefore the system is never balanced. With EC however, the central ventilation unit can be controlled by measuring pressure in the central system as a differential against atmosphere. The design pressure at maximum ventilation is calculated at the design stages and then this is set in the controller (shown in Figure 11) at commissioning with all the exhaust systems in the building running. In Figure 10 a physical example of an apartment building lay out is shown with room ventilation systems discharging into a central system. 8

9 Typically individual exhaust systems in an apartment building operate at varying times of the day dependant upon the occupants. Therefore there will be varying number of axial fans pressurising the central riser at any one time. Using EC, this pressure variation is sensed and the EC fan is reduced in speed maintaining the constant pressure in the system, as shown in Figure 11. This in turn ensures the correct ventilation rates in each room. By controlling the ventilation system as its design pressure then the optimum control is obtained. This means that during periods of non occupancy, the central ventilation system will reduce in fan speed, as shown in Figure 11. As outlined previously, typically 50% power savings is available with EC when speed is reduced by 20% - i.e. if 20% of the occupants go to work in the day and turn off their ventilations systems approximately 50% power savings will be achieved. Figure 10: The application of EC in a central ventilation system 9

10 Propeller 22 Figure 11: EC control in a central ventilation system Best practice of EC in refrigeration and cooling circuits In refrigerated cabinets existing shaded pole motors are replaced by single core EC fans. The reduction in energy requirement and improvement in COP is shown in Figure Energy requirement [kwh] M40045-CA03-51 SAVING W1G200-EA Time [years]

11 Product Yearly savings per $ 0.12 Ø kwh System COP AC Q-motor $58.66 $48.88 $47.40 $46.77 EC W1G % 122% 119% 116% Figure 12: An EC fan for refrigerators and its use therein In a 12 month period the power savings per fan is 30W or kwh assuming the fans run 24/7. This corresponds to 352kg of carbon per year. It is reasonable to consider the population of shaded pole motors in commercial refrigerators in Australia to be in excess of 150,000. This would suggest that minimum savings of 38,000 tonne of Green House Gas (Carbon Dioxide) can be affected. If improved COPs are also factored in as shown in the Table then further improvement of 16-47% can also be realized on this figure. Conclusion It has been shown that power consumption in buildings is significant enough for innovation to be applied. The use of EC fan systems based on high efficiency direct current supply is a high efficiency motor solution. Integrated PID speed control features available in the ebm-papst EC fans, allows near fan law control of power consumption. Examples of best practice use of high efficient fans include the replacement of belt driven forward curve fans systems with EC backward curve plug fans in air-conditioning units; integrated EC condensers lower specific fan power and allow floating head pressure control; constant volume control of ventilation systems allows tuning of ventilation power consumption to occupancy rates massive reduction of fan power in fridges with subsequent improvements of COP. 1 The carbon produced per kwhr for brown coal is 1.33Kg CO2 for 1 kwh of electricity in VIC; ref: 11

12 ebm-papst Australia Pty Ltd VICTORIA 10 Oxford Road Laverton North VIC 3026 Phone Fax QUEENSLAND NEW SOUTH WALES Phone Fax SOUTH AUSTRALIA AND WESTERN AUSTRALIA Phone Fax NEW ZEALAND Phone Fax Please add me to the ebm-papst Propeller newsletter mailing list. Propeller 22 Integration of EC fans into internet and electronic communication networks is simple and remote site monitoring and effective reactive maintenance without system failure is simple to achieve. References: 1. Atkinson M: Building a better Climate Solution; Fin Review 22 July Lockwood G: Energy savings by improved application of fans in Air Handling unit: IMechE Events Publications, International Conference on Fans, 9-10 November Giles D; The magic of EC condensers; Propeller 21, internal publication, ebm-papst Pty Ltd, Kroger T: Heat reclaim v floating condensing pressure; Celsius, Jan 2003, p16 5. Anderson S; Cold Hard Facts The Refrigeration and Air Conditioning Industry in Australia; Australian government, Dept of Env and Water and Resources; June Name Position Company Name Address Postcode Telephone Please Post Mail 12