School Cooling

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Guide to School Cooling Resources for school energy managers Cooling can present a substantial energy cost to schools. Temperatures of 24° to 27° with less than 60% C C relative humidity give acceptable comfort in summer. Higher temperatures can be considered comfortable with air movement created by a breeze or a fan. Schools located in northern Victoria may need cooling systems to maintain a comfortable working environment. Careful consideration should be given to the use of natural and passive
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    Guide to School Cooling Resources for school energy managers Cooling can present a substantial energy cost to schools. Temperatures of 24°C to 27°C with less than 60% relative humidity give acceptable comfort in summer. Higher temperatures can be considered comfortable with air movement created by a breeze or a fan. Schools located in northern Victoria may need cooling systems to maintain a comfortable working environment. Careful consideration should be given to the use of natural and passive methods of cooling before the installationof electrically powered cooling systems in schools. It is more efficient and effective to stop heat entering a buildingrather than having to remove heat to lower internal temperatures. Heat entry into your school can be reduced by:  Insulation to ceilings (and walls if possible);  External shading to north, east and west windows. Insulation reduces heat transfer through walls and ceilings.Shading awnings and shutters reduce radiant heatpassing through windows As significant heat in summer enters through windows,external shading and insulation are important strategiesin keeping schools cool.As well as providing shade, trees and shrubs plantednext to buildings provide a cooling effect through leaftranspiration. The leaves give up moisture, whichevaporates and cools the air in the immediate area.Watering should be done in the evening to avoid leaf-scorch and mulching will help retain soil moisture. From School Cooling, Ministry of Education (Schools Division)Victoria, 1986. Reproduced with permission of theDepartment of Education, Employment and Training (DE&T).    ENERGY EFFICIENT COOLING STRATEGIES Minimise the heat entering buildings by:  shading of north-facing windows with deciduous trees, shade cloth, external blinds or awnings;  closing internal curtains or blinds during the day;  fully or partially covering east and west-facing windows with notice boards or providing external shading;  applying white gloss paint to metal roof surfaces. This can reduce internal summer temperatures by up to4–5°C; and  applying reflective films to windows to reduce glare and heat transfer. These films have the disadvantageof reducing natural light and solar heating in cooler months. Effectiveness of various window treatments  * Effectiveness is reduced as the colour darkens.ã Solar film, tinted glass and reflective glass of varying effectiveness is available. They significantly reduce light levels all year round. Remove heat from rooms by:  opening doors and windows when outside air is cooler in the morning to delay the need to switch oncoolers;  venting rooms at night with secure ceiling vents or high windows;  utilising cross flow ventilation;  using ceiling fans to increase air circulation. Running costs are only about 2 cents per hour; and  many central heating fans can be operated during summer to increase room ventilation, or purge rooms ofheat at night..    Where mechanical cooling is installed:  set thermostat no lower than 25°C in summer (every extra 1°C adds 10% to energy consumption);  rooms with refrigerative air conditioners should have doors and windows shut;  open doors or windows to discharge air from evaporative coolers;  maintenance is important! Regularly clean filters on air conditioners and maintain drive belts andthermostats in good working condition;  if the condenser coil of a refrigerative air conditioner is exposed to direct sunlight, provide shading andweather protection, but don't restrict movement of air around it;  limit access to after hours use of air conditioning, particularly if the system is centralised serving the wholeschool. Arrange for the cleaners to begin work as soon as classes finish;  evaporative cooling outlets should be closed off during cool weather; and  power points supplying small room air conditioners can have a push button time delay switch fitted toensure they aren't inadvertently left running when not required. MECHANICAL COOLING Fans Fans produce a cooling effect by moving air over the skin,encouraging moisture on the skin to evaporate which, in turn, causesthe skin to cool. Although they do not reduce actual roomtemperatures or humidity levels, fans can often provide an adequatelevel of comfort and provide the cheapest method of cooling.Ceiling fans should have a head clearance of 600–900 mm for safety. They can be suspended with down rods inareas with high ceilings. Note the following:  the number of blades has no effect on cooling capability. Metal blades are best;  units should be mounted clear of existing light fittings to avoid annoying flicker;  they should have a reverse spin setting to assist with winter heating; and  general classrooms require two ceiling fans.Purchase cost: $60–$200 eachRunning cost: 2 cents* per hour *Based on a assumed electricity tariff of peak rate 16c/kWh and natural gas tariff of 95c/MJ. AIR CONDITIONING The installation of cooling systems can substantially increase energy costs for schools. There are two mainoptions available to schools—evaporative cooling or refrigerative air conditioning. Schools should consider theissues below when considering these systems.Prior to installing cooling systems, careful consideration should be given to passive methods of cooling, especiallyshading and ventilation. Even if a school intends to pursue mechanical cooling, the adoption of passive coolingmeasures will reduce the energy use and operating cost of cooling or air conditioning systems. There are severalimportant differences between evaporative and refrigerative systems including operation, performance, ventilation,running costs, and peak electrical demand.    Evaporative coolers Evaporative coolers draw warm outside air through a series of wet filter pads. As the water evaporates in this airstream, it is cooled and becomes more humid. Dust is also filtered. The cooled air is blown into the building,cooling rooms as it passes out through open windows, doors or vents.To work effectively, it is vital that rooms filled with evaporative coolers have adequate ventilation to exhaust airoutside. They are an excellent cooling choice in most buildings, provided some doors and windows can be leftopen during school hours or adequate vents can be installed. Evaporative coolers are significantly cheaper tooperate than refrigerative air conditioning. Performance limitations  The main disadvantage of evaporative cooling is its reduced performance during humid weather conditions. Thehigher the humidity level, the less evaporation takes place, and the less cooling can be provided by the system. Innorthern Victoria these days are rare, but in Melbourne the number of such days per year is usually between 5and 10. However, the system should work well on most hot school days over summer.On humid days it may be more appropriate to use evaporative systems in ‘fan-only’ mode, which provides asteady flow of air through the room. The air movement will still assist local cooling of the skin.Evaporative systems are not as sensitive to the level of insulation because they continuously blow cooled airthrough the open doors and windows of a room. Sizing  Evaporative coolers are rated according to the volume of air they can move through a room. This is usually quotedin litres/second or cubic metres/hour. An evaporative cooler should be able to change the whole volume of airenclosed in a room 35 times every hour. Installation  Evaporative coolers are usually installed on the roof and deliver cooled air directly into rooms through a dropperduct. Sometimes multiple ducts from a larger unit are used to cool more than one room.
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