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Website: VENTILATION The need to ventilate The air renovation in the inhabited places is a physiological need. The breathing of the occupants is translated in a consumption of oxygen and an expulsion of carbonic gas. The lack of ventilation implies a decrease of the rate of oxygen, becoming the environmental air harmful for breathing. This decrease of oxygen is not the only factor that makes the air renovation necessary. Any activity in a house produces dampness. The own fact of breathing contributes a substantial quantity of water steam to the air, provoking an increase of the relative dampness and as consequence of it, the appearance of condensations, formation of mildews and deterioration of the finished ones. To avoid these problems is necessary to ventilate. A good ventilation will allow: - To contribute new air, necessary for the breathing. - The evacuation of smells and / or toxic gases. - To protect the housing of mildews and degradations due to the water steam. Ventilation system After a lot of research, we have decided to use an innovate solution which provides domestic houses the combination of natural ventilation and heat recovery, known as Passivent iHybrid. This solution provides the benefits of natural ventilation (a proven no-energy, highperformance and energy efficiency solution) and heat recovery (provides thermal comfort, reduces heat loss in cold weather and improved comfort). This iHybrid system is intelligent, that means it knows which mode it should operate in by using sensors to monitor the external temperature. When the external temperature is below 9ºC the system will switch the heat recovery fan on to operate in Heat Recovery Mode. The warm air being exhausted passes through the heat exchanger in the heat recovery unit. At the same time, the cold air which is being brought into the house passes through the heat exchanger. The heat is transferred to the incoming air to provide warm tempered air to the dwelling. Filters within the heat recovery unit ensure that unwanted pollutant do not enter the home. Doing that, a lot of advantages appear as energy efficiency, warm incoming air, reduced heating load requirement, fresh air, effective control of moisture and relative humidity, thermal comfort for occupants... On the other hand, when the external temperature is above 9ºC the system will switch the fan off and activate innovate damper technology which diverts the exhaust air through the ductwork used in Natural Mode. In this mode, ventilation is driven primarily by the natural stack or convection effect by which warm air rises, so no power is used during operation. Moisture-laden air is extracted directly from wet rooms (kitchens, bathrooms...) through ducting up to a roof terminal where it is vented to the outside. Wind blowing across the roof provides additional suction. Supply air is provided to the dwelling through temperature sensing wall vents. This provides free fresh air, effective control of moisture and relative humidity, low maintenance costs, automatic control, silent extraction... Combining both worlds, the Passivent iHybrid solutions provides low annual energy use, low annual running costs, lifetime cost savings, improved comfort, guaranteed ventilation, high levels of indoor air quality, efficient operation... Benefits ο· 55% electrical consumption saving against mechanical heat recovery. A temperature of 9ºC would be the optimum balance point within a dwelling. Based on this, it is calculated that the iHybrid system will operate in Heat Recovery Mode for approximately 45% of the year. As a result, 55% of the electrical energy of the fan would be saved as it would be switched off while operating in Natural Mode. ο· Less carbon emissions Calculation show that carbon emissions would be reduced by approximately 8.5% using the Passivent iHybrid system compared to a standard heat recovery system. This is because the standard system uses energy all year round to bring in fresh air. While Passivent iHybrid uses no energy for supply air while operating in Natural Mode. ο· Extended life expectancy and lower life cycle cistings As the iHybrid system will operate in Natural Model for 55% of the year, the heat recovery unit will be switched off for this time. It is estimated that this will prolong its expected life to approximately 20 years compared to 10 years for a standard mechanical heat recovery unit which will be working 100% of the time. In addition, filter changes will be required less frequently with the Passivent iHybrid system, as they are not used while the system operated in Natural mode. ο· Energy efficiency With a standard mechanical heat recovery system, a summer bypass will usually be used to bring air in from outside without passing over the heat exchanger. To do this the system is continuously using electrical energy. In contrast the Passivent iHybrid system uses no electrical energy in the summer to bring un fresh air when heat does not need to be recovered. Ventilation requirements Ventilation requirements for comfort: π= 10 β πΊ 1 β πΆπ β πΆπ ππ£ Where G is the pollution load, πΆπ is the desired perceived indoor air quality, πΆπ is the perceived outdoor air quality, and ππ£ is the effectiveness. The results are: ο· ο· ο· 2-bedroom house: π = 105πΏ/π = 0.105 π3 /π 3-bedroom house: π = 136 πΏ/π = 0.136 π3 /π 4-bedroom house: π = 180 πΏ/π = 0.180 π3 /π Power required πΉππ ππππ’π‘ πππ€ππ = πβπ π Where P is the pressure drop, V is the ventilation flow rate and πis the efficiency. The results are: ο· ο· ο· 2-bedroom house: πΉππ ππππ’π‘ πππ€ππ = 15π 3-bedroom house: πΉππ ππππ’π‘ πππ€ππ = 19.4π 4-bedroom house: πΉππ ππππ’π‘ πππ€ππ = 25.7π So, for the whole community: πππ‘ππ πππ πππ€ππ ππππ’π‘ = 6 β 15 + 10 β 19.4 + 4 β 25.7 = 386.8π When the external temperature is below 9ºC the system will switch the heat recovery fan on to operate in Heat Recovery Mode. Looking at the table for Ayrshire temperatures we can see there are 4 months were the temperature is always above 9ºC and 5 months were it is bellow 9ºC. April, May and October have temperatures higher and lower than that value. We will assume that approximately 50% of the time the fans are on. Total energy required in a year: πΈ = 363.8 β 8760 2 = 1593.44ππβ References http://www.passivent.com/ http://www.learn.londonmet.ac.uk/packages/clear/thermal/buildings/active_systems/mv/ind ex.html http://chestofbooks.com/home-improvement/repairs/Mechanics-Household/MechanicalVentilation.html http://www.eurocable.es/esp/productos/vm_duo_mecanico.php?h=2 http://www.conaif.es/dinamico/editor/vetilacion.pdf http://www.abe.psu.edu/extension/factsheets/g/G91.pdf