Gece soğutmasının bina ısıl performansına etkilerinin saatlik analiz programı ile incelenmesi
Investigation of the effects of night cooling on building thermal performance with hourly analysis program
Yazar: İSMAİL ÇELİK
Danışman: DR. ÖĞR. ÜYESİ MURAT ÇAKAN
İstanbul Teknik Üniversitesi / Enerji Enstitüsü / Enerji Bilim ve Teknoloji Ana Bilim Dalı / Enerji Bilim ve Teknoloji Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Enerji = Energy ; Makine Mühendisliği = Mechanical Engineering

Özet:
Özellikle iklimlendirme alanında ihtiyaç duyulan enerji talebindeki artış, ısıtma ve soğutma sistemlerinde yeni arayışlara yol açmış ve enerji verimli sistemlerin tercih edilmesini sağlamıştır. Pasif yaklaşımlar, iklimlendirme sistemlerinde verimliliği arttıran önemli başlıklardandır. Gece soğutması ya da diğer bir tabir ile gece havalandırması, pasif ve fan takviyesi ile hibrit sistem olarak soğutmada enerji verimliliğini sağlayabilecek, enerji etkin bir sistem olarak karşımıza çıkmaktadır. Gece soğutması prensibi, temel olarak gün içerisinde yapıda biriken ısıyı gece dış ortam havası ile uzaklaştırmaya ve termal kütlede bu serinliği depolamaya dayanır.
Tez kapsamında gece soğutması örnek bir yapı ele alınarak saatlik ısıl performans analizine tabii tutulmuştur. Farklı iklim değerlerinin incelenmesi adına çöl iklimi, karasal iklim ve ılıman iklim bölgelerinden 4 farklı lokasyon seçilmiştir. Ben Guerir (Fas) çöl iklimini, Ankara karasal iklimi, İstanbul ve İzmir ise ılıman iklimi temsil etmektedir. Her bir lokasyon için Mayıs – Ekim aylarında soğutma ihtiyacı ısıl konfor değerleri göz önünde bulundurularak saatlik olarak hesaplanmıştır. 
Isıl yük analizinde, "Heat Balance Method"dan türetilmiş olan "Transfer Fonksiyonu Metodu" kullanılmıştır. Transfer fonksiyonunda yapının her bir bileşeni ayrı ayrı hesaplanarak ısıl yükler bulunmaktadır. Transfer fonksiyonu yöntemi, ASHRAE tarafından kabul görmüş bir hesaplama yöntemidir. Binalarda ısıl performans analizleri uzun ve karmaşık basamaklara sahip olduğu için saatlik yük analizi yapabilen paket program Carrier HAP®  kullanılmıştır. Esas alınan bina programa tanımlanırken, gece soğutması sistemini oluşturacak şekilde program kurgusu oluşturulmuştur. Buna gore iklimlendirme sisteminin çalıştırılmadığı zaman olarak gece saatleri belirlenmiş ve sırasıyla 3, 5 ve 8 hava çevrimi mahalde tanımlanmıştır.
Hesaplamalarda örnek yapının salonu için 24:00 ile 7:00 saatleri arasında gece soğutması yapılacağı ön görülmüş ve iç ortam set değeri 24°C olarak kabul edilmiştir. Daha sonrasında konfor sıcaklığının gece soğutmasına etkisini görmek için mahal set değeri 27°C alınarak sonuçlar tartışılmıştır.
Daha önce yapılan gece soğutması çalışmalarına benzer olarak, gece gündüz sıcaklık farkının fazla olması, gece soğutmasının verimliliğini arttırdığı saptanmıştır. Ben Guerir gibi çöl iklimine sahip bölgelerde gece soğutmasının yüksek verim ile çalıştığı, öte yandan yüksek sıcaklıkların gözlemlendiği mevsimlerde kontrollü gece soğutmasının yapılması gerektiği, karasal iklim bölgelerinde geçiş mevsiminde sıcaklıkların istemsiz olarak konfor sıcaklıklarının çok altına inebileceği, ılıman bölgelerde gece soğutmasının etkilerinin azaldığı ve nem gibi farklı parametrelerin de kontrol edilmesi gerektiği sonucuna varılmıştır. Sistemin verimlilğini daha iyi anlamak adına ısı pompasının COP değerlerindeki değişim de hesaba katılarak yapılacak olan yıl boyu analizler ileriki araştırmalara konu olabilir.

Abstract:
Energy demand in manufacturing, housing, transportation and in many other topic keep increasing from the past to present. Especially, changing in life style affects this situation. The comfort level of the people is one of the essential topic for buildings nowadays. Therefore, climatization systems are huge energy consumer in building sector. When different climate zones are oberserved, it is noticed that the demand and type of the energy ( heating or cooling ) are changing. Hot and mild climates zones generally require more energy for cooling and northern countries which have cold and continental climate require more heating energy. On the other hand, design approaches have been changed and now even cold climate zones demand cooling energy during certain time of periods. That's why cooling energy decrement in buildings with energy efficient systems would be key aspect for energy saving.
Energy usage in buildings is supplied by mostly fossil fuels. Decreasing the demand provide local and global benefits. Low demand means low energy supply and it leads to limited number of power plants. At the end, cleaner nature and rational orientated investments create difference in all around the world. Therefore building energy performance regulations are  considered as an important constituent in energys savings. These regulations for buildings are mostly about building façade, HVAC systems, lighting and sanitar systems. Standards such as ASHRAE, EN can be considered as an example.
Wise use of passive, active and hybrid system in buildings provide energy efficiency. Night cooling, also known as night purge and night ventilation, is considered as passive system. The main principle of the night cooling is based to swipe out abosbed heat during the day in the building components and store the cool by using cool night air. This method provides decreasing peak temperature and cooling energy demand during the day. The main subject in night cooling is the building should allow to store heat during the day and extract it by night that has lower outside temperature. Night cooling can be wind driven or it can be maintained with a fan. Additionally, due to unexpected temperature changes during cooling season may affect night cooling efficiency and makes it difficult to provide indoor comfort level.
Climate characteristic is the first topic to investigate for the night cooling because the night cooling performs at best for  low night temperatures come after hot and dry day time regarding to high temperature difference. Therefore, desert, semi-desert, continenal climate zones perform high efficient night cooling in general. One other topic is precipitation. In the location which considered for night cooling, precauitons should be taken both safety and humidity reasons. Automation systems help to sustain night cooling in controlling temperature and humidity interior spaces.
One of the main objective of the night cooling is to help indoor enviromental quality. Thermal comfort terms are defined by ASHRAE and ISO regarding to inside, outside temperature, clothing, activation levels and etc. It is claimed that in naturally ventilated spaces, occupants desire comfort levels with longer band gaps.
Passive cooling strategy night cooling has been researched regarding to many topics. Indoor air quality efficiency, evaporative cooling assistance, working with radiant cooling are discussed based on night cooling. These numerical and experimental studies helped to understand night cooling and determine parameters such as building physic, climate and etc. It is seen that mean outside temperature range gives clear understanding about climate affect in night cooling. It is also noted HVAC systems can provide night cooling with automation system with no additional investment and save significant cooling energy. Degree-days climate datas have been used to create a method to evaluate night cooling in Europe also it is asserted phase change materials can increse night cooling efficiency. 
Energy simulation is used to find out energy demand of building, selecetion of mechanical systems and energy utilization costs. Weather data, load profiles, constrction materials, equipment efficiency are need to perform simulation analysis. Heating and cooling energy demand of the building can be determined with simulation. To practise simulation, software programmes can be used to decrease the time spent for calculations. 
The calculations for cooling load of the building can be practise with different methods such as Heat Balance Method or Transfer Function Method. For each method, it can be said that heat gain occurs in space with convection and radiation. The solar radiation hits to surface of the wall and wall absorbe some amount of it and then release the rest. The surface temperature increases after absorbing radiation. If there is thermal balance between wall and indoor space, heat transfer starts from outer surface to interior. 
Heat load calculation can be complicated. Heat Balance Method is presented by ASHRAE and it is one the most complicated and accurate analysis method for building energy performance analysis. On the other hand, because of the complexity, much more faster and reliable methods as Heat Balance Method are taken in use such as Transfer Function Method. Transfer Function method assumes three principle. Total heating load equals to sum of each heat gain component and it is called superposition principle. Linearity principle says that the thermal response to heat gain change linear regarding to heat load maginitude. Uniformity principle means, the equal heat gains in different times create the same thermal response in the same. Based on these principles, Transfer Function Method is performed with two steps; find the transfer function coefficient and determine heat gains with time series. 
Energy simulation regarding to Transfer Function Method help to see night cooling performance in buildings. The night cooling and its efficiency for building energy performance are investigated with hourly analysis programme in the scope of the thesis. Different locations are taken to compare climate zones. Ben Guerir (Morrocco) represents dessert climate, Ankara continental climate, Istanbul and Izmir represent mild and humid-mild climate. Weather data for Ben Guerir is 2017 real life data and for the rest programme library data has been taken. To analyze energy demand and usage sample building is considered. There would be no additional building thermal behaviour improvement. The time period is chosen May-October to create clear comparison performance behaviours.
The example building is a residential house with a courtyard for five people. The night cooling is taken in action for living space. Occupant, lighting, electrical equipment and activation profiles are considered based on residential house type. There would be no heat transfer from adjacent spaces. Heat transfer occurs from wall and roof mainly and occupant, electrical heat gain loads come from interior. The wall characteristic is taken from architectural project. The walls consist of composite soil based material with 0,3 W/mK  heat conduction coefficient and wood based insulation bamboo with 0,05 W/mK. The overall U value of the wall is 0,181 W/m^2 K. The roof  has wood panel, insulation and proofing layer with overall U value 0,118 W/m^2 K. 
The programme used for calculations is Carrier Hap® and it has huge usage in building construction sector. The scenerio for night cooling is set based on creating air change in a room 3, 5 and 8 times per hour betwen 24:00 – 7:00.
To identify benefit of night cooling, the air change of room is considered regardless to wind pressure. The heating and cooling system in the building is air sourced heat pump and two pipe fan coil system. After night cooling implementation electrical usage is changed and cost analysis have been made relating to utilization. 
As a result, it is seen that outside temperature difference between night and day time increased the efficiency of night cooling. Calculation shows that Ankara and Ben Guerir have the highest energy saving rates. On the other hand, in Ben Guerir, high temperature may cause unexpected temperature increasing in space and in Ankara cool seasons (May, October) can cause low indoor temperature which is not desired. Therefore automation system can be taken in action for optimasing the night ventilation. Izmir, because of the mild climate, night ventilation has homogenious efficiency and lower than the other locations. Also humidty should be taken as a drawback in Izmir. Istanbul has promising energy efficiency for night cooling. It performs homogenous efficiency to compare with Ankara and Ben Guerir because it has much more mild climate. Day time temperature is not as high as Ben Guerir and night time temperature is not as low as Ankara which allow Istanbul to have certain efficiency during cooling seasons.
Increasing comfort temperature is another aspect to increase night cooling efficiency. The room temperatures is increased from 24℃ to 27℃ for Ben Guerir and the night cooling efficiency is jump from 8 ACH, %18 - %43 to 8 ACH, %25 - %64. The efficiency improvement is occured due to higher temperature difference between outside and inside air temperature. In Ben Guerir warm months like April and special temperature changes during cooler seanson also allow night cooling application and it might increase yearly benefit of night cooling for desert climate areas.
Based on the calculation it can be claimed that it is not easy to warrant thermal comfort for a space during all day or begining of the usage yet it is highly efficient passive system to decrease energy demand for cooling. Beside residential houses, night cooling can be considered in big complex buildings which have HVAC system. The automation scenerio allows to create night cooling with HVAC system even in existing buildings. For future studies, heat pump COP changes can be integrated to the building energy performance simulations, year based benefit of night cooling and thermal comfort change effect be disscussed for different locations and climate zones.