Heat Gain Study of a Residential Building in Hot-Dry Climatic Zone on Basis of Three Cooling Load Methods

The paper presents the study on theoretical heat gain for a residential building located in hot-dry climatic zone of India. The location is city Kota (25.100 N, 75.830 E). To determine heat gain, three different methods have been used. The aim of the paper is to study the heat gains and also to compare the three different methods. First method is CLTD/GLF method which is taken from ASHRAE 1997, second method is CLF/SCL/CLTD method which also taken from ASHRAE 1997 and third method is RLF method which is taken from ASHRAE 2013. After that comparative study has been done of all three methods. For the study a typical middle income group residential house has been considered. The model house is taken of size 12 m x 15 m with three windows of size 1 m x 1m each and one door of size 1 m x1.5 m. The walls are brick wall and roof is taken of RCC. From the analysis it is found that CLTD/GLF method predicts heat gain towards lower side whereas CLTD/SCL/CLF method values are higher and RLF values lies in between being more close to CLTD/SCL/CLF method. An important point to notice on comparison of results is that all methods predict around 50% heat gain through roof for this building structure. Another major contribution to heat gain (around 30%) is through walls. The window to wall ratio for the building is 1.9% and therefore the effect of heat gain through windows is only around 8%. Other factors contribute only a minor percentage to the overall heat gain. Thus, from the results it can be concluded that in order to reduce the heat gain and cooling load, major attention must be paid on roof and wall heat gain along with the other factors. Suitable passive measures can be identified on the basis of heat gain study.


I. INTRODUCTION
Heat gain of a building can occur through walls, roof, doors, floor and window glazing by conduction, convection and radiation.Heat gain mainly occurs due to direct exposure of building envelope by solar radiation.There are other reasons of heat gain also which include household kitchen equipments, electrical equipment like computer, TV, lighting devices, infiltration, ventilation and number of occupants in the building etc.Thus, heat gain may be classified as external heat gains and internal heat gains.Further, the heat gain can be also described as sensible heat gain and latent heat gain.Sensible heat gain is associated with temperature increase and may be due to conduction, convection and/or radiation in the space.Latent heat gain is associated with water vapor/moisture (phase change) and is Published on September 26, 2019.N. Sengar is with Department of Pure and Applied Physics, University of Kota, Kota, Rajasthan 324005 India.(e-mail: namrata@uok.ac.in).
A. Sharma is with Career Point University, Kota, Rajasthan.(e-mail: antima.sharma86@gmail.com)due to breathing of occupants, equipment, and ventilation/infiltration of air.
For a building to be comfortable for occupants without wastage of energy, it is important that heating and cooling loads are clearly estimated.Heating load for a building may be defined as the amount of heat required to be supplied to the building in order to maintain it in thermal comfort range.Similarly cooling load may be defined as the amount of heat which should be removed from the building in order to maintain it within thermally comfortable range.A number of studies have been conducted on heat gain and cooling load estimation.M.Gr.Vrachopoulos et al. presented the method for determining the thermal and cooling load in Athens.They evaluated density of building, size of cover, weight, volume and consumed energy [1].Cooling load of building can be determined if heat gain of building is known.S.L. Wong et al. determined the heat gain in Hong Kong and observed increasing trend in heat gain of building envelope.They analyzed from the study that the average annual cooling load in duration 2009-2100 can reach 6.1% and 9.85% which is greater than in duration Heat Gain Study of a Residential Building in Hot-Dry Climatic Zone on Basis of Three Cooling Load Methods Antima Sharma andNamrata Sengar 1979-2008 for low and medium forcing [2].By estimating heat gain of building over consumption of electricity for a particular space can be reduced because it gives an idea that how much electricity consumption is required for one place.It also prevents too much cooling and too heating of the place because some places require more energy and some places require less energy.Many studies have been done to decrease the cooling load of buildings.Mehdi Baneshi, Hiroki Gonome and Shigenao Maruyama discussed the cooling load of single stage single family home in three different climates and with different cool black paints.They observed a decrement in peak and annual cooling load by 6-13% and 6-14% respectively [3].Lighting load can be reduced by using fluorescent lamp in place of tungsten lamp.By 'make air tight and ventilate right' approach the cooling load can be decreased [4].Vinod Kumar Venkiteswarana, Jason Limana and Saqaff A. Alkaffa studied various passive measures for reducing cooling load including wall insulation by polystyrene, single lowemissivity window glazing and white painted roof, and compared the results.They found that wall insulation is the most effective method for Malaysian climate and also it is cost effective too [5].
To calculate heat gain due to lighting a simple lighting heat gain model is used in ASHRAE's new cooling load calculation [6].Deepak Kumar Yadav et al. determined cooling load in different climatic conditions using Cooling Load Temperature Difference (CLTD) method.A tutorial room was selected for the study [7].Eng.Essa S. Ben-Essa determined cooling load for one storey villa with basement located in Kuwait using CLTD method and discussed result [8].Felix A. and Emmanuel A. estimated cooling load of a building situated in Ghana using transfer function method (TFM) and then compared the result with the result of cooling load estimated by computer programme [9].Baisong Ninga,b, Youming Chena investigated a cooling load calculation model integrated operation of radiant and fresh air system.For that they used heat balance method.They also investigated cooling load calculation method using Chinese standard on radiant system [10].
Yu Wang et al. studied the effect of climate change on cooling load of residential building.They also studied the effect of climate change with respect to the age of the occupants.They observed that the climate change effect is more pronounced for people under the age of 55 [11].Yuanda Cheng et al. studied the different cooling load calculation methods used over 20 years and concentrated on STRAD system [12].E. Catalina Vallejo-Coral evaluated the CLTD values for flat roofs and walls of buildings for different climatic zones in Mexico.For this they used complex finite Fourier transform, then compared the result with ASHRAE CLTD values.They found 10 o C difference between them with the ASHRAE values on higher side [13].Anurag Kumar Singh et al. estimated heat gain for library in Delhi using CLTD/CLF method.The estimated heat gain for library came out to be 48614.91W [14]. M. D. Suziyana et al. calculated the heat gain of computer laboratory and an excellence centre using CLTD/CFL/SCL method.They obtained the heat gain values for computer laboratory and excellence rooms as 20458.6W and 33541.3W [15]. Hani H. Sait did hand calculation using CLTD method to determine thermal load of building and then results were compared with the outcomes from HAP 4.2 program [16].Wan Sharizatul Suraya W.M.Rashdi, Mohamed Rashid Embi investigated the relation between building design and cooling load for this they used computer simulation analysis program Autodesk Ecotect [17].G. Evola, L. Marletta used solar response factor to determine solar gain through glazing and compared the results with EnergyPlus [18] Heat gain for a building and cooling load are strongly interconnected.Cooling load is used to design a heating, ventilating and air conditioning (HVAC) system to remove heat from a space to provide a specified condition of thermal comfort within that space.Cooling load is directly dependent on the modes and amount of heat gain by various components of the building envelope and therefore cooling load calculations make use of estimation of heat gain.American Society of Heating, Refrigerating and Airconditioning Engineers (ASHRAE) have given various methods to determine cooling load on basis of heat gains such as A) CLTD/ GLF method B) CLTD/SCL/CLF method C) TETD/TA method D) TFM method F) RLF method

A. CLTD/ GLF method
This method is used to determine heat gain only for residential buildings.This method is very simple and one of the earliest method.In this method sensible gain is determined using cooling load temperature difference (CLTD) and glass load factor (GLF).Latent load is determined using latent factor with the help of psychometric chart.CLTD is a theoretical temperature difference used for estimating heat gain taking into account combined effects of the inside-outside air temperature difference, daily temperature and solar radiation variation and thermal mass of building.

B. Transfer Function Method (TFM)
In this method heat gain is determined using conduction transfer function coefficient and then heat gain is converted into cooling load using room transfer function coefficient.

C. CLTD/SCL/CLF method
In this method CLTD is used to determine external conduction gain and SCL (solar cooling load) is used to determine solar gain through glass.SCL is to be added for more accuracy.CLF (cooling load factor) is used to determine internal conduction gain.In this method hourly values of heat gain can be calculated by using hourly CLTD values.This method is modified form of TFM method.

D. Total Equivalent Temperature Difference/Time Averaging (TETD/TA)
In TETD method the TETD values are calculated as a function of sol air temp and maintained room temperature with the use of response factor technique.Here a number of representative wall and roof assemblies can be taken.The internal heat gain elements are added to it and after that time averaging technique is used to convert heat gain into cooling load but this can be solved only with help of computer due to its complexity.

E. Residential Load Factor (RLF)
In RLF method the procedure consists of two steps, in the first step the cooling load factor and heating load factor (CFs and HFs) are determined for each component then these factors are used to estimate cooling load in second step.The load contribution of various components is determined separately and then added.RLF is simple procedure which is hand manageable and can be used with spread sheet application [19].
Estimating heat gain and cooling load of a building is one of the most important steps towards better designing of a building in hot dry climatic zone.It helps in choosing measures which can lead to improvement in thermal comfort with optimized energy usage.For the present study Kota, a city situated in hot dry climatic zone of India has been chosen.This paper discusses the estimation of heat gain of a residential building of Kota through three different methods-CLTD/GLF method and CLTD/SCL/CLF method and RLF method.The aim is to develop an understanding of the heat gains due to various loads which can be used in subsequent studies to suggest measures for improved thermal performance of the building.It does not focus on designing of an HVAC system, the main aim is to improve design of buildings and identify feasible passive measures on the basis of this study.In the first section of the article, heat gain is determined by GLF method, in second section CLF method is used, after that in third section estimation is done by RLF method.The results with respect to various components of building and internal loads have been presented for all the three methods in form of tables.The three methods have been comparatively studied and the results have also been comparatively analyzed.

II. STRUCTURAL DETAILS OF A RESIDENTIAL BUILDING FOR KOTA
For studying the heat gains a single family detached house located at Kota (25.10 o N latitude) of dark color has been assumed.The construction and occupancy details are presented in Fig. 2 and table I.
The size of house is 15 m x 12 m which is usually owned by middle income group.Here it is assumed that the house contains two bedrooms, one kitchen, one living room, one bathroom and one storage room.The size of both bedrooms is 9x3 sq.

Outdoor design condition
Temperature of 41 0 C dry bulb with almost 13 K daily range and relative humidity is 30% with humidity ratio .0147kg/kg[21].

Indoor design condition
Temperature of 24 0 C dry bulb temperature and 50% relative humidity with humidity ratio .0092kg/kg.

Occupancy Four persons
The humidity ratio is taken from psychometric chart.It is assumed that the house has no overhang.The construction of the house is considered as medium.

III. ESTIMATION OF HEAT GAIN THROUGH CLTD/GLF METHOD
This method uses CLTD values to calculate heat gain through the opaque structure such as walls, roof and floor.Glass load factors are used to find heat gain through windows [22].Here following equations are used to find out the heat gain.

Glass and window areas 𝑞 = (𝐺𝐿𝐹)𝐴
(1) Above grade exterior walls  =   () (3) Partitions to unconditioned space  =   () (4) Ceiling and roofs  =   () Exposed floor  =   () Infiltration  = 1.2∆ ) Latent Factor (LF) 0.65+35*Ho ( U-factor for wall is taken from [20], GLF, CLTD for wall, roof and door and ACH are taken from [22]. Total cooling load = LF x (Sum of individual sensible cooling load components) (10) Where q = sensible cooling load(W) ∆t = design temperature difference between outside and inside air(K) A = area of applicable surface(m 2 ) U = U-factor for appropriate construction(W/m 2 K) Qfr = volumetric airflow rate(L/s) ACH = air change per hour(1/h) GLF = glass load factor(W/m 2 ) CLTD = cooling load temperature difference (K) LF = latent load multiplier Ho -outdoor design humidity ratio (vapor kg/dry air kg) Internal load due to people is assumed 67 W per person.The appliance and light load of 470 W is divided between the kitchen and adjoining room and the laundry and adjoining room.It is assumed that 50% of the kitchen appliances load is picked up in the living room.The infiltration is determined using (7) and (8).The heat gain through walls is determined using (3) and the heat gain through roof is determined using (5).The heat gain through window or glass area is determined using (1).GLF is selected for single glass glazing with no shade inside.The design temperature is taken 41 0 C.   Sensible heat gain due to ventilation q =1210xairflow∆t (11) Multiplying the number of people in the space by the .01m 3 /s of outdoor air required per person in the space Ventilation airflow = 4x0.01m 3 /s/person = 0.04 m 3 /s.The ventilation heat gain can be determined using equation (11) with airflow 0.04 m 3 /s and ∆t as 17 0 C. The value for sensible heat gain as a result of ventilation is q = 0.823 kW Thus total sensible heat gain = 31.66kW.The total heat gain is the sum of sensible and latent heat gain.The calculation for latent heat gain is shown below in form of latent cooling factor (L.F.).

IV. HEAT GAIN ESTIMATION THROUGH CLTD/SCL/CLF
In previous section the CLTD / GLF method is used to determine residential heat gain.This method is used for residential buildings only.Through CLTD/ SCL/CLF method both residential and nonresidential heat gain can be determined.In this section it is used to determine heat gain for the same residential building shown in Fig. 2. Following are the equations that are used to determine heat gain.
Conduction through roof, wall and glass Solar load through glass People   = ( ℎ ) ( 14) Ventilation and infiltration Corrected CLTD values ()  = () + (25.5 −   ) + (  − 29.44) Where SC-shading coefficient SCL-solar cooling load factor either considering no interior shade or with shade CLF-cooling load factor by hour occupancy Hooutdoor humidity ratio (from psychometric chart) Hi -indoor humidity ratio (from psychometric chart) Qv-ventilation /infiltration air flow (L/s) The CLTD value should be corrected according to location condition.Equation ( 18) and (19) shows the corrected value of CLTD.
In above expressions CLTD value for glass is taken from [23], CLTD values for wall and door are taken from reference [24], SCL values for glass is taken from [23], SC value is taken from [22], CLF value is taken [22] and it is taken 1 due to 24 hour occupancy, sensible heat gain and latent heat gain from people are taken for sitting and activity level related to very light work [22].
= (  ∆ +   +   ) = (∆ − 0.46 ) +  ×  ×  ×   (23)  =     ( unshaded fenestration) ( 24) = 0.05  + 3.5(  + 1) Where qopq= opaque surface cooling load(W) A = net surface area( m 2 ) CFopq = surface cooling factor (W/m 2 ) U = construction U-factor (W/m 2 .K) (for window it is taken from table 2  Table XVI shows the heat gain through opaque.OFt, OFb and OFr, values are taken for roof, ceiling assembly and CF is calculated using (21).Daily temperature range is taken as 13 K and heat gain through opaque surface is determined using (20).Table XVII shows the heat gain through fenestration.Fenestration is assumed of single glazing with wood frame.PXI is calculated from (24).SHGC is taken for single glazing wood frame window.IAC is taken 1 because it is assumed that there is no shade inside.FFs is taken for single family detached house.CF is calculated using (23).Heat gain is calculated using (22).Table XVIII shows the heat gain through infiltration.Aul is selected for averaged house.AL is determined using (28).IDF is taken for design temperature 40 0 C which is almost nearby 41 0 C. Qi is determined using (27).Qv is determined using (28).Qvi using (29).qvi,s is determined using (30).Table XIX shows internal heat gain.qig,s is determined using (31).qvi,l is determined using (32).qig.l is determined using (33) and ql is determined using (34).

VI. COMPARATIVE STUDY
A comparison of the relative points of difference and similarity between the three methods used in the previous sections is presented in form of table XXI for better understanding.
It can be seen from the table that in CLTD/GLF method the heat gain through walls and roof is calculated using CLTD values which are specified in tables, whereas in SCL method the specified CLTD value is corrected using (18) and (19).
In RLF method direction is not mentioned while calculating heat gain through wall.Heat gain is calculated for overall wall but in both previous methods heat gain is calculated separately according to direction.In RLF method OFt, OFb and OFr is specified.Same is the case for door.
For windows in GLF method the glass load factor includes both solar and conduction gain and is specified in form of tables.In SCL method conduction and solar gain are calculated separately for the windows.For conduction gain corrected CLTD values are used and for solar SCL values are used which are specified.In RLF method FFs and SHGC values are specified which are taken according to the type.
For occupants in GLF method occupant load is assumed 67 W per person while in SCL method and RLF method latent and sensible load are calculated separately for internal gain which includes occupants and appliances both.For appliances in GLF and SCL method appliances load is assumed 470 W.
In GLF method infiltration and ventilation is calculated separately.In SCL and RLF method sensible and latent load is calculated separately but includes both ventilation and infiltration.Both methods use same formula but in the SCL method the flow rate is assumed while in RLF method the flow rate is calculated.In GLF method latent factor is calculated separately.

VII. RESULTS AND DISCUSSION
Table II to VIII present the sensible gain estimation of residential building in Kota using CLTD/GLF method.This method selected one by one room for heat gain estimation.The sensible heat gain of building without ventilation load is 30.84 kW.The ventilation load in form of sensible heat gain is calculated separately and it is 0.823 kW.The latent factor of building is estimated using (9) and it is 1.16.The total heat gain is estimated using (10).The calculated total heat gain is 36.73kW.
Interesting point to observe from the results for heat gain through walls was that maximum heat gain is through east wall.The reason can be attributed to the fact that in the mornings when sun is on the east wall the temperature gradient is higher and as a result the conduction gain is more.From CLTD/GLF method heat gain cannot be calculated on hourly basis and this method is used only for residential building.The CLTD/SCL/CLF method can be used for both residential and non-residential building and heat gain per hour can be calculated.Similar observation regarding east wall can be seen from this method also.The tables (IX) to table (XV) present the heat gain estimation for building using CLTD/SCL/CLF method.This method estimates heat gain by selecting one by one component of the building.Table (X) shows the conduction gain through wall from1 pm to 6 pm.The average conduction gain through south wall is 3473.32W, conduction gain through north wall is 4002.25 W, and conduction gain through east wall is 5653.12W and through west wall is 3448.87W.
Table XI shows the conduction heat gain through roof.The total conduction heat gain through roof is 27106.51W. From comparative study of all the three methods it can be seen that CLTD/GLF method predicts heat gain towards lower side whereas CLTD/SCL/CLF method values are higher and RLF values lies in between being more close to CLTD/SCL/CLF method.An important point to notice on comparison of results is that all methods predict around 50% heat gain through roof for this building structure.Another major contribution to heat gain (around 30%) is through walls.The window to wall ratio for the building is 1.9% and therefore the effect of heat gain through windows is only around 8%.Other factors contribute only a minor percentage to the overall heat gain.Thus, from the results it can be concluded that in order to reduce the heat gain and cooling load, major attention must be paid on roof and wall heat gain along with the other factors.In this study the major heat gain occurs from wall and roof and less heat gain is through windows as window area is less.There are various passive measures including insulating layers on wall and roof, white paint on roof, cool coatings, inverted earthen pots on roof, roof pond etc. which can help to reduce heat gain through roof and wall and enhance thermal comfort of buildings [26,27].The heat gain from window can be reduced by applying low e coating on window glazing, by using overhang, curtains, awnings and also with the help of shading by trees.

VIII. CONCLUSIONS
The paper presented the study of heat gain for various components of a typical middle income group residential house in hot dry climatic region in India.For the heat gain study three different methods (CLTD/GLF, CLTD/SCL and RLF methods) were used and compared.From the study it can be concluded that methods which are used in the study are simple and can be used in manual calculation or spreadsheets.The advantage of this study is that the heat gain over various components/processes of building such as roof, walls, windows, infiltration, appliances, occupants etc. can be calculated.CLTD/GLF and CLTD/SCL methods give results of wall heat gain with orientation whereas RLF method results do not specify direction of walls and window.CLTD/GLF method uses specified values whereas CLTD/SCL method has flexibility of allowing variations.CLTD/GLF method predicts heat gain towards lower side whereas CLTD/SCL/CLF method values are higher and RLF values lies in between being more close to CLTD/SCL/CLF method.It is very useful study to get the basic knowledge about heat gains of building and it also helps in better designing of the building with less heat gain

Fig. 1 .
Fig. 1.External and internal heat gain for a building meter.One bedroom has window on south of 1 m x 1 m and other bedroom has window on east of 1 m x1 m.Both bedrooms have one attached bathroom of size 3 m x 3 m.The size of living room is 9 m x 9 m.Living room has door on north of 1m x1.5 m meter.The size of kitchen is 3 m x7 m.Kitchen has west side window of 1 m x1.m.All windows are operable.The size of storage room is 5 m x 3 m.

Fig. 2 .
Fig. 2. Dimensions and plan of the residential building taken for studyTABLE I: CONSTRUCTION TYPE OF HOUSE Component Details Roof construction

TABLE VII :
HEAT GAIN OF BATHROOM From table II to VII the sensible heat gain of different places of house are shown.The table VIII show total sensible heat gain of each place.The ventilation heat gain is determined separately.

Table
(12)hows the CLTD values for walls which are used to calculate conduction heat gain presented in table X.TableX, XI and XII shows the conduction heat gain through wall, roof and door.It is determined using(12).Here heat gain is calculated at different hours of the day from1 pm to 6 pm in July month TableXIIIshows the conduction gain and solar gain through glass.Tables XIV and XV present the internal heat gain and total internal heat gain.

TABLE XIV
Light and appliances -The light and appliances load is assumed 470 Watt.

TABLE XVI :
OPAQUE SURFACES FACTOR

TABLE XXII :
COMPARATIVE ANALYSIS Table XII shows the conduction heat gain through door and the total heat gain is 136.78W. Table XIII shows the conduction heat gain through glass and it is 347.67 W. The solar heat gain through glass is 28 W for south, 48 W for east and 100 W for west.Table XIV presents the internal heat gain due to occupant, infiltration and light, appliances.The sensible heat gain due to residents of the building is 280 W and latent heat gain for this method is 180 W. Due to infiltration the sensible heat gain is 836.4W and the latent gain is found to be 662.2W. The heat gain due to light and appliances is assumed to be 470 W. The total heat gain calculated is 46774 W. From table XVI to XX the heat gain of building estimated using RLF method is presented.Table XVI presents the heat gain through opaque surfaces and it is 24638.8W for ceiling, 15836.63Wfor wall, 89.26 W for door.Table XVII presents heat gain through fenestrations and it is 225.16W for west, 113.68 W for south, 225.16 W for east.Table XVIII presents the heat gain due infiltration or ventilation and sensible heat gain due to infiltration is 1268.82W and latent gain is 1004.56W. Table XIX shows the internal heat gain including sensible and latent gain.Sensible load is 598 W and latent gain is 95.6 W. Table XX presents the total sensible and latent heat gain with the total gain as 44096 W.