Question

1. (8pts) Heating load represents the amount of heat that needs to provide to a room to maintain a designed indoor temperature. The main heat loss is the heat transfer via building envelope (exterior walls and roof) and windows. Assume you are required to design a heating system for a building, and the first task is to compute the building loads. In your analysis, would you prefer to treat this as a transient or steady-state heat transfer problem? Also, would you consider the heat transfer via building envelopment to be one-dimensional or multidimensional? Explain. (Please make sure your handwritings are neat and readable!!)

Answer 1

Design a heating System ford building * Choose the System 0 insulation, access 1 Look at the building podometers for size type and Construction like:- Area, number of prooss, Type of foof, meigbosing stouetunne , function of the buifaing, envelope, to roof etc - Cher focal climare (bpoke temperature Fiumicity , latitude ete) System installers and system manufactur- ers usually recommend 20% to 50% more ñeat than you can make do with If you want more than 20°C in aer rooms in mid-wintes take their advice. Otherwise wear more clothing and accepe 17°C or more in all living area cond la'c or more in med bedroo řns, during cold Apells in Winter. * In most location, g would recommend mig conditioner in each one reverse cycle room or connected pair of rooms, not one centraf unit. This gives better independent control of spaces to save operating Core.

e For heating systems, the critesia -include Efficiency & heat to home interior/ (he heat to home interior of heat rost up the flue Adequote Vertical mixing of the oid in the home A de quale size for Worst Case heating dond of the year - one very cold night mokes a lasting impoe msion on the owner. Willingness to get as much information before the proctose decision Noise level - Eng furnace blower or radiant heating pump • Installed Cost Cost operating (fuel) As needed Cioculating Maintenance Coat compute the building lood & Heat load Calculation for any type of building, following steps should be taken it

Calculate the heat generated by occupanta Stepone: Calculate the area in square feet of the space to be cooled ond multiply by 31.25 Area BTU = length (ft) x wid rf (ft) X 31.25 Loss by 1.4 facing - Step Two Calculate the heat got the ough the Windows of the Windows don't have Shaling multiply the result North Window BTU = Area of North Windows (m.sq) x169 If no shading, North Window BTU - Nouth Windows BT UN119 South Windows BTU: Area of South facing Windows (m.sq) * 868 of no shading, South Windows BTU - South Windows BTU X 114 Add the Result togerner Total Windows BTU = North Window + South Window Step Three . ollow 600 BTU per person occupont BTU = Number of people X 600

each of X 3.4 lighting Step Four Calcupole the heat machinery - Copier, computers, ovens etc. generated Find thie power in wettig for each item, add them together and mustippy by 3.4 Equipment BTU: Totale quipment Watts Step Five Colculate the heat generated by lighting Find the total Wattage for ARP and multiply by 4.25 Lighting BTU = Total lighting Worty X 4.25 Step Six Add the above together to find the total heat lood Total heat lood BTUE Area BTUI Total Window BTU F occupant BTU f Equipment BTU & Lighting BTU Step Seven * Divide the heat dood Cooling Cosperity of the mid Conditioning unit in BTU DO determine how many nio conditioned ore needed # Alumber of alcunit required . To top he or lond BTU) Cooling Capacity BTU

but conseovative approach that leads to slight overestimation of the heating (opacity. outdoor conditions donat As the name implies, heating load Calculation are carried out to estimate the heat loss from the building in Winter so as to oroive at required heating Capacities. Noomarly during winter months, the peok fie ating dond occors before sunrise and the Very significantly the Eightut the winter season In addition, internal he of sources such as occupanty od appliances ore beneficial as they compenaate some of the heat losses. AS A Result, normally the foot lood calculation are carried out nauming steady state conditions (no solar radiaton cond steady out door conditions)ond neglecting internal fie at source. This is simpio ► has to take into For more accurate estimation of lood, one account the thermal Capacity of the heating

O Walls and internal heat source, which mokes the problem more complicated Heat transfer Majority of treat transfer takes place in building through building envelope. Building envelope consist of works, roof and fenestrations (opening) Hent Conduction transfer through Wolls and roof is by Conduction and is through conduction cond rooliation in grazing materials o rent loods are generated through convection which is teamed as Ventilation lond. These are also internal load inside the building due to occupancy. Heat transfer throu ugh * Heat toonster through a material toky place by conduction from Worm to cold side. The same process 2M takes place in a bu Generally, the thermal Conductivity of the building materials will be much lower. In sotid bodies including building componente, theomar Conquetion to key proces wines one poor of the component is subjeften bu ilerling

to highes temperature and the other port to a lower temperature Condition most cases of theam of Conduction are usually analysed and treated in their simplified foom ng one dimension of the at flow coses ie heat flow in direction other otron the main direction is negrected. * Similary if the change in atmospheric Condition (inside) outside) ore susumed to be Very slow, neglecting these changes, the proces of heot toons for con be inssumed to bed! Steady stare heay tronafern Heat tòansfer through convection when heat is transported by fluid like mit od water, this is called Convection. The extent of Convective he ot troverer depends on number of things like the position of the surface, but mainly on the speed of the possing oir.

tronefer is Sensible heat is defined as the heat • Heat transfer through Radiation the phenomenon of therm op rodiotron is described as the tromsport of energy through electromagnetic Woves i uneike Conduction and Convection, roaration Reat no bound with material, it Con even occur through voccam. hie et transfer through rmelinton these energy the role of heat flow depends on the temperature of the emitting and deceiving surface and certain qualities of surface. Radiation received by a surface con poorly be absorbery and poorty eng be reflected. Heat is toonsferred into the building through rnaraton from the grain poovided for fenestrations Copening) Sensible heat heat 0 stored in a substanco As a result on increase in its temperature Latent & Lotent heat is defined as the heat flour to or from a motenor without a change to temperature. The heat will only change the structure or phase of the material,