Mech/Elec ALS Lesson One - Basic Thermal Processes: Heat Load Calculations - Conduction

Building Heating load = Sum of all losses through the building skin

Conduction Formulae

Same formula for roofs, walls, windows or doors

Any given instan / instantaneous version

Determines the case at a particular moment, usually called design day, this day is colder than 98% of the other days, if equipment can handle the load for that day then other days will be taken care of.

Heat flow = product of conductance of the assembly / the U value X Temperature difference between inside and outside X exposed surface Area

Qc = U(A)(T_inside - T_outside)

Any given day / degree day version

Used to compare two alternatives over a lobger period of time.

able to analyze a payback period on investment, i.e., how many years of reduced energy costs it would take to pay for the increase in insulation

Qc = U(A)24(DD)

DD = degree days

Qc = Btu's

One degree day = any given day where temp. is one degree below 65deg

Two degree day = any given day where temp. is two degrees below 65deg

65deg's is the mean reference

For heat loss, days over that temp are disregarded.

This last equation gives the ability to calculate the degree days for a particular locality over a period of time, even an entire winter for heat loss.

Mild winter = 3,000 degree day winter

Severe winter = 7,000 degree day winter

INstantaneous version fo Qc is used to determine the case at a particular moment, ussually called the design day.

Design day = a day colder than 98% of the days experienced in a given climate. If the heating equipment and plant are sized to keep the building warm on that day, they would be sufficent for the other 98% of thedays also.

Degree day version of the formula for Qc may be used to compare two alternatives over a period of time. Possible to determine a payback period on an investment.

Study time: 5/24 9:15-9:45pm 0.5 hours