Building loads evaluation

Space loads (sensible and latent)

= [Q roof + Q walls + Q windows + Q people + Q lights + Q appliances]

Building Loads

ASHRAE Standard 55 does NOT cover this condition for human comfort

Thermal mass

Ability to temporarily store heat (cp: specific heat) • Time component • Transient effect; non-steady state • Impacts interior loads • Significant impact on calculating cooling loads • High mass buildings vs. low mass buildings

False

As we discussed this week minimum outdoor temperatures in winter commonly occur shortly before sunrise. As a result ASHRAE recommends that radiant solar and internal heat gains such as lighting and plug loads should not be considered when calculating heating loads

False

Changes in Latent heat will result in a measurable change in DB Temp

Q = U * A * ∆T

Conduction through completely shaded walls, roofs interior partition walls, (suspended) ceiling, floors and for heating load calculations

Q = U * A * CLTD

Conduction through sunlit surfaces all exterior walls, roofs, windows and skylights CF adjusts for actual indoor/outdoor design and daily range

CLTD method

Cooling Load Temperature Differential

CLTD

Cooling Load Temperature Differential • Thermal mass, other effects accounted for through CLTD Sunlit material surfaces (direct and reflected) • Conduction Walls, roofs, windows (+ radiant solar) • Tabular data • CLTD Correction Factor (CF) (78°- inside design temp) + (design outdoor temp - 85 - (daily range/2))

Partition, roof, floor, wall, glass solar, glass conduction

External load components

Q = U * A * ∆T

Generalized heat transfer equation U = overall heat transfer coefficient [Btu/hr-ft2 -ºF]

Ventilation (outdoor "fresh" air)

Generally a coil load, not a space load

25 people

If the space measures 500 ft.² and the design occupancy is 20 ft.² per person, how many people are in the space?

It accounts for the capacity of the space to absorb and temporarily store heat It determines the radiant component of the plug load It describes a space ability to resist heat flow It accounts for the latent component of the plug load

In the equation for calculating plug loads, Q = watts x 3.41 x %use x CLF What purpose does the cooling load factor CLF serve

QS = 1.085 * CFM * ∆T QL = 0.68 * CFM * ∆gr

Infiltration (sensible and latent) air change, crack length, leakage area methods ∆T from design conditions, ∆gr from psych chart

Partition, misc, people, infiltration, ventilation, lights, plenum

Internal & other load components

Q = watts * 3.41 * ballast factor * CL

Lighting (sensible only) ballast factor always increases lighting load

conduction, convection, radiation

Methods of heat transfer

Block vs. Sum of Peaks

Peak Load, in an area, refers to the greatest design load at some time of day for that area. Block load refers to the highest combined loads of areas being served by the heating or cooling equipment

QS = # people * sensible gain/person * CLF QL = # people * latent gain/person

People (sensible and latent) CLF similar to CLTD and SCL: thermal mass of space

Q = watts * 3.41 * %Use * CLF

Plug loads: equipment / appliances (sensible and latent) office equipment, coffee makers NOTE: commonly, CLF = 1.0 (space temp reset)

Conduction calculation example (heating)

Q = U * A * ∆T (STEADY-STATE CONDITIONS) by convention: Q will be NEGATIVE when losing heat

Infiltration

Qinfil(S) = 1.085 * CFM * ∆T Qinfil(L)= 0.68 * CFM * ∆gr

Lighting• Sensible and/or latent • CLF or usage factor

Qlights = watts * 3.41 * ballast factor * CLF

Solar Radiation

Qsolar = A * SC * SCL

U Value

Quantifies the flow of heat Btu/hr∙ft2∙ºF U = 1 / R

Ventilation (outdoor "fresh" air)

Qvent(S) = 1.085 * CFM * ∆T Qvent(L)= 0.68 * CFM * ∆gr

Q = A * SC * SCL

Radiation through windows

Qsolar = A * SC * SCL

SC is based on: Number of panes,Color, Reflectiveness, Film

Qsolar = A * SC * SCL

SCL is based on: Direction Time of Day Day of the Year Latitude Internal shading devices Interior finish Thermal mass

Air change method Building pressurization method Crack method

Select the three common methods for calculating infiltration

People

Sensible and latent • Activity tables • CLF assumption • NOTE: CLF = 1.0 if load is present 24/7, or if space temp is 'setback' at night. Qpeople(S) = # of people * sensible heat gain/person * CLF Qpeople(L) = # of people * latent heat gain/person (NO clf)

Lighting

Sensible • Ballast factor (except incandescent) • CLF assumption • Percent to space

Solar radiation

Shading Coefficient (SC) • Solar Cooling Load Factor (SCL) in some references, a.k.a. 'Solar Factor' (SF

Temporarily store heat

Thermal mass characterizes a material 's ability to

Infiltration

Variable • Airflow estimation methods Air change method CFM = (volume of space * air change rate) ÷ 60 Crack method Tabular data based on linear feet of crack - Effective leakage-area Detailed calculation - wind speed, shielding, and stack effect

QS = 1.085 * CFM * ∆T QL = 0.68 * CFM * ∆gr

Ventilation (sensible and latent) - same equations as infiltration - coil load only!

R-value Is inversely proportional to the U factor

What is the relationship between R-value and U-factor

Radiation

Which of the following basic heat transfer methods is best described as a process heat by means of electromagnetic waves including infrared and visible light?

Q= U x A x CLTD

Which of the following formulas would one use to calculate the conduction through sunlight glass

Q= U x A x CLTD

Which of the following formulas would you use to calculate the condition load of a completely shaded wall

Q= U x A x CLTD

Which of the following formulas would you use to calculate the condition load of the sunlit wall

Q = A x SC x SCL

Which of the following formulas would you use to calculate the radiation through glass

R-value

Which of the following values accounts for thermal mass of a roof or wall?

return air People Receptacle Infiltration

Which of the following would not be considered a space load

True- Infiltration is typically considered during the space load X -calculation X -The crack method is one way to calculate ventilation air X- Ventilation is a Latent only space load X- Infiltration describes outdoor air intentionally brought into the building

Which one of the following statements about ventilation in infiltration is true

True

as discussed this week, min outdoor temps in winter commonly occur shortly before sunrise. As a result, ASHRAE recommends that radiant solar and internal heat gains (lighting, plug loads) should NOT be considered when calc heat loads

Design weather is "worst case" data; analysis weather reflects typical conditions

difference between design weather and analysis weather

Miscellaneous (receptacle or "plug") loads

• Sensible and/or latent • CLF or usage factor Qmisc= watts * 3.41 * CLF Qmisc= sensible * usage factor Qmisc= latent * usage factor

Q = U * A * CLTD WALL

• Temperature Difference • Direction • Time of Day • Day of the Year • Latitude • Surface Color • Daily Range • Wall Type (-thermal mas) WALL CONDUCTION