Heating and Air Conditioning I Principles of Heating, Ventilating and Air Conditioning R.H. Howell,...

Heating and Air Conditioning IPrinciples of Heating, Ventilating and Air

ConditioningR.H. Howell, H.J. Sauer, and W.J. Coad

ASHRAE, 2005

basic textbook/reference material

For ME 421

John P. Renie

Adjunct Professor – Spring 2009

Chapter 6 – Residential Cooling/Heating• This chapter covers the calculations for design cooling and heating

loads for residential buildings.• Calculate of the heat loss and heat gain to estimate the capacity of the

heating and cooling components to maintain comfort.• Based on extremes – peak loads conditions – Chapter 29 of ASHRAE

Fundamentals• Residences and small commercial buildings – dominated by the external

envelope (walls, roof, windows, and doors)• Large commercial building often dominated by internal gains (occupants,

lights, equipment, and appliances)• All buildings need to consider energy required to heat/cool and humidify/de-

humidify due to infiltration (either intentional or leakage)• Methods for commercial not applicable to residential – temperature swings• Same methods as non-residential (Chapter 7) – with care

Chapter 6 – Residential Cooling/Heating• This chapter covers the calculations for design cooling and heating

loads for residential buildings.• Residential buildings distinquished by:

• Smaller internal gains – dominated by structural gains/losses and infiltration• Varied Use of Spaces – localized conditions tolerated• Fewer Zones – usually single zone – single thermostat – swings – moderating

the peak load due to heat storage within building• Greater Distribution Losses - duct losses/gains significant• Partial Loads – systems are small (1 to 5 tons) – at capacity only rarely

leading to running at partial capacity – oversized detrimental to good seasonal performance

• Dehumidification Issues – only during cooling season – thermostat controlled by sensible heating – short-cycling – degraded dehumidification

• Categories• Single family detached – four walls, single thermostat, open – centralized air return

• Multi-family – less exposure – not same load leveling

• Other – dependent on east-west fenestration

Chapter 6 – Residential Cooling/Heating• Residential characteristics can lead to complex load calculations

• Hour-by-hour methodology required to find peak• Different methods for heating and cooling due to simplification for heating• Heating uses worst case – no solar or internal gains and no storage – reduces

to UAt calculations• Cooling methods revised due to computation speed availability – 24 hour,

equation-based procedures• Cooling method based on Residential Load Factor (RLF) methodology – a

simplified procedure derived from a detailed residential heat balance (RHB) analysis of buildings across the range of climates – applicable to spreadsheet

• RLF Limitations given in Table 6-1• Latitude – 20 to 60 degrees North

• Date – summer peaking (July 21)

• Elevation – below 6,500 ft

• Climate – Warm/hot

• Construction – Lightweight residential

• Fenestration area/tilt – 0 to 30% total floor area

• Occupancy - residential

• Temperature swings and Distribution losses

Chapter 6 – Residential Cooling/Heating• RLF Limitations (Table 6-1)

Chapter 6 – Residential Cooling/Heating• General Guidelines.

• Following guidelines apply for both heating and cooling.• Design for typical building use – meet maximum load conditions – not

extreme conditions (parties, etc.)• Building code and standards – local codes take precedence• Designer judgment – prior projects, local building practices• Verification – post construction – pressure testing• Uncertainty and safety allowances – safety allowances should be

added at the end to avoid compounding effect.


• Basic relationships


• Design Conditions• Indoor conditions

• Cooling 75 oF db and 50 – 65% RH

• Heating 68 – 72 oF db and 30% RH

• Outdoor conditions• Cooling – 1% values in Table 4-7

• Wind speed 7.5 mph

• Mid-summer – or early fall for south-facing building

• Heating – 99% values in Table 4-7

• Ignore solar and internal gains

• Several-day extreme events

• Wind determinant for infiltration

• Possibly use 99.6% value as extreme or 99% with safety factor

• Adjacent buffer spaces

• Uninsulated garages and attic – at outdoor temperature

• Insulated, unheated spaces at average temperature


• Building Data – Component area• Gross area – outside building area discussion• Fenestration area – entire product area (framing)• Net area – gross minus fenestration• Volume – Floor area x floor-to-floor height

• Building Data – Construction Characteristics• U-factors – use Chapter 25 or manufacturer’s data (under heating

conditions)• Fenestration

• U-factors and solar heat gain coefficient (SHGC) for entire assembly

• Table 6-2

• Only and few different types of glazing

• Storm window treatment

• Interior and exterior shading included during cooling loads


• Building Data – Table 6-2


• Load Components• Below grade surfaces – zero for cooling – non-zero for heating• Infiltration – significant portion of heating and cooling loads (see

Chapter 5) – evaluated for entire building• Leakage rate (Q or ACH)

• Caused by building effective leakage area

• Driving pressure caused by bouyancy and wind


• Caused by building effective leakage area

• Leakage area – measure AL by a pressurization test, or


• Unit leakage area (Table 6-3)


• Evaluation of Exposed Surface Area (Table 6-4)


• Infiltration Driving Force (IDF) in cfm/in2


• Infiltration Driving Force (IDF) in cfm/in2 – H = V/Acf


• Load Components• Ventilation – whole building ventilation – need to be included

• Distribution Losses• Can cause substantial equipment loads in excess of building requirements

• Dependent on location of duct runs, length, surface areas, surrounding temperature, duct wall insulation, air-tightness

Chapter 6 – Residential Cooling/Heating• Cooling Load Methodology.

• Determines the total sensible cooling load from heat gain1. Through opaque surfaces (wall, floors, ceilings, doors)

2. Through transparent fenestrations

3. Caused by infiltration and ventilation

4. Cause by occupancy.

• Peak Load Computation – sum of all rooms

• Opaque Surfaces – t and solar gains incident


• Opaque Surfaces – t and solar gains incident• OF factors represent construction-specific physical characteristics• If OF less 1 (buffering affect of attics and crawlspaces)

• OFb incident solar gain

• OFr captures heat storage effects by reducing the effective temperature difference

• Old technique – CF = U x CLTD


• Opaque Surfaces – t and solar gains incident• Roof Solar Absorptance


• Slab Floors – slight reduction in cooling load – or ignored


• Transparent Fenestration Surfaces - nondoor


• Peak exterior irradiance – with shading

Chapter 6 – Residential Cooling/Heating• Cooling Load Methodology – primary exposures

Chapter 6 – Residential Cooling/Heating• Cooling Load Methodology – for any exposures.

Chapter 6 – Residential Cooling/Heating• Cooling Load Methodology – transmission of exterior

attachments.


• Shaded fraction – 1 if adjacent building or …

Chapter 6 – Residential Cooling/Heating• Cooling Load Methodology

• Shade line factors.


• Solar load factors, FFs

• Value of FFs corresponds to fraction of transmitted solar gain that contributes to peak cooling load.


• Solar load factors, FFs


• Interior attenuation coefficient, IAC


• Internal Gains – effect of occupants, lighting, and appliances


• Total Latent Load• Caused by three predominant moisture sources, outdoor air

(infiltration and ventilation), occupants, and miscellaneous sources (bathing, cooking, etc.)

• Summary of RLF Cooling Load Equations (Table 6-14) … see next slide


• Summary of RLF Cooling Load Equations (Table 6-14)

Heating and Air Conditioning I Principles of Heating, Ventilating and Air Conditioning R.H. Howell,...

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