designing for heating and cooling

8 Chapter 8: Designing for Heating and Cooling

Chapter in Brief

This extensive chapter addresses the preliminary development of heating and cooling system options during schematic design and the further refinement of selected options during design development. In effect, the chapter covers how the problem of heating, cooling, and lighting a building should be organized in the early design stages, provides extensive data resources and examples to structure the preliminary systems analysis process, and more extensive data and examples to move systems analysis into design development. The schematic design of daylighting is included because early design decisions regarding daylighting have such a dramatic impact on heating and cooling loads and approaches. More detailed information regarding HVAC systems and lighting design is provide in subsequent chapters.

Establishing an appropriate design intent for the building type and climate is a crucial first step in climate control system design. Bioclimatic charts and a sense of whether a building will be internal-load dominated or skin-load dominated can help get the process on the right track. Building form, orientation, zoning, opaque envelope elements, and fenestration must all be considered when making decisions regarding appropriate heating, cooling, and daylighting strategies. These three systems will interact and there will almost always be a need for trade-offs between systems. Zoning is especially important as a means of grouping like spaces for thermal and lighting purposes. Understanding space function, schedule, and orientation is the key to successful zoning.

Daylighting design guidelines are given for schematic design. Preliminary daylighting design involves establishing daylighting design intents, daylight factor (DF) criteria for the various building spaces, estimating daylighting system performance, and comparing estimated performance to criteria. Tables and figures to assist in these tasks are provided, along with worked examples of the procedures. Window height and area are key factors in sidelighting approaches. Distribution of daylight should be qualitatively considered; lightshelves and combination toplight/sidelight approaches can improve distribution.

Passive solar heating is presented as a viable design strategy for many building types and climates. The philosophy of “insulate before you insolate” is emphasized. Building heat-loss (winter) design criteria are provided for solar and non-solar buildings. Solar savings fraction is introduced as a measure of passive solar heating system performance. Design criteria for performance of a generic passive solar heating system include “standard” and “superior performance” options. Thermal mass (masonry, water, rock beds, and phase-change materials), mass distribution, and orientation of solar glazing are discussed as design elements. Criteria for roof ponds are also presented. Guidelines for collector area and tilt and thermal storage are also given for active solar heating systems. Data tables and figures and worked examples are provided.

Guidelines or criteria for heat gain (summer) are given, a distinction being made between intentionally “open” (such as naturally ventilated) and “closed” building design approaches.

CHAPTER 8: Designing for Heating and Cooling

These heat gain criteria are followed by guidelines for preliminary design of a range of passive cooling systems including cross ventilation, stack ventilation, night ventilation of thermal mass, evaporative cooling, cool tower, roof pond, and earth tube approaches. Extensive data tables and figures and worked examples are provided.

Following the presentation of design criteria and preliminary analysis methods, the chapter considers the need to re-integrate building needs and potential daylighting, heating, and cooling solutions. The possibility of conflict between design intent and prescriptive code requirements is mentioned. Tradeoffs between systems are further discussed.

Calculations for design heat loss and design heat gain are explained and illustrated, along with the assumptions underlying these procedures. The use of these calculations to explore opportunities for design improvements and to compare estimated building performance against established benchmarks is emphasized. Calculations for estimating heating season fuel consumption are presented. The concepts of balance point temperature, degree days, system efficiency, time lag, and temperature swing are introduced. Sensible and latent heat effects are differentiated. Psychrometrics, the psychrometric chart, and psychrometric processes are explained.

The chapter concludes by revisiting all the passive heating and cooling systems previously considered at the schematic design level by expanding upon the specificity and detail of analysis methods. “As building design takes shape, more-detailed information becomes useful.” For heating systems, this level of consideration addresses glazing, direct gain systems, sunspaces, trombe walls and water walls, and combination passive heating systems. The load-to-collector (LCR) analysis procedure for annual system performance is explained. The sensitivity of systems to design variations is considered. For cooling systems, design development procedures for cross ventilation, stack ventilation, night ventilation of thermal mass, fan-assisted evaporative cooling, cooltowers, roof ponds, and earth tubes are presented. Detailed data tables and examples are provided throughout.

Chapter Outline

8.1 Organizing the Problem(a) Fenestration(b) Building form(c) Building envelope

8.2 Zoning8.3 Daylighting Considerations8.4 Passive Solar Heating Guidelines

(a) Whole-building heat loss criteria(b) Solar savings fraction (SSF)(c) Thermal mass(d) Orientation(e) Roof ponds(f) Active solar heating

8.5 Summer Heat Gain Guidelines8.6 Passive Cooling Guidelines

(a) Cross-ventilation(b) Stack ventilation(c) Night ventilation of thermal mass


(d) Evaporative cooling(e) Cooltowers(f) Roof ponds(g) Earth tubes

8.7 Reintegrating Daylighting, Passive Solar Heating, and Cooling8.8 Calculating Worst-Hourly Heat Loss

(a) Maximum hourly loss: sizing conventional heating equipment(b) Maximum hourly loss: sizing auxiliary heating for passive solar buildings(c) Maximum hourly loss: checking design criteria(d) Hourly rates of fuel consumption

8.9 Calculations for Heating-Season Fuel Consumption (Conventional Buildings)(a) Balance point temperature(b) Degree days (DD)(c) Yearly space heating energy

8.10 Passive Solar Heating Performance(a) Glazing performance(b) Direct-gain (DG) systems(c) Sunspaces (SS)(d) Trombe walls (TW)(e) Water walls (WW)(f) Load collector ratio (LCR) annual performance(g) Variations on reference systems(h) Thermal lag through mass walls(i) Internal temperatures

8.11 Approximate Method for Calculating Heat Gain (Cooling Load)(a) Gains through roof and walls(b) Gains through glass(c) Gains from outdoor air(d) Gains from people(e) Gains from lights(f) Gains from equipment(g) Latent heat gains

8.12 Psychrometry(a) Cooling process(b) Heating process

8.13 Detailed Hourly Heat Gain (Cooling Load) Calculations8.14 Passive Cooling Calculation Procedures

(a) Cross-ventilation(b) Stack ventilation(c) Night ventilation of thermal mass(d) Fan-assisted evaporative cooling(e) Cooltowers(f) Roof pond cooling(g) Earth tubes(h) Passive cooling summary

8.15 Case Study: Designing for Heating and Cooling (Blue Ridge Parkway Destination Center)References

Key Concepts


General: organizing the design problem (as a starting point for thermal design) codes and standards (as setting minimum performance or component requirements) key design issues for heating, cooling, daylighting (as they direct design efforts) design criterion as a function of building type (conventional or passive) zoning (as a design organizer) daylighting (as it influences heating and cooling loads) internal-load dominated (as a result of building form, function) skin-load dominated (as a result of building form, function) balance point (and balance point temperature; as a design tool) design conditions (as input to calculations) tradeoffs (likely a necessary part of design process) efficiency (as a system metric and objective) system sensitivity (as a design tool) thermal lag (a physical phenomenon and design strategy) temperature swing (interior air temperature; as a performance indicator) sensible heat (involving temperature change) latent heat (involving moisture) psychrometrics (psychrometric chart and processes; as design tools)

Daylighting: daylighting approaches (sidelighting, toplighting; as organizing principles) daylight factor (as a design criterion)

Solar Heating: “insulate before you insolate” (as a recommendation) passive solar heating (direct gain, sunspace, trombe wall, water wall, roof pond) effects of solar heating on purchased and total energy quantities (to be understood) solar savings fraction (SSF, as a measure of solar performance) load collector ratio (LCR, as a relative indicator of system size) building load coefficient (BLC; a performance metric) thermal mass (masonry, water, rock bed, or phase-change materials; as a system

component) orientation (as a determinant of building layout and window/collector location) active solar heating (as a mechanical system solution)

Passive Cooling: passive cooling (ventilation—cross, stack, and of thermal mass, evaporative cooling,

cooltower, earth tube, roof pond ) transparent insulation materials (TIM; an emerging technology) coolth (as the conceptual opposite of heat)

Important Terminology

internal-load dominated skin-load dominated zone daylighting

toplightingsidelighting


daylight factor (DF)clerestorylightshelf

solar savings fraction (SSF) eutectic salt rock bed tilt azimuth cross ventilation stack ventilation design data

mean daily range (MDR, of temperatures)design dry-bulb temperaturemean coincident wet-bulb temperatureheating degree daycooling degree daycooling degree hour

efficiency annual fuel utilization efficiency load collector ratio (LCR) building load coefficient (BLC) sensitivity curves ∆t solar (delta t solar) sensible heat latent heat sol-air temperature design equivalent temperature difference design cooling load factor infiltration factor ventilation factor psychrometric chart

dry-bulb temperaturewet-bulb temperaturerelative humiditydew pointsaturation linehumidity ratiodensityspecific volumeenthalpy

Important Metrics

DF (daylight factor) cfm (air flow rate, cubic feet per minute) HDD (heating degree day) CDD (cooling degree day; and hour—CDH)

Look For


Table 8.1, which maps out the contents of Chapter 8 (a useful navigation tool).

The case study of the Blue Ridge Parkway Destination Center.

Figures 8.1 and 8.2 illustrating the relationships between daylighting, heating, and cooling in internal- and external-load dominated buildings, respectively.

Example 8.1 (with multiple parts distributed throughout the chapter), which details preliminary and then more detailed design calculations and system sizing for a sample building and a variety of heating, cooling, and daylighting strategies.


The numerous sizing and analysis tools (often in the form of figures and tables) for passive heating and cooling systems design that are presented in this chapter. A matrix that organizes these resources by stage in the design process follows [page numbers are noted in brackets]. Substantial additional information on elements such as glazing orientation, phase-change thermal storage and rock bed sizing, interior air temperature swings, and the like is presented in the text of the chapter—but not referenced in the table below. See Example 8.8 [page 257] for a systems integration walk-through.

System Aspect Target/Criterion Values

Rough Estimation of Performance

Refined Estimation of Performance

Building heat loss

Table 8.3 [230] Calculations (see Example 8.1, Part B [231])

Detailed calculations

Building heat gain

Table F.3 [1648]

Calculations (see Example 8.1, Part D [240])

Detailed calculations (see Tables F.5-F.10 [starting on 1651])

Daylighting Table 14.2 [601] Table 14.4 [603] (see Example 8.1, Part A) [223]

Chapter 14

Passive solar systems

Table F.1 [1644]; Fig. 8.8 [232]; select reasonable target for generic system

South glass to floor area ratio and Table F.1 [1644] (see Example 8.1, Part C [234])

See information for specific system types below

Thermal mass Table F.2 [1647] (see Example 8.2 [235])

Direct gain use generic target Appendix H (see Example 8.1, Part H [273])

Appendix H (see Example 8.1, Part H [273])

Trombe wall use generic target Appendix H Appendix H

Water wall use generic target Appendix H Appendix H

Sunspace use generic target Appendix H Appendix H

Active solar heating

Table F.1 [1644] (using SMALLER of the window/floor area ratios)

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Passive cooling Design judgment based upon climate and building type




Cross ventilation

Judgment Fig. 8.13 [241] (see Example 8.1, Part E [241])

Calculations (see text)

Stack ventilation

Judgment Fig. 8.14 [242] Calculations (see text)

Night ventilation ofthermal mass

Judgment Fig. 8.16 [245] (see Examples 8.3 [244] & 8.1, Part F [246])

Calculations (see Table 8.14 [297] & Example 8.1, Part J [299])

Evaporative cooling

Judgment Fig. 8.18 [250] (see Example 8.4 [247])

Calculations (see Example 8.14 [304])

Cooltowers Judgment Fig. 8.20 [251] (see Example 8.5 [248])

Calculations (see Table 8.17 [307])

Roof ponds Judgment Pond area = floor area; depth of pond = 3-6 in. (see Example 8.6, Part A [253])

Calculations (see Example 8.6, Part B [309])

Earth tubes Judgment Fig. 8.23 [256] (see Example 8.7, Part A [256])

Calculations (see Example 8.7, Part B [314])

Discussion Questions

1. It is critical to building performance that the design process make the right first steps—backtracking in practice is often too difficult and time-consuming. Outline the steps you would take during schematic design and design development to ensure that passive heating/cooling and daylighting potentials are properly evaluated and appropriate system responses included in your design process.

2. Tradeoffs are an integral part of the design process. Discuss some of the “internal” tradeoffs that may be necessary when designing passive heating/cooling and daylighting systems. Discuss some “external” tradeoffs you would expect to find between design of these climate control systems and other building systems (for example, functional relationships, circulation, security, aesthetics).

3. The book notes that highly-solar buildings may consume more total heating energy, but less purchased heating energy, than a comparable conventional building. Why? What are the implications of this situation to sustainability and to the owner?

4. Describe the difference between design guidelines or criteria and design performance. Explain the relationship between the use of guideline/criteria tools and performance tools during the design process.

5. In your opinion, at what point in the design process should responsibility for design of passive


heating, passive cooling, and daylighting systems generally be transferred from the architect to an appropriate consultant? Does the transfer point differ between these three systems? If so, why?

Exam/Quiz Questions

1. A tall building has deep floorplates and is illuminated primarily by electric light sources. This building is most likely to be:

(a) an envelope-dominated building(b) a switch-dominated building(c) an internal-load-dominated building(d) an external-load-dominated building

2. The following is NOT a factor when zoning a building for optimal thermal and lighting performance:

(a) function(b) schedule of use(c) room dimensions(d) orientation

3. Daylight factor (DF) is best defined as:(a) the ratio of daylight intensity between the brightest and dimmest points in a

building(b) the ratio of daylight intensity between summer and winter design conditions(c) the average daylight intensity at a specified point between 10 am and 4 pm(d) the ratio of daylight intensity between an interior point and an exterior reference

point

4. Which (one or more) of the following ratios are actually reasonably important to appropriate performance of the noted system:

(a) cross ventilation: the ratio of inlet opening area to outlet opening area(b) direct gain solar heating: the ratio of building heat loss to area of solar collector(b) daylighting: the ratio of window area to orientation (expressed in degrees from

North)(d) conventional cooling: the ratio of sensible heat gain to latent heat gain

5. Solar savings fraction (SSF) is best defined as:(a) the estimated savings in fuel costs of a passive versus conventional heating system(b) the annual purchased energy saved by a passive heating system compared to a

building heated by a conventional heating system(c) the percentage of annual heating load that is provided by a passive heating system(d) the incremental reduction in construction cost attributed to use of a passive

heating system instead of a conventional heating system

6. The primary difference between sensible and latent heat is:(a) sensible heat affects dry-bulb temperature, while latent heat affects moisture

content(b) sensible heat occurs in winter and latent heat occurs in summer(c) sensible heat can be handled by building systems, while latent heat can not(d) sensible heat will flow within a building, while latent heat is stationary


7. A “phase-change” material would normally be used to:(a) filter air in a conventional cooling system(b) provide transparent insulation for a passive heating system(c) ensure evaporative cooling in a cooltower system(d) store heat in a passive cooling or heating system

8. A Trombe wall is an example of which of the following passive solar heating system types:(a) sunspace(b) indirect gain (c) direct gain(d) diffuse gain

9. Draw four simple schematic diagrams that illustrate the following passive heating system concepts:

(a) direct gain(b) water wall(c) sunspace(d) Trombe wall

10. Thermal mass is a critical aspect of passive solar heating systems because:(a) the mass provides shear resistance to counteract the substantial glazing in a

passive building(b) the mass provides heat storage that tempers potentially large fluctuations in

space temperature(c) all US building codes require thermal mass in passive solar buildings(d) the mass provides insulation that ensures that collected solar heat stays in a

building

11. List three sources of internal heat gain.

12. Draw four simple schematic diagrams that illustrate the following passive cooling system concepts:

(a) stack ventilation(b) roof pond(c) earth tube(d) cooltower

13. Which of the following pairs of parameters are used as the primary (horizontal and vertical) axes on the psychrometric chart:

(a) dry-bulb temperature and humidity ratio(b) dry-bulb temperature and enthalpy(c) density and specific volume(d) wet-bulb temperature and dew-point temperature

14. Balance point temperature is best described as:(a) the indoor air temperature at which a backup heating system will take over

for a passive system(b) the outdoor temperature at which a building needs neither heating nor cooling(c) the design temperature that is used to size a conventional heating system(d) the average soil temperature at which a cool tube becomes a viable cooling option


15. What are heating degree days?(a) the average number of days that heating is required in order to maintain thermal

comfort within a building(b) the number of days in a year that the mean outside temperature is less than 65F(c) a direct measurement for a building’s energy consumption for spatial heating(d) the sum (for an entire year) of the differences between the base temperature and

the average daily temperature

16. In the context of climate control systems design, a “tradeoff” is best described as:(a) accepting less-than-ideal performance in one system to improve performance

in another system(b) seeking an exemption from building code requirements in order to use

passive systems(c) upgrading system performance (for example, from standard to superior)(d) switching from one design approach to another in order to reduce costs

17. Sensitivity curves can be used to:(a) explore the impact of changes in some parameter (such as mass thickness) on

system performance(b) determine whether a particular system is a viable design option or not(c) estimate the annual fuel consumption of a heating or cooling system(d) predict occupant satisfaction with conditions provided by heating/cooling systems

Internet Resources

Blue Ridge Parkway Destination Centerhttp://www.blueridgeheritage.com/aboutus/parkwaydestinationcenter.html

U.S. Department of Energy, Building Energy Software Tools:http://www.eere.energy.gov/buildings/tools_directory/

Vital Signs Curriculum Project Resource Module on Building Balance Point (scroll and click):http://arch.ced.berkeley.edu/vitalsigns/res/rps.html

http://www.blueridgeheritage.com/aboutus/parkwaydestinationcenter.html

designing for heating and cooling

Documents

maximum hourly loss

simple schematic diagrams

solar savings fraction

specific system types

balance point temperature

assisted evaporative cooling

passive solar buildings

active solar heating