Introduction

The modern day definition of air-conditioning was created in the early 20th century based on

the vision and works of Hermann Rietschel, Alfred Wolff, Stuart Cramer, and Willis Carrier.

Cramer, a textile engineer in North Carolina, is credited with coining the phrase "air-

conditioning" in 1906. In 1908, G.B. Wilson developed the first holistic definition of what

air-conditioning encompasses.

The Original Definition of Air-Conditioning

To maintain a suitable degree of humidity in all seasons and in all parts of a building

To free the air from excessive humidity during certain seasons

To supply a constant and adequate supply of ventilation

To efficiently wash and free the air from all micro-organisms, effluvias, dust, soot,

and other foreign bodies

To efficiently cool the air of the rooms during certain seasons

To either heat the rooms in winter or to help heat them

To combine all the above desiderata in an apparatus that will not be commercially

prohibitive in first cost or cost of maintenance

(Source: Nagengast, B., 1999, "Early Twentieth Century Air-Conditioning Engineering",

ASHRAE Journal, March (p.55)

Though he did not actually invent air-conditioning nor did he take the first documented

scientific approach to applying it, Willis Carrier is credited with integrating the scientific

method, engineering, and business of this developing technology and creating the industry we

know today as air-conditioning.

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Description

Today's HVAC&R engineer, or mechanical engineer of record (MER), continues to be a

steward of the basic discipline issues identified by Mr. Wilson nearly 100 years ago. Roles

have expanded, though, to address more modern quality of life issues. ASHRAE offers the

current vision of the MER's stewardship responsibilities: to improve the quality of life by

helping keep indoor environments comfortable and productive; by helping to deliver healthy

food to consumers; and by helping to preserve the outdoor environment.

As part of a holistic controlled environment design solution, the MER is responsible for

addressing seven major processes. These are:

1. Heatingthe addition of thermal energy to maintain space or process conditions in response to thermal heat loss

2. Coolingthe removal of thermal energy to maintain space or process conditions in response to thermal heat gain

3. Humidifyingthe addition of water vapor to maintain space or process moisture content

4. Dehumidifyingthe removal of water vapor to maintain space or process moisture content

5. Cleaningthe process of removing particulate and bio-contaminants from the conditioned space.

6. Ventilatingthe process of providing suitable quantities of fresh outside air for maintaining air quality and building pressurization.

7. Effectivenessthe process of achieving the desired thermal energy transfer, humidity control, filtration, and delivery of ventilation air to the breathing zone of the occupied

space in accordance with required needs.

It is important for the MER to be involved early in the project, even as early as the

programming stage, so that mechanical system space issues and facility energy budgets can

be evaluated and integrated into the design process before building construction elements,

configurations, and orientations are finalized (see also WBDG High-Performance HVAC). A

few critical issues that need to be considered early are:

Financial Focus: Will the project be a code minimum type facility or will total

ownership cost perspectives be considered that balance capital first costs against long-

term ownership and operating costs?

Owner Sophistication: The MER needs to understand the abilities of the owner and

keep these in mind as mechanical system architecture issues are considered. The best

of design solutions aren't much good if operators do not understand how to correctly

operate or control the equipment.

Operations and Maintenance: No matter what level of system complexity is applied, it

is imperative that suitable space be made available for equipment without

compromising performance or maintenance access. A good MER will understand the

requirements published in equipment installation manuals and focus on providing

prescribed minimum service and operating considerations in the planning of a facility

layout.

Before any equipment selections can be finalized, the MER will need to perform a thermal

load calculation for the developing facility based on internal and external influencing factors.

In many cases, this activity will be expanded to include analysis of comprehensive energy

models. These models will foster dynamic integration opportunities whereby the design team

and owner can evaluate the impacts of trade-offs between facility construction elements,

mechanical system alternatives, and available operating efficiencies. Load calculations can be

utilized for any or all of the following design activities:

A. Defining the basic load dynamics B. Evaluating solution alternatives via life-cycle analysis C. Optimizing system performance D. Selecting final HVAC equipment E. Establishing energy budgets for owners F. Verification of proposed equipment performance G. Commissioning Design Intent for seasonal comparison

The MER will be responsible for securing/developing the following fundamental information

from the Owner and design team members:

Basic Load Calculations:

o Establish summer/winter design weather conditions paying particularly close

attention to regional weather issues and impact on

humidification/dehumidification considerations.

o All elements of the building envelope must be identified so that thermal

energy loss/gain can be determined. Reference should be made to ASHRAE

Standard 90.1 for regionally documented envelope construction minimum

thermal quality considerations.

Orientation of walls and roofs need to be defined so that sun angle

impacts can be evaluated.

The composite construction of all walls, roofs, and floors needs to be

defined so that thermal transfer calculations can be performed. This

information will also be useful when a dew point analysis is performed

on the envelope.

Thermal mass and color of walls and roofs need to be defined so that

thermal time lags and radiation absorption can be evaluated.

Fenestration U-values and solar heat gain coefficients need to be

defined.

External/internal shading provisions need to be defined that may

impact fenestration heat gain.

o Lighting:

Lighting densities and ballast loss factors need to be mapped per

individual space. Maximum densities are identified for individual

space types in ASHRAE Standard 90.1.

Opportunities to capture natural light (Daylighting) and apply

occupancy sensing techniques to reduce light heat gain need to be

explored.

o Basic internal sensible heat gain allowances for receptacle loads need to be

established.

o Miscellaneous sensible and latent heat gain values need to be identified for

special circumstances.

o People contributions:

The total number of people and the occupancy usage profiles need to

be established.

The activity levels of people need to be identified.

o Ventilation:

For a given space, the area factor and people factor ventilation rate

components need to be calculated per ASHRAE Standard 62.1.

Depending on HVAC system architecture employed, critical space

calculations may need to be performed to adjust ventilation quantities

to ensure adequate outside air is being provided to occupied spaces

during all system fluctuations.

Calculate all building exhaust requirements and compare to minimum

required outside air ventilation rates. The overall impact of building

pressurization dynamics must be evaluated for the facility, for seasonal

conditions, and for regional locations. The MER must fully understand

how moisture and thermal gradients work with the building envelope

construction and what influence infiltration/exfiltration has on

condensation potential.

o Basic system zoning:

Identify spaces and zones.

Establish summer/winter design temperature set-point conditions and

dead-band ranges per thermal comfort recommendations of ASHRAE

Standard 55.

Energy Modeling:

o Establish realistic average weather profiles for project location.

o Define realistic 24-hour usage profiles for the entire calendar year taking into

account workdays, weekends, holidays, etc.

o Obtain current rate structures from utilities.

o Define accurate equipment power consumption paying particular attention to

part load efficiencies.

Life-Cycle Analysis:

o Define capital cost impacts of equipment and system alternatives.

o Determine client applicable time value of money evaluation parameters.

o Determine accurate maintenance costs for equipment and system alternatives.

Integrated Design Process (See also WBDG High-Performance HVAC)

Once the facility thermal issues are identified, the MER will be faced with application

decisions to find appropriate, constructible, controllable, affordable, and maintainable

HVAC&R solutions. These solutions must be integrated and coordinated with parallel design

and planning activities of fellow design team members. While not totally encompassing, the

following discipline considerations need fundamental attention:

Architectural Interaction:

Impacts By Impacts To

Equipment room locations, accessibility, and size

Location and appearance of air distribution devices

Floor to floor height, depth of structure, ceiling height,

and available utility space in ceiling cavity

Component aggregation and location of building

envelope elements

Location of Life Safety features such as fire and smoke

rated construction and the impacts on HVAC

constructability

Location and construction of noise sensitive areas

Selection of interior finishes and VOC impacts.

Location of

equipment

Orientation of the

building

Structural Engineering Interaction:

Impacts By Impacts To

Type of construction: steel,

concrete, wood, etc.

Foundation design

Fireproofing techniques

Seismic criteria

Location, weights, and

support/attachment of equipment

Civil Engineering Interaction:

Impacts By Impacts To

Location of site utilities

Siting and landscaping impacts on thermal

loads and noise trespass

Size and location of utility

connections

Electrical Engineering Interaction:

Impacts By Impacts To

Size of available power service

Layout of design

Gen-set ventilation, heat removal, and

fuel support requirements

Location of electrical infrastructure:

switchboards, panels, feeders, etc.

Equipment power requirements

Coordination of power hook-up

and disconnecting means

Coordination of Fire Alarm shut-

down and smoke detectors

Location of duct, pipe, and air

distribution

Plumbing Engineering Interaction:

Impacts By Impacts To

Type and capacity of heat generation

plant for hot water heating

Location of plumbing infrastructure:

equipment, piping, etc.

Make-up water requirements and

backflow protection

Condensate drainage disposal

requirements

Location of duct, pipe, and air

distribution

Fire Protection Engineering Interaction:

Impacts By Impacts To

Fire pump ventilation, heat removal, and fuel

support requirements

Location of sprinkler and standpipe

infrastructure: equipment, piping, heads, etc.

Location of duct, pipe, and

air distribution

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