HVAC systems are of great importance to architectural design efforts for four main reasons.
- First, these systems often require substantial floor space and/or building volume for Equipment and distribution elements that must be accommodated during the design process.
- Second, HVAC systems constitute a major budget item for numerous common building types.
- Third, the success or failure of thermal comfort efforts is usually directly related to the success or failure of a building’s HVAC systems.
- Last, maintaining appropriate thermal conditions through HVAC system operation is a major driver of building energy consumption.
HVAC System Evolution
The first step in selecting a HVAC system is to determine and document constraints dictated by performance, capacity, available space, budgets and any other factors important to the project. This usually starts with a formal meeting with an architect/owner and understanding his or her requirements.
Owner’s Needs
If the architect is a creator, the customer is a king and his needs and requirements must be met.
Depending on the customer goals, the building and its HVAC requirements have to be designed accordingly. For example take an example of multistorey office building. The complete building may have either a single owner or multiple owners. A single owner normally has a preference for a central plant, as the quality of air conditioning is far superior and life expectancy is higher. The operation and maintenance costs are also lower than a floor-by-floor system. In addition the owners can opt for an intelligent building by incorporating a building management system (BMS).
This will enable the owner to derive benefits of optimal utilization of the air conditioning plant. A multiple owner facility requires a system, which provides individual ownership and energy billing for which a floor-by-floor air conditioning system using packaged units or split units is most suited subject to economics of space and aesthetics.
Another important requirement is the normal working hours of the user/users. Some users may have different working hours or different timings. Some areas such as computer rooms may need 24-hour air conditioning. Other areas may have special design requirements. Due to such multiple requirements many engineers prefer a “hybrid system” which is a combination of a central plant and packaged units/split units. For example, a hotel may use packaged unitary air conditioners (or fan coil units served with air-water central system) for the individual guest rooms, roof top units for meeting rooms/restaurants, and a central plant system for the lobby, corridors and other common spaces. Such systems offer high flexibility in meeting the requirement of different working hours and special design conditions.
While HVAC engineer manages the system design the architect retains control of the complete building product. The type of system selected is determined by HVAC designer’s knowledge of systems. Architect must also understand the basics, system objectives, the role of key system components, the type of systems that are available and what such systems can and cannot accomplish. Most customers may not understand HVAC design aspects; their benefits and limitations and it is the architect’s/ HVAC engineer’s responsibility to guide and advise the best option. For HVAC engineer the customer may be an architect whose customer may be the building owner.
What Influences HVAC design?
Investment in a building project entails significant capital investment and associated costs over the economic life of the project. It is a mistaken notion that the buildings costs have to be expensed once. The buildings like any other industry have running expenses in a way that they consume lot of energy and require water & disposal facilities that accounts for significant recurring costs. The HVAC systems often are very large and are responsible for a large portion of a building’s first cost and operating cost.
Every building is unique. For instance residential apartments, shopping complex, office complex, hospital, hotel, airport or industry; all have different functional requirements, occupancy pattern and usage criteria. The geographical location of the building, ambient conditions, indoor requirements, building materials, dimensional parameters, aesthetic requirements, noise and environment issues need careful evaluation. The HVAC design and selection must be customized to meet all these requirements.
Each solution begins with an assessment of the owner’s business needs for HVAC, architect’s vision, requirements of the facilities manager, combined with a review of the HVAC system itself, be it existing or planned.
Design aspects for HVAC System
HVAC systems is an important part of the building construction budget, account for a major portion of a building’s annual energy consumption, often require substantial space allocations and contribute to interior environment that is critically evaluated by the building occupants and the users. Everyone cares about cost! But the wise customer lays down a list of minimum requirements and then negotiates. Mostly customer goes for price only and skips on right equipment and design specifi cations. The selection process could be chilled water system or direct expansion system, the design of HVAC systems is mainly related to various parameters, including but not limited to the factors listed below.
Details of architecture
-Structure, orientation, geographical location, altitude, shape, modulessize & height
-Purpose of the building, area classification, occupancy and usage patterns
-Ratio of internal to external zones, glazing, plant room sitting, space for service distribution
-Climate and shading, thermal insulation, passive climate control, relationship with adjacent buildings
-New or existing building, renovation or extension project, retrofitting or new equipment
-Plant and system design to match the characteristic of the building and the need to meet the needs (known and unknown) of the ultimate occupants.
Details of Space allocation
-Floor space and clear heights to accommodate HVAC plant, equipment, distribution and room elements
-Shaft spaces available for routing ducts/pipes
-Location and size of structural columns and beams, clearance through steelwork, position of reinforcing rods
-Ceiling height, clearance between suspended ceilings and beams
-Foundation and supports requirement, permissible loadings
-Location of obstructions that may be in the route of air-conditioning services, particularly ductwork.
Details of building construction
-Materials and thickness of walls, roof, ceilings, fl oors and partitions and their relative positions in the structure, thermal and vapor transmittance coeffi cients, areas and types of glazing, external building finishes and colour as they affect solar radiation, shading devices at windows, overhangs, etc., as they reduce solar radiation and light transmission, building mass, particularly as it aff ects thermal capacity
-Sound and vibration control requirement, relation of airconditioning equipment to critical areas
-Co-ordination with other services (e.g. electrical and plumbing work), use of service shafts, ducts and equipment rooms to best mutual advantage.
Building regulations
-Government and local regulation on occupancy & safety classification
-Regulations of Public utilities on electrical wiring, power usage, water supply and drainage
-Health and Safety regulations on indoor air quality, ventilation air quantities, noise control, electrical, fuel, insulation and other hazardous materials
-Local fire authority regulations and smoke removal systems
-Insurance company regulations.
Miscellaneous Requirements
-Accessibility for installation of equipment, space for maintenance;
-Location of fresh air intakes and exhausts (to avoid short-circuiting and contamination);
-Location of fire zones and fire walls (position of fire dampers);
-Acceptable noise level: space available to house equipment and its location relative to the conditioned space
-Indoor & outdoor equipment preferences
-Acceptability of components obtruding into the conditioned space.
Building Aesthetics
-Architectural characteristics of space,
-Reflected ceiling plans: Integration of air distribution devices in ceiling to harmonize with lighting layout, fire sprinklers, detectors, communication systems and ceiling design
-Size and appearance of terminal devices.
System considerations
-Thermal influence – Solar gain, ambient conditions (dry bulb/wet bulb temperatures), indoor condition (dry bulb/relative humidity) requirements, heat gain from people, artificial lighting, equipment and machinery, ventilation air load
-System behaviour – Thermal comfort, indoor air quality, cooling/heating peak loads, partial loads, average load conditions and pattern of variation, capacity of the system
-Load behaviour – Sensible/latent heat balance, Load diversity, and system response related to thermal capacity storage effects
-Psychrometric processes – engineer prefer to carry out their calculations on a psychrometric chart of the aspects include actual vapor pressure; relative humidity; moisture content; specific enthalpy; specific volume (or humid volume) and dew point.
-Operation Philosophy- Hours of system operation;
-Control Systems- Zone or individual control, system response and lags, permissible tolerances and time system, direct digital controls, sequence of operations and control logic
-Energy Efficiency-Energy availability, level & pattern of energy use, type of system, peak load and part load energy performance, Variable speed drive, energy effi cient equipment, building management systems, economizer controls, zoning requirements
-Control and operational requirements – supervision, records, type of adjustment and regulation, hours of operation, summer/winter changeover, day/night and weekend operation, high/low limit protection, frost protection, fi e protection, special control areas (e.g. computer rooms, executive offices);
-Redundancy- Spare & standby requirements, equipment configuration
- Technology features – Humidification/dehumidification requirements, Air purity, Special acoustic treatment, fire protection & smoke management; Water service – capacity, pressure, maximum temperature, chemical analysis (choice of materials), water treatment;
– Commissioning and testing of the completed plant and the adjustment to ensure that it operate as designed in all respect. It is a matter of increasing importance, as components become more sophisticated, more packaged and thus less susceptible to any level of repair.
Financial Consideration
-Capital cost
-Operating cost (fuel, power & water)
-Maintenance & consumables cost
-Replacement costs
-Upgrading costs
-Equipment failure costs
-Labour costs
-Insurance costs
-Interest on capital and depreciation
-Return of investment (ROI)
-Life cycle analysis.
Conclusion
Costs can often be influenced by the owner’s/company’s insurers and risk managers. Successful HVAC systems are the key to successful buildings. Proper selection of air-conditioning services and choice of the most effective system is the foremost application consideration. This includes primary influence from the architect. It is important to understand the characteristics of the building envelope, functional requirements and desired environmental conditions. Each solution begins with an assessment of the owner’s business needs, architect’s vision and the requirements of the end user, combined with a review of the HVAC system itself, be it existing or planned.
