The HVAC Life Cycle Cost Breakdowns
HVAC system design, construction, and ongoing adjustments require large capital investments. Yet, current HVAC system design practices often do not meet an owner’s expectations for energy or maintenance efficiency, nor occupants’ requirements for comfort. Without HVAC design optimization, even HVAC systems in sustainable buildings with extensive commissioning may fail to meet predicted energy efficiency and suffer deteriorating energy and maintenance performance over a short period. A Life-Cycle Performance Assessment will allow a HVAC system to be selected and sized for the whole life cycle performance, not just start-up performance.
HVAC design optimization for life-cycle performance is an engineering practice that considers a system’s energy and maintenance performance and occupant impacts, throughout the life of the system. This practice can produce overall construction savings of up to 5%* and annual operation savings of over 50%*, as well as contribute to increased occupant productivity. For most buildings, sustaining HVAC system performance throughout the life of the system has proved elusive. As such, long-term efficiency and performance must be addressed at the beginning of a project as part of an integrated, or “whole building”, approach so that the HVAC design process both includes and optimizes long-term operating and energy performance strategies.
A. Process for Optimizing HVAC System Life-Cycle Performance
HVAC system life-cycle performance optimization begins at the very beginning of a project. Close team collaboration is required to develop the client’s short, medium, and long-term goals, objectives, and expectations related to:
Indoor thermal comfort for occupant effectiveness (which includes considerations such as ambient temperature control, radiant temperature control, humidity, ventilation, air cleanliness and purity, lighting quality, visual stimulation, sound control and acoustics);
Functional performance of HVAC systems; and
Performance requirements for present and long-term operation of HVAC and energy systems.
Actual long-term operating characteristics can be very different from initial operating characteristics; and long-term needs can be very different for each building situation, particularly when long-term goals are introduced.
These performance expectations must be written down plainly in the design documents so what the clients want cannot be misinterpreted or misrepresented. These Detailed Design Intent Documents (DDI) are developed early in the design process and include a detailed narrative of the performance-based design intent (the client’s immediate and long-term goals, objectives, and aspirations, including HVAC performance expectations and requirements) with a basis of design and details of system selections (the design team’s detailed responses in system and component selection and sizing) as they relate to long-term operation and maintenance requirements. Every how and why of system performance criteria and selection is documented for the design, construction, and operating personnel. The DDI takes into account future foreseeable changes and modifications in the building usage and describes how the proposed systems will work through these scenarios. The DDI becomes the living document that chronicles the building planning, design development, construction, operation, modifications, and performance.
The next step in the HVAC life-cycle performance optimization process is providing supervision throughout HVAC system design and installation, and during testing, balancing, start-up, and turnover. See also Project Management Project Planning, Delivery and Controls. Revisiting the project throughout the first year’s operation ensures that the HVAC system is finely tuned to operate optimally through all the seasons.
In this way, HVAC life-cycle performance optimization provides continuity throughout the design, construction, and operation stages of the building, and should be an ongoing process throughout the life of the building, providing annual certification where necessary.
To measure the effect of a new indoor environment on client satisfaction, an evaluation of occupants’ effectiveness/satisfaction in their current space(s) is necessary to establish a baseline for comparison. A post-occupancy evaluation of facility performance and user satisfaction with the new environment will determine if the client’s expectations for improvement have been met and, if not, what needs to be adjusted.
Degradation of HVAC system performance during the first five years of a building’s operation is a major problem facing most buildings. HVAC design optimization assures that system and component selection are made with long-term performance as one of the parameters. This means the systems’ operation and performance expectations will be maintainable throughout the life of the building.
If done correctly, HVAC systems, in combination with lighting and acoustics, can increase occupant effectiveness by over 25%*, which can pay for a portion—if not all—of the construction costs. E-Source reports that just one year of the salaries of workers in a typical office building equals twice the entire cost of the building and 100 times the annual electricity bill. Also, a productivity increase of 10% creates a 30% increase in a company’s bottom line.
B. Features of HVAC Life-Cycle Performance Optimization
HVAC life-cycle performance optimization differs from traditionally practiced HVAC design in three primary areas:
A Detailed Design Intent. Developing a written Detailed Design Intent as standard practice will improve communication between owner, designers, contractors and operators many times over. Because a detailed explanation is required for any of the decisions that are made, every answer is totally thought out. This document helps reduce construction costs, operating costs and increases occupant performance.
Long-term operational considerations. Including minor modifications, maintenance and operational efficiencies over the longer term. These will often cause a change in system selection because systems that are generally chosen by other methods will not compare as favorably to long-term and modification-friendly requirements. These help reduce long-term operating and modification costs considerably.
Detailed Post-Occupancy Evaluation, aka Facility Performance Evaluation. The standard measurements of air-flow in ductwork and temperatures of air and water systems only indicate a small part of the performance of a buildings HVAC system. Building Occupancy Data Analysis is a standard way of assessing occupant reaction to the indoor environment.
C. Three Common Sense Rules of Thumb of Long-Term Maintenance
To understand long-term operating characteristics it is important to understand the common sense rules of thumb governing long-term maintenance—because systems that are not maintained correctly cannot perform at their peak. These rules of thumb were what the old time steam designers considered essential design strategies for maintenance, but have since been forgotten by mechanical system designers.
The Rules of Thumb of Long Term Maintenance are:
All moving parts must be in plant rooms.
If it is not easy to maintain; it will not be maintained.
Maintenance manpower and effort will decrease over time.
The three rules of thumb above were used by many design/construct HVAC engineers in the years prior to World War II (WWII). As HVAC systems became much more sophisticated after WWII, design engineers became separated from construction, and construction became separated from maintenance, resulting in three degrees of separation from design to operation. Consequently, long-term maintainability became entirely the problem of the operating and maintenance staff. The case study below illustrates how application of the rules of thumb plays out for various HVAC systems.
To view a more extensive summary of HVAC Life Cycle Costs, view this article on the Whole Building Design Guide.