Risk Management Indoor Air Quality (IAQ) Tailoring Lease Specifications www.saif.com
These systems are not optimum from an IAQ point of view. More advantageous are systems with so called “economizer cycles” which are designed to bring in larger and larger quantities of OA when the outdoor conditions are favorable for the use of OA for “free cooling.” These economizer systems, however, go to their minimum OA settings when the outdoor air temperature gets above the maximum delivery temperature for cooling or when it approaches or is below freezing outdoors. More advantageous in some situations, where an analysis of life-cycle costs demonstrates a favorable return on investment, are systems with the ability to recover heat or cooling from the building exhaust system so that even during unfavorable outdoor air temperatures, sufficient quantities of outdoor air can be provided without significant energy penalties.
Therefore, it may be specified that:
Prior to occupancy, testing shall be performed by a qualified registered professional engineer or certified industrial hygienist to confirm that the ventilation system, in its minimum outdoor air setting, is delivering the quantities of outdoor air to representative occupied spaces, as called for in this lease agreement. This certification testing shall be by the Tracer Dilution Method as specified in the American Society for Testing and Materials (ASTM) Standard Test Method E74-83.
Spaces with intermittent or variable occupancy may lag or should lead the hours of occupancy in accordance with the provisions of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 62.1. Certain assumptions may have to be made of occupancy levels, especially if reference to ASHRAE 62.1-2004 is made since this Standard references outside air on a cubic feet per minute (CFM) per person basis.
In this wording, it is the delivery of the outdoor air to the occupied spaces that is stressed, because the quantity of OA entering the HVAC from the outdoors typically does not actually get delivered to the building occupants due to leakage from the supply ductwork and other distribution inefficiencies. Also, it is the minimum outdoor air quantities that are specified because many types of ventilation systems can vary the quantity of outdoor air being drawn into them.
The potential challenge in this situation is that buildings built for a nonspecific tenant will vary in the point in construction where the initial tenant begins to have input into the decision-making process.
One of the problems associated with lease arrangements is that “spec” building, i.e., buildings built on speculation, with no specific tenants under agreement, are typically built with an eye towards minimizing the “first costs” of construction. In this situation, the builder has little incentive to perform “life cycle” costing in his decisions. Unfortunately, this means that the building systems are less likely to include heat recovery for the ventilation system.
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