The cost data for the Percent of Transfer

The cost data for the Percent of Transfer equal to 80% corresponds to the space cooling supply airflow of  2,000 cfm. It is noted that the transfer percentages greater than 80% may produce more annual savings and remains a design option. Higher amounts of transfer air than the percent of {Cooling CFM/Exhaust CFM} requires that the makeup air unit have the ability to use return air. A unit with the ability to use return air may be more expensive and complicated to control than a 100% outdoor air unit, the cost of which would offset the marginal economic benefit of using more transfer air. This system design option is allowed by the proposed code. The case where 100% of the exhaust air replacement is available as transfer air allows the designer to use a recirculating conditioning unit without any outside air. This type of system is allowed by the code although it does use slightly more energy than a system using some outside air. This increased energy for 100% transfer systems is attributed to the loss of any free economizer cooling of which there are many available hours in California. The transfer air percentage equal to {Cooling CFM/Exhaust CFM} appears to be a reasonable limitation for all California climate zones to take maximum advantage of economizer cooling with relatively simple and inexpensive equipment and equipment controls