Purdue University

Wetherill Air Handler Unit Replacement Study and Design

*Winner of the 2015 ACEC Indiana Engineering Excellence Honor Award*







Wetherill Laboratory of Chemistry, recently dedicated as a national Historic Chemical Landmark, was built in two phases. The eastern third of the building was built in 1930 with perimeter steam heat and tempered outside air (TOA). In 1951, the remaining two-thirds of the building were constructed, again with perimeter steam heat and TOA. However, this time selected non-laboratory spaces were provided with air handlers that used the TOA and well water for cooling, in lieu of chilled water.

Over the years, additional air handling unit systems were added with all air handlers connected to campus chilled water for cooling, but the main make-up air systems remained without cooling.

Applied was selected to first study the building’s current make-up and ventilation needs, and then to study exhaust requirements and options to improve the system.

Supply Air Study
Our study examined the ventilation air system for the building and every air handling system, 75 in all. We found that several occupied spaces and the corridors were being supplied with TOA only and not being cooled in the summer. The completed study recommended all 186,000 CFM of make-up air be conditioned for temperature and humidity control and also recommended a phased construction process with established priorities, as the building will remain operational during the construction periods.

Exhaust Air Study
This study examined the exhaust air system for the building to include all 225 fume hoods. The study found a wide variety of fume hood types and sizes with most fume hoods running at constant volume and. Each fume hood had its own fan in the attic. The completed study recommended a series of roof-mounted exhaust manifolds be installed to reduce the number of fans to be maintained and to set in place the infrastructure for variable volume lab controls. The study also concluded a normal run around heat recovery loop was not viable, but that 100% outside air in the winter could be used to generate campus chilled water.

Phase I
In Phase I, cooling control was added to the tempered outside air systems. In addition, seven air handling units were replaced, either because they needed to be replaced or because they were added to replace outdated fan-coil systems.

Modifications to the chilled water and steam systems were also made, as well as the installation of new air filtration, a new glycol pre-heat system, and a new reheat water system. The chilled water systems serving the tempered outside air systems are being controlled to generate campus chilled water in the winter. The first phase was completed in the winter of 2010 at a cost of $4,000,000.

A heat recovery project was identified to capture cooling from the TOA system in the wintertime and generate chilled water in the building. A peak of 500 tons of free cooling is anticipated, and it will be delivered back to the campus cooling system using the building chilled water circulating pumps. Other forms of heat recovery were investigated, such as hood exhaust heat recovery, but most systems required a distributed heat recovery loop to get to all 75 air handling unit systems, which was not economically sound.

The Phase I project was bid in July 2009 for a construction budget of $3.9 million. Construction was completed in the winter of 2010.

Phase II
In Phase II, five exhaust manifolds were installed on the roof and all of the corresponding exhausts in the areas served were connected to the new manifolds, eliminating the individual fans in the attic. Laboratory Airflow Control Systems were added to the fume hoods where appropriate, and conventional exhaust terminal units were added to the non-laboratory exhaust systems to control the amount of exhaust airflow.

Two critical, failing air handlers were also replaced to keep a basement lab in operation.

The Phase II project was bid in March of 2012 for a construction budget of $4.3 million. Construction was completed in the fall of 2013.