Evaluating the interior environmental performance of an existing office building

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This article showcases an investigation of the interior environmental performance of an existing office building, the Deakin Callista Offices. The article also includes the 'before and after' evaluation of the newly retrofitted HVAC control system.

Summary

The exterior of Deakin Callista Offices, Geelong Victoria.
Source: MABEL

This project showcases the investigation of the interior environmental performance of the Deakin Callista Offices (pictured above), a refurbished and recycled Woolstore building on the Deakin University Waterfront Campus in Geelong Victoria. After several instances of occupant discomfort and complaints, the management of the building decided to engage the Mobile Architecture and Built Environment Laboratory (MABEL) to investigate the interior environmental performance as well as to perform an occupant survey in February 2005. The following is a brief summary of the findings and the 'before and after' retrofitting of the HVAC control system. It is also an example of what buildings owners and management can get accomplished for their buildings through rigorous worthwhile investigation and research.

The Deakin University Waterfront Campus - Callista Offices

This project showcases the refurbishment and recycling of a Woolstore building on the Deakin University Waterfront Campus in Geelong Victoria. At the inception of the Deakin Callista Offices, to be located at the top level of the Ford Museum building, the Built Environment Research Group (BERG) was called upon to provide simulation studies regarding daylighting and energy consumption performance for the 1000m² space.

The advice on daylighting with regards to glazing selection, size and location as well as control was accepted and proved to be a success, while the information on HVAC sizing, solar shading, and heating, ventilating and air-conditioning concepts were neglected. After several instances of occupant discomfort and complaints, the management decided to engage the Mobile Architecture and Built Environment Laboratory (MABEL) to investigate the interior environmental performance of the Deakin Callista offices as well as to perform an occupant survey in February 2005.

Floor Plan with accompanying pictures of the office interior
Source: MABEL

This initial survey indicated that the occupants were mainly concerned about their thermal discomfort. At around this time the Australian Greenhouse Office were looking for 'Before and After' case study with the MABEL facility. MABEL was also approached by the Bauer Optimising Technologies company who wanted to prove the performance and capabilities of their product, claiming superior HVAC control. The following is a brief summary of the findings using the MABEL facility as well as the 'before and after' retrofit. It is also an example of what buildings owners and management can get accomplished for their buildings through rigorous worthwhile investigation and research.

Project Overview

An important and major part of the project was to measure the energy use and consumption for the newly installed control system over that of the original. Given the circumstance that the Bauer control system, could not be completely implemented because of the central chiller plant serving additional building zones, a compromise needed to take place, and the Bauer system needed to apply the chilled water temperature as available. Nevertheless substantial savings are indicated from this study. The primary savings would be in the total energy costs to produce chilled water for cooling purposes which were found to be on the order of 60% less during summer conditions. Further savings are in the variable fan speed drives compared to the original constant drive fans. Here again, almost 50% savings occurred from that of the original system. The other important realisation is that several of the existing air handling units (AHU's), typically used to treat the space, were turned off and not required to maintain conditions during the Bauer controlled periods.

AHU Layout: floor plan (left); Chilled water demand of the control system (right).
Source: MABEL

Control technicians (of the conventional systems) disputed that the readings on the graph (to the right above) were accurate since they registered 100% chilled water supply demand for the original system. It was discovered later that these technicians spent 2-3 days with variations in their conventional control strategy to attempt better savings than the original system. The conclusion was that they could indeed provide a reduction in chilled water demand - but not with only two air handling units running. As a result, the graph was understood and accepted.

These findings merit further investigation with the newly installed system for other buildings, especially newly designed systems where up to a 40% reduction in system sizing could take place.

One of the planned investigations by MABEL was the claimed increases in comfort for the east façade of the building. Such was investigated with the Façade Analysis Meter as well as the thermal imaging camera.

Façade Analysis Meter (left); Exterior Façade Thermal Imaging (Temperature)(right).
Source: MABEL

The faced meter showed extraordinary results in the differences between the Bauer optimised controlled comfort conditions with that of the original control. These results are presented below beginning with the weather conditions, results of the radiant asymmetry probe and glass surface temperature, as well as the resulting Predicted Percentage Dissatisfied (PPD).

BAUER Optimised Control (left); Original Conditioned Space (right).
Source: MABEL

The above two charts present the measured weather at the site under both Bauer controlled (left) and original controlled (right) conditions. Note: there are two totally different days indicated here.

BAUER Optimised Control (left); Original Conditioned Space (right).
Source: MABEL

The radiant asymmetry (indicated in green) is shown for both Bauer conditioned and original conditioned spaces. It is interesting to note that the radiant component reaches the same intensity on both days. However, in the forthcoming comfort 'vote' (predicted percentage dissatisfied - PPD) there is an indication of better comfort under the Bauer controlled condition. Also, it is noted that the surface temperature does not rise as high as under original conditioning.

The Predicted Percentage Dissatisfied as well as the Operative Temperatures: for Bauer (left) and Original (right) HVAC controlled conditioning systems.
Source: MABEL

The above two graphs indicate the comfort achieved at a 1.0 meter interior distance from the east façade. Although the day is different with respect to external temperature there remains a significant difference between the two levels of comfort.

Comfort Conditions (PPD) and Interior Air Temperature: at the locations of the Comfort Carts indicated on the floor plan at the beginning of this report.
Source: MABEL

Note that there are several intervals of the PPD which register above the 20% dissatisfied. These points were checked and were noted to be 'slightly cool' during a hot summer period where cooling would have been desired. In other words, contrary to what might be expected, the 'discomfort' was not due to overheating.

Comfort Conditions (PPD) and Interior Air Temperature: at the locations of the Comfort Carts indicated on the floor plan at the beginning of this report.
Source: MABEL

Under a hot summer exterior week the newly installed system provided 100% fresh air maintaining, in a fairly crowed office, CO2 levels below 650 ppm. At the same time occupants experienced a significant reduction in excessive HVAC background noise due to the quietness of the new control (see figure below). There is on average about a 6 dB reduction in background noise levels.

Office Interior CO2 Levels
Source: MABEL

Energy Analysis Summary

Due to the 'lumped' metering approach within the university system it is difficult to make an exact assessment of the energy breakdown between HVAC, lighting and other plug loads. At best an assessment is made here between the 'typical' office HVAC consumption of 65% of the total energy load with that of 'other' loads including lighting. The table below provides an estimate only of two totally different years of occupancy. In 2004 the Callista offices were newly occupied and operated under the original system. In 2006 the Bauer Optimised Control system was fully implemented. It is estimated that there would be about a 70% total energy reduction in the HVAC operational energy under the Bauer system. Given the fact that there are four less Air Handling Units in operation this is believed to be a reasonable estimate.

Conclusion

The installation costs for this retrofit were on the order of $65,000 and do not yield a terrific payback period as presented here. Unfortunately this installation was complicated by other factors which were not typical to retrofitting. Nevertheless, the learning from the study introduced an HVAC system and conditioning strategy which is being introduced into other campus buildings. Presently, the university has already capitalised on saving an entire chiller in a new project through the application of this control technology.

For more information about this project, visit http://www.mabel.com.au