For buildings to operate effectively and save energy they must be commissioned properly and operational problems must be detected and diagnosed. Collection of sensor and control data is essential to this process. Likewise, the analysis of this data with effective tools is critical to performing this work in a cost effective manner. In general, the buildings industry lacks consistent methodologies or protocols that make this process of data collection and analysis effective and efficient; the practitioner usually develops his own techniques on a more or less ad hoc basis. Also lacking is a consistent way to accumulate data over time from many projects that could be helpful to the analysis of a particular system. To help remedy this situation (and to serve as an example of this concept) the Center for Environmental Design Research (CEDR) at UC Berkeley developed diagnostic protocols and a software "toolkit" (UCB AHU Toolkit) to help practitioners identify and rectify problems with large built-up air handling units (AHU). [Carter 1998, Webster 1998, 1999]. These tools and protocols rely on short term monitoring and a set of supporting spreadsheet based tools to screen for problems in AHUs and to conduct more in-depth diagnostic studies for problems found.

The work described herein is an extension of the previous work and comprises Task 2.2.1 of Project 2.2 of the High performance Commercial Buildings Systems (HPCBS) project. The goal of Project 2.2, Monitoring and Commissioning for Existing Buildings, is to facilitate the development of diagnostic procedures and commissioning tools needed by owners, operators and the commissioning industry to perform and analyze test results and operate buildings efficiently.

Underfloor air distribution (UFAD) is an innovative technology that uses the underfloor plenum below a raised floor system to deliver space conditioning in offices and other commercial buildings. The use of UFAD is increasing in North America because of the benefits that it offers over conventional ceiling-based air distribution.

This paper reports on a modeling study to investigate the primary pathways for heat to be removed from a room with underfloor air distribution (UFAD) under cooling operation. Compared to the standard assumption of a well-mixed room air condition, stratification produces higher temperatures at the ceiling level that change the dynamics of heat transfer within a room as well as between floors of a multi-story building. A simplified first-law model has been used to estimate and compare the relative magnitudes of the heat being removed from a room through two primary pathways: (1) heat extraction via warm return air exiting the room at ceiling level or through the return plenum and (2) heat entering the underfloor supply plenum either through the slab from the floor below or through the raised floor panels from the room above. Surprisingly, it is shown that up to 40% of the total room cooling load is transferred into the supply plenum and only about 60% is accounted for by the return air extraction rate. The implications for the design and operation of UFAD systems are discussed.

The use of an underfloor plenum to deliver conditioned air directly into the occupied zone of a building is one of the key features that distinguish underfloor air distribution systems from conventional ducted overhead systems. This paper describes the development, validation, and application of a computational fluid dynamics (CFD) model for predicting the airflow and thermal performance of underfloor air supply plenums. To provide validation data for comparison with the CFD model, a series of experiments in a full-scale underfloor plenum test facility were carried out. The results of the experiments and comparison with the model predictions are described for the major variables, including plenum airflow patterns and velocities, plenum air temperature distributions, and heat exchange between the exposed concrete slab, the underside of the raised floor panels, and the supply air as it flows through the plenum. The validated CFD model was used to perform additional simulations to investigate the impact of plenum inlet design parameters (location and airflow direction and velocity) on the plenum heat gain and temperature distribution. Implications for the design and operation of underfloor air supply plenums are discussed.

More than 130 underfloor air distribution (UFAD) systems are installed in North America today, and that number is growing. In comparison to classical displacement ventilation (DV) systems that deliver air at low velocities, typical UFAD systems deliver air through floor diffusers with higher supply air velocities. Ina addition to increasing the amount of mixing (and therefore potentially diminishing the ventilation performance compared to DV systems), these more powerful supply air conditions can have significant impacts on room air stratification and thermal comfort in the occupied zone.

Tests were conducted to determine the impact of room airflow and supply air temperature (SAT) on the thermal stratification in interior spaces, and the effect of blinds in perimeter spaces for UFAD systems. Room airflow was varied over the range of 0.7-5.1 (L/s)/m^2 (0.3-1.0 cfm/ft^2) and SATs over 15-19°C (60-67°F) for constant nominal interior heat input of 55-59 W/m^2 (5.2-5.5 W/ft^2). Results show that spaces can be highly stratified when the airflow is reduced for a given load. When SAT is varied, the shape of the temperature profile does not change; it only moves to higher or lower temperatures. Perimeter space tests conducted at a heat load of 116 W/m2 (10.7 W/ft^2) and constant room airflow of 5.1 (L/s)/m^2 (1.0 cfm/ft^2) with blinds opened or closed showed that room load is reduced when blinds are closed due to bypassing of window gains directly to the ceiling return via a convective plume.