Building science engineers have many tools to help diagnose building performance problems. Most are quite simple — a gauge for measuring crack widths, a smoke pencil to locate air leakage, a probe to determine moisture content. However, many building performance problems are cyclic, and may appear or disappear depending on changes in the exterior and/or interior climates. In such cases, the simple tools are not sufficient, and long-term monitoring is needed to determine exactly what is causing the building problem.
There are many different types of sensors that will collect data over an extended period of time, anywhere from a few days to a year or more. The parameters typically measured include temperature, relative humidity and pressure. Here’s a look at three case studies where long-term data collected from a sensor was used to help solve building performance problems:
Investigating excessive condensation using a surface temperature sensor
Excessive condensation and frost was occurring on the doors of a building, so surface temperature sensors were taped to the surface of various locations on the interior of a typical door as well as the wall surrounding the door.
The sensor used can record and hold up to 2,048 measurements, and can be programmed to record at any interval. So, for example, it will record every five minutes for a week or every hour for 85 days. The cost of the sensor is approximately $60, with a one-year life expectancy. To download the information, the sensor is snapped into an adaptor that is then connected to either a USB or Ethernet port on a computer.
The recorded temperatures were correlated to the exterior temperature, and the data was used to prove to the door manufacturer that there was a problem with the thermal resistance of its door.
Investigating mould growth using a temperature/relative humidity sensor
A unit in a high-rise was experiencing mould growth on the interior of the exterior walls. The brick masonry building was approximately 40 years old, poorly insulated, with separately metered electric heating and newly replaced windows. No other units in the building were experiencing the same problem. A combination temperature/relative humidity sensor was installed in the unit for a month in the winter to try to determine why this particularly unit had a problem.
The sensor used will record 16,000 readings, meaning it can record for 27 days every five minutes or almost a year every hour. The sensor costs approximately $90 and the replaceable battery has a life of two years. The sensor incorporates a USB connection in its construction to allow the data to be downloaded directly to a computer.
The collected data was used to determine that during the day, the temperature in the unit dropped and the humidity increased such that the interior wall temperature fell below the dew point temperature of the air. The dew point is the temperature at which moisture will condense out of the air at a given relative humidity level. The moisture on the wall surface then provided an environment conducive to the growth of mould.
It turned out that the residents were turning the heat off during the day when they were not home in an attempt to reduce their energy costs. With these findings, it was possible to convince the owners that leaving the heat on would prevent further mould growth.
Investigating water penetration using pressure taps
A brick veneer high-rise in Ottawa was experiencing water penetration. Veneer walls incorporate an air gap behind the exterior cladding, whether it be brick, siding or precast concrete. When the wind blows on a building, it creates a positive pressure on the wall, which pushes rainwater inwards. The intent of the air gap is to create a “pressure break” so that should rain get past the exterior cladding, it is not pushed further through the wall; instead, gravity drains the water down the inside face of the veneer to flashing that directs the water back to the exterior.
Another consultant had diagnosed the problem in the Ottawa building as a positive pressure difference across the air gap that was forcing water to penetrate through the walls to the building interior. That consultant’s solution was to remove all the exterior brick, apply waterproofing to the exterior of the back-up wall (the portion of the wall on the inside of the air gap), and then reinstall the brick. The total cost was projected at well over $1 million.
To measure the pressure difference across the veneer and across the air gap, pressure taps were installed. A pressure tap is simply an open-ended plastic tube that is connected to a manometer, which is a device that converts the air pressure in the tube to an electric signal that can be recorded by a data logger for later downloading to a computer.
Pressure taps were installed on the exterior face of the wall and on both sides of the air gap. Measurements were recorded over several months to ensure various wind conditions were examined. This proved that there was no pressure difference across the air space, and that the problem was actually that the flashings were not continuous, allowing water to seep into the interior at floor levels. The cost to repair the flashings was a fraction of the cost of the repair proposed by the other consultant.
The sensor and measurement options presented here are simple, inexpensive solutions. More expensive sensors are available that can wirelessly transmit data in real time, without the need to manually download the information. Experience suggests that, while building owners expect long-term monitoring to be costly, the information gained can allow a building science engineer to design a far more economical solution to the problem, with savings that can outweigh the cost of the monitoring.
Dale D. Kerr is chief operating officer and a technical specialist at Pretium GRG Building Engineers. She can be reached in their Newmarket office at (800) 838-8183, or through Pretium Anderson’s offices in Toronto, Burlington and the Waterloo area.