In The Loop
Radiant system design and performance a key factor in meeting LEED requirements.
February 1, 2013 by Mike Miller
In recent years, more building owners and architects have been increasingly asking for more energy and environmentally friendly designs. This is a good development for our industry as we can be one of the greatest contributors to green building. Some of the best in the trade are already getting into the challenge of providing systems that are more environmentally friendly and energy efficient, while keeping things simple.
It was well over two years ago, when one of those leaders in the industry reached out to me about a project he was working on. The project, a new Toyota car dealership in Welland, ON, aimed to achieve the Leadership in Energy and Environmental Design (LEED) Gold certification. In Canada, it is the Canada Green Building Council ((CaGBC) www.cagbc.org) that administers the LEED brand.
There are various requirements that one would need to fulfill to gain LEED certification, but Strafko Blaskovic of Tri-Mechanical Limited was challenged to ensure that the heating, ventilation and air conditioning side of the project would help meet the requirements.
The system approach was pretty straightforward for this 18 000 sq. ft. building. Due to the very well designed exterior of the building, the heat loss of the building was minimal. The entire building was able to be heated with radiant floor heating alone, even on outdoor design days.
ZONING FOR CONTROL
The building was divided into 12 radiant zones, allowing us to deal with different needs of service and application. Offices, showrooms, parts storage rooms, service bays, board and lunch rooms were all zoned individually. This allowed different temperature requirements to be scheduled to accommodate energy savings during periods of inoccupation. Close to 20 000 ft. of 5/8″ tubing were laid and connected to a total of eight manifolds. The total footprint of the building was insulated and the tubing fastened to wire mesh. The mesh was then elevated using little spacers to allow the tubing to float in lightweight concrete finishing.
Besides the radiant, other major mechanical components include two modulating and condensing boilers, a primary loop complete with pump, air separator, expansion tank, two three-way mixing valves, two variable speed and pressure regulated system pumps, two roof top units and three HRVs. The system is controlled by a direct digital control (DDC) system that utilizes communicating thermostats in each of the radiant zones to provide indoor temperature feedback to the water temperature controllers in the mechanical room, resulting in constant circulation and therefore, the highest energy savings in the most challenging zones at any time. Slab sensors, connected to the room thermostats, are used to limit minimum and maximum surface temperatures. The radiant zoning is provided by thermal loop actuators on multi-zone manifolds, and, two-way thermal zone valves for manifolds servicing single zones.
Two roof top units (RTUs), installed and zoned between the service and labour areas of the building on one, and the offices, boardroom and lunchroom areas on the other, satisfy the two distinct cooling air zones. While there are several radiant zones within each of those two air zones, all thermostats are assigned to its respective cooling air zone and one master out of the group can be selected. This particular system allows for air zone master passing, allowing the master to be moved amongst its thermostats either, with the occupation of rooms, or with ever changing requirements/exposures throughout the day, due to solar gain noticed around the large window areas.
VENTILATION AND IAQ
Apart from a dedicated HRV for the washrooms, the two main air zones are operated with the HRV on constant low speed during building occupation for ventilation purposes. These are overridden to high speed by CO2 sensors in case of indoor air quality (IAQ) concerns when the CO2 rises above 700 parts per million (ppm).
For the majority of the year, the outdoor temperature is cool enough to allow for the building to utilize free cooling, via bypass dampers on the roof top units. Only during the warmest summer weeks, mechanical cooling, two stage for each roof top unit, is needed for any cooling requirements throughout.
In the repair shop, the drive through bays and the new car delivery bay of the building, three separate IAQ controllers are installed to ensure compliance. Utilizing CO sensors, when the CO levels rise above 100 ppm the DDC controller powers open the large overhead doors to a preset level to allow for natural draft in order to gain control of the IAQ levels.
If the CO levels rise to 110 ppm or greater, then a mechanical exhaust fan is also energized to force the ventilation mechanically. As this IAQ control measure is usually only for a short period of time, the thermal mass of the radiant floor helps
reduce the overall amount of heat lost during the ventilation with almost immediate recovery when the overhead door closes again.
LOW TEMP FOR EFFICIENCY
In the mechanical room again, two three-way mixing valves, are dealing with the two water temperature requirements based on the building needs. As noted earlier, through indoor temperature feedback provided from the communicating thermostats, each mixed system will run constantly at the lowest temperature possible to meet the building’s highest heating load at any time. The boilers are staged and rotated based on run-time and modulated to a water temperature that is based on load reset. Load reset sets the boiler target temperature equal to the highest mix temperature requirement, allowing the highest requirement mixing valve to open to 100 per cent and the boilers to condense with cooler return temperatures.
The whole system is remotely accessible for monitoring, comfort control and troubleshooting if required. The system is setup for automated notification to the contractor for maintenance and/or troubleshooting requirements, As many readers can relate, a project such as this often gets reviewed throughout the course of construction due to time and budget constraints. Tri-Mechanical, however, was able to meet all of those needs the first time around. This project even caught the eyes and ears of the president of Toyota in Japan who sent an official letter of acknowledgement to the owners of this dealership.
The building achieved LEED Canada-NC certification in November 2012. This project also won the Ontario General Contractors Association (OGCA) Ontario Builders Award in Category 2, $5 million to $25 million for projects completed between January 2010 and November 30, 2012. Projects are judged on factors including: onsite safety, environmental impact, and owner satisfaction. The award will be presented April 12 during OGCA’s 8th Construction Symposium in Collingwood, ON.
As time goes on, more environmentally friendly and energy efficient systems will be specified and I am excited to be involved in this change in focus.
A video on this project can be found on YouTube.com (http://www.youtube.com/watch?v=w6QyJieCa34).
Mike Miller is a national business development manager with experience in the manufacturing, distribution and contracting sectors of the industry. He can be reached at firstname.lastname@example.org, LinkedIn or @hydronicsmike on twitter.
Firms and individuals involved on this project include:
• Timbro Design Build, General Contractor
• John Morrone, Project Manager
• Richard Rotchill, Site Superintendent
• Paul Bodden, Manufacturer Rep, The Morgan Group
• Mary Schweihat & Tom Keszthelyi, Hallex Engineering
• Grant Peters & Michael Pelton, LEED Consultants, Fluent Group Consulting Engineers