A radiant heating and cooling system is at the forefront of the David Brower Center’s sustainable features.
Buildings don’t get much more sustainable than the David Brower Center in Berkeley, Calif.
The nonprofit facility bills itself as an inspiring home for environmental and social action by combining both offices and program facilities in a 50,000-sq.-ft. layout, promising an invaluable asset for the region and a landmark for those committed to the planet and its inhabitants.
That’s not just rhetoric talking. The Brower Center, which was built on a site that used to be a city-owned parking lot, backs it up when it comes to being a champion of all things green. The facility has earned the U.S. Green Building Council’s Leadership in Energy and Environmental Design Platinum rating — the highest designation available. No other building of its kind exists in green-centric Berkeley, and it’s one of fewer than 10 such buildings in Northern California.
“We have 40 different groups working here,” Brower Center Executive Director Amy Tobin explains. “They are all working on some aspect of environmental or social activism.It ranges from 25-year-old organizations to startups in cubicles.”
And front-and-center among the building’s many sustainable features is an elaborate radiant heating-and-cooling system.
Striving For Optimal Comfort
A total of 31,582 ft. Of radiant tubing (5/8- in. At 12-in. Spacing) is installed in three of the building’s four floors (approximately 10,000 ft. Per floor). The tubing (by Uponor) is located in the ceiling of each particular floor and radiates heat to the floor below it.
“It’s the first building where I’ve seen it in the ceiling,” says Integral Group’s Michele Sagehorn, LEED AP, CEM, and the commissioning engineer on the Brower Center project. “Generally, people think of it in the floor. Here the ventilation system is under-floor and the radiant is in the exposed concrete slab ceiling.”
In this particular radiant system, each zone (each of the three floors contains five zones) has a control valve (by Johnson Controls).If there is a call for heating in a particular space, the control valve opens for that specific zone.
“The water temperature for the radiant heating is quite low,” Sagehorn says. “The highest we ever have it is 90° F.”
If there is an odd day in Berkeley with high temperatures outdoors, the radiant system adjusts accordingly.
“If there was a hot temperature outside, it would go into pre-cool mode,” Sagehorn says. “Condenser water at 60° F will be injected into the slabs and that cools down the building at night. We’d also initiate a nighttime purge and bring outside air into the building to get the thermal mass down for the next day.
“Cooling is totally based on the outside peak air temperature. If it gets to 78° F, it will initiate the pre-cool sequence and switch the radiant loop over from where it may be 75° F to 90° F to the condenser water where it’s 60° F. All of the control valves open until we reach a certain slab set point of 65° F.”
Sagehorn notes that sequence generally stops at 5 a.m. before people enter the building.
“We then let those slabs float throughout the day,” she states. “They are provided no heat. During the pre-cool sequence, we don’t ever let the slabs get lower than 65° F. The ventilation air is not intended to cool the space, but to help with comfort. It will take that whole day to get that slab up high again with the thermal mass.”
Finding What Works
Equity Community Builders’ Suzanne Brown, the development manager and project manager for the design and construction of the Brower Center, knows a thing or two about how the system works.She’s a tenant in the building and also oversees the property’s management team.
“I live all of this first-hand here,” she says. “We don’t go into cooling mode very often. It’s only happened twice in a year-and-a-half since it’s been open. It doesn’t get all that hot in the Bay Area, especially here in Berkeley. The radiant is pretty substantial here. The building gets high marks for thermal comfort and air quality.”
The system did have some minor growing pains when the building opened.
“There weren’t too many issues in May,” Brown says. “It got pretty foggy and cold here in August. We don’t have the same summer as everywhere else. It was hot in June and then it started to get cold in July and August. People complained about it being cold, so we looked at the slab temperature. The engineers came in with radar guns and shot the temperature of the slab above the windows and concrete walls. It was maybe 70° F or 72° F. Six or eight feet below the ceiling where people sit, it was 62° F. We raised the temperature and left it like that 24 hours a day, seven days a week.
“Due to the large thermal mass of the slabs, it used to take into the afternoon to heat up the building. We figured it out and changed the set point and now the building feels great. It’s more energy-efficient by drawing on the gas that heats the water in the boilers in spurts instead of having a big draw and turning it off.”
Sagehorn adds the controls contractor initiated a night setback for the zones (slabs), which meant at night the slabs were trying to achieve 65° F.
“This would take all night to lower the mass of the building and when people walked into the building in the morning it was cold,” she explains. “We would switch over to heating, but it would take all day to get back up to temperature, resulting in a comfort problem.To fix this, we essentially eliminated the night setback set point and kept the same set point day and night. What we found was it took less energy to leave the slabs at a common set point all the time vs. a night setback where the system was essentially fighting itself. A night setback set point is very common in traditional buildings as a method to save energy. However, that same principle did not apply to radiant heating or this building.It was a different strategy.”
Sagehorn agrees patience and some trialand- error were needed in getting the building to produce the desired comfort results.
“It wasn’t difficult, but it required a year of seeing how the building responded and finding that comfort level,” she says. “The comfort level is a combination of the slab and the air temperature. In a typical office building, 74° F or 75° F might be comfortable. Here, we see people comfortable at 70° F and 72° F. It will feel comfortable at a lower set point because of the thermal mass of the building. We’re tempering the ventilation air (100% outside air), which is a much smaller quantity of air than a traditional air heating system.”
Employing this particular method of heating and cooling has yielded major returns in terms of the building’s energy efficiency.
“Using water to heat is more efficient than air,” Sagehorn says. “Tempering the ventilation air means only heating it to 70° F to 74°F. This only requires hot water between 90° F and 120° F. Most air systems require 180° F for hot water to heat the air, which means we are saving a lot of energy. We’ve got two small condensing boilers (by HydroTherm) that are super-efficient because the return water is at a lower temperature. We’re getting peak efficiency out of these boilers.”
Tenant reviews of the overall effectiveness of the system have been stellar.
“People says it’s so much better than having air blowing on them,” Sagehorn states.
The Brower Center does not employ a traditional chiller, which again keeps the energy pocketbook from bleeding cash.
“The cooling tower (by Marley) is essentially free cooling using evaporation,” Sagehorn says. “The cooling tower and fan is a lot Less energy-intensive than a chiller would ever be. If you don’t need the temperature to be 55° F and you’re not cooling the building with an air handler and have higher water temperatures, you can get away with just a cooling tower because of that higher temperature and the tempering of the air as opposed to using the air to cool the space.”
A plenum sits under the raised floors on each level allowing the supply ventilation air to disperse. An under-floor switch gives the user control of opening and closing the defuser.
Taking Care Of The Ground Floor
With the tubing being in the ceiling, the ground floor of the center, which houses numerous public spaces including an intimate theater, does not have the benefit of the radiant system. This creates somewhat of a domino effect on the upper floors.
“The third and fourth floors are generally a little warmer than the second,” Sagehorn notes. “The second floor is at a slightly higher set point because the first floor has no radiant.”
Thus, a few water-source heat pumps (by Florida Heat Pumps) are located on the first floor.
“In general, the building doesn’t react quickly. However, certain areas, such as the theater, need to have that capability,” Sagehorn says. “Those types of areas located on the first floor are served by heat pumps that are supplied with condenser water. We pump the water to the heat pumps during the day and the loop heat exchanger is tied to the cooling tower. When the condenser water gets over the set point, the cooling tower will turn on.”
And That’s Not All
Efficiency toilets (Caroma), water-saving lav faucets (Sloan), water fountains (Haws), kitchen faucets (Delta) and mop faucets (Fiat) make the building 40% more water-efficient than a typical office building. Domestic water is heated with a Laars water heater.
A rainwater catchment system collects water from the building’s roof and from the attached housing development and runs it into a 5,600-gallon cistern (by Snyder) in the basement. That water is then used for toilet flushing and irrigation.
The building employs SunPower photovoltaic panels, which double as a sunshade device. The 100% daylighting of all office areas, CO2 sensors that call for extra fresh air if required and high-efficiency lighting help contribute to the building’s superior carbon footprint.
The Brower Center is adjacent to a retail space and Oxford Plaza, a residential project offering 97 green and affordable apartments for low-income families and individuals.
Oxford Plaza has in-slab perimeter radiant heating, which absorbs heat from the space as needed. Due to good insulation and window selection, only a 4-foot band of radiant tubing, located near exterior walls, is needed. A high-efficiency condensing boiler operates at a lower supply water temperature with higher efficiency, using pumps with variable-speed drives.
The residential development uses a solar hot water panel collection system comprised of 16 Heliodyne Gobi 410 collector panels, which provide 30% of peak hot water demand. The collectors return heated water to the central storage tank, and, during most periods, the solar hot water system provides a boost to the domestic hot water system boiler.That storage tank is then used by the radiant in-slab system during the heating season.
See It For Yourself
The Brower Center features an Internetbased dashboard that shows the building’s water, electrical and solar usage.
“We received a grant to put in some additional power meters to measure how Much energy all parts of the HVAC system are using and we’re looking at how we measure the PV on the roof,” Brown says.“Adding in a couple of other meters and splitting systems up gives us a more accurate reflection on energy usage.”
Sagehorn did an energy analysis on the building using utility bills from June 2009 Through May 2010. The site Energy Use Intensity for the time period was 47 kbtu/sq. Ft. Per year without PV energy and 38 kbtu/sq. Ft.Per year with PV.
For Brown, being in the building on a continual basis has further aided in the study and fine-tuning of the structure’s systems.
“It helps to have the project manager in the building living through the problems and making sure they get corrected,” Brown notes. “A lot of times, buildings are turned over to the property manager and the people that built it are quickly down the road and not looking back. (Integral Managing Director) Peter Rumsey and Michele have worked so closely with us in terms of fine-tuning the operation of the building’s mechanical systems. If anything goes wrong they will help our building engineer to troubleshoot. Client care by the design engineer after building occupancy has really helped the owner learn how to use this high-performance building. They have really shepherded us though the process of how to operate the building efficiently.”
Tobin says the building has already more than lived up to its billing.
“The idea was to make it be sort of a laboratory for green design, to study which innovations work,” she says. “And it’s working.This place was designed to be an inspiring destination. We’re fulfilling that promise and taking inspiration from our namesake, David Brower, who is considered by many to be the father of the modern environmental movement.And now we’ve set the standard here with the greenest building around.”