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Achieving ‘Net-Zero’ Energy

Johnson Controls installs a unique HVAC system at IDeAs headquarters in San Jose, California

| | Mar 15, 2010 | 12:40 pm
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Johnson Controls installs a unique HVAC system at IDeAs headquarters in San Jose, California

Johnson Controls’ Davide Kaneda, Jeff Crenshaw and John Coleman

Johnson Controls’ Davide Kaneda, Jeff Crenshaw and John Coleman

Johnson Controls designed and installed a unique heat pump-based HVAC and control system at the new headquarters of Integrated Design Associates (IDeAs) Inc, which is a testament to the latter’s commitment to help architects design the best and most energy-efficient buildings. The headquarters is the first commercial office building in the US designed to meet a netzero energy/net-zero carbon emissions goal, or Z2.

The goal was to transform a 1960s-era, windowless concrete bank into a highly efficient and comfortable building using a fullcomplement of sustainable design techniques and technologies. (The energy efficiency for the HVAC system and building envelope is estimated to be 40% below 2005 California Title 24 energy requirements.)

The result is an office building that uses renewable energy from photovoltaics to meet 100% of its energy requirements, burns no fossil fuels and produces no net greenhouse gas emissions.

DESIGN INC

The design incorporates a geothermal heat pump, which takes advantage of the fact that the temperature below ground remains constant all year round – about 10ºC in this case. Water flows through pipes laid under an open landscape area and passes into the building, where a heat exchanger collects heat from the water in winter and uses the water’s cooling-effect during summer. A radiant floor system with cross-linked counter-flow tubing uses the water to convey heating and cooling to the space.

The system uses less energy to provide the same level of comfort as traditional systems, owing to temperature variance between the occupant and the floor itself. Radiant systems typically can use higher water temperatures to provide effective cooling, and lower water temperatures to provide effective heating. This means that the equipment operates at higher-efficiency levels.

“Since the system has been operating it has already provided a very cool and comfortable environment during some very hot weather,” says David Kaneda, the principal of IDeAs. “It is a very efficient system that will help us meet our net-zero-energy target.”

Kaneda had thought of bringing this concept to life when his company bought a 7,200-square-foot former bank branch to house its new headquarters. “We felt we should walk the talk, not just talk,” he remarks. A consultancy providing electrical engineering and lighting design services, IDeAs has clients involved in projects like educational and medical facilities, office and retail spaces and restaurants and apartments.

SUSTAINABLE TECHNIQUES

A Johnson Controls Metasys building management system accurately controls the flow rates and slab temperature to provide the maximum performance using the least amount of energy. Pump speeds are kept at their lowest demand by using power inverter technology that responds to actual demand. Floor condensation is monitored and dehumidification provided, if needed, with an air-handling system that uses water from the geothermal system.

PEX piping and valves are visible inside wall cabinets, making it easier for the host to explain to visitors how the system works

PEX piping and valves are visible inside wall cabinets, making it easier for the host to explain to visitors how the system works

A building integrated photovoltaic system is the facility’s energy source. The panels in this system are part of the single-ply membrane roof installed on the facility. The electrical system is tied into the grid, so it will draw power at night when there is no sunlight, and deliver power back to the grid when more energy is generated than is being used during the day. The result is designed to be ‘net zero’ in overall energy use.

To reduce the amount of energy used for lighting, Kaneda’s team added windows and cut skylights into the roof to take advantage of available daylight. High-efficiency windows let light through but block infrared and ultraviolet light, keeping the office cool. An overhang shades south facing windows and those facing east incorporate electrochromic window glazing, which is controlled by a sensor that darkens the windows when the sun hits them directly.

Low-energy fluorescent bulbs used throughout the building are controlled by occupancy sensors, or these have dimming ballasts to reduce energy consumption. Light sensors turn off select fixtures when sufficient daylight is available. Energy conservation extends to computers and office equipment as well. LCD flatscreens take the place of traditional monitors, which use 50% more power, while laptops replace desktop computers where possible.

The design team integrated office equipment with the building security system, automatically shutting the equipment down when the security system is armed – and restoring power when the system is disarmed.

“All of the technologies we are using are readily available,” Kaneda says. “Some of them are more expensive from a first-cost standpoint, but the reduction in energy use will pay longterm dividends. And it’s the right thing to do from the standpoint of reducing our impact on the environment.”

MORE EFFICIENT, LESS COSTS

The innovative HVAC systems in the IDeAs headquarters are a key contributor to minimising the building’s energy consumption and maximising performance and indoor air quality while keeping construction costs comparable to more traditional designs.

Photovoltaic solar panels are integral to a single-ply membrane roof

Photovoltaic solar panels are integral to a single-ply membrane roof

The Radiant Floor System. A topping slab, poured over the existing slab, contains a crosslinked counter flow polyethylene (PEX) radiant tubing system for both heating and cooling. Using water to convey heating and cooling to a space in a radiant system uses less energy to provide the same amount of conditioning compared to a forced air system, owing to the radiant-effect created by the floor temperature variance between the occupant and the floor itself.

Also, radiant floor systems typically use higher water temperatures for cooling and lower water temperatures for heating compared to traditional systems, allowing the equipment providing the water to operate more efficiently.

High-pumping efficiencies are gained by the design of a low pressure drop piping system, coupled with open-ported, ball-type control valves. The Metasys building management system accurately controls the floor cooling/heating flow rates and temperature, to provide the maximum performance for the lowest pumping power and most efficient water temperatures.

Pump speeds are kept at their lowest demand speed using power inverter technology based on actual demand. Floor condensation is prevented by the system, which compares the floor temperature to the room air-dew point temperature. Dehumidification is provided, if needed, by the air handler using chilled water and concurrent condenser water for temperature control via a pair of dual coils in the air handler.

The Heat Pump. An electric, water-source heat pump produces both chilled water and hot water to maintain the net-zero energy and zero carbon emission philosophy of the IDeAs building. The chilled or hot water is provided both to the radiant slab and the dedicated outside air handler to condition the space.

The heat pump has a cooling energy-efficiency ratio (EER) rating over 19. The open-landscape area behind the building was used as a ground source heat sink for energy absorption and rejection, and as storage for the heat pump system. The earth under this area is trenched with a field of PEX piping six feet and four feet deep to provide an energy storage field.

System efficiencies are increased by providing a relatively steady temperature heat sink for the heat pump system, rather than using outside air to absorb and reject heat, which would mean that temperatures would vary more widely. The thermal storage capacity of the earth also allows for high-efficiency between heating and cooling modes of operation, which alternate from morning to afternoon.

An illustration of the HV AC and control systems at IDeAs headquarters

An illustration of the HV AC and control systems at IDeAs headquarters

A dedicated outside air handler with high performance filtration and constant temperature control provide high performance ventilation for the building. Operable windows and doors installed throughout the building allow the occupants to tailor their comfort levels by tuning the openings. However, when outside air temperatures are too cold or too hot and the windows or doors are not utilised, the dedicated outside air handler provides the required ventilation in the building. Chilled or hot water supplied by the heat pump to the air handler will condition the air delivered to the space.


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