Earth Rangers Revisited

When the Earth Rangers Centre was built in 2004 it caused quite a stir. Photographs of the massive concrete ventilation “earth tubes” being installed – each around 20 metres long, 1 metre in diameter, and buried 2 metres below grade – made for impressive media coverage. They are still the largest earth tubes in North America.

But how did these ungainly features perform? Their purpose is to moderate the temperature of the ventilation air, and according to the Earth Rangers organization they have more than proved their worth in energy savings.

Recently, the 60,000-sq.ft. centre upgraded its building systems and added more features to supplement the energy savings. A ground source heating system, for example, was added below the parking lot.

Today the building uses almost no fossil-based energy for heating and cooling, and it generates a third of its electricity on site. Its energy consumption from off-site sources is only 9 ekWh per square foot.

The Earth Rangers centre is located within the Kortright Centre for Conservation, in Woodbridge on the northwest outskirts of Toronto. Enermodal Engineering were the mechanical engineers and LEED consultants on the original building systems design; MCW Custom Energy Solutions were the mechanical, electrical and energy design consultants for the recent upgrades.

The building was originally designed as a wildlife rehabilitation centre, but today it serves as an education centre to teach children about preserving wildlife and habitat around the world. The long animal wing and aviary are now occupied by “animal ambassadors,” which include large raptors such as bald eagles, and (somewhat out of the Canadian context) lemurs from Madagascar.

The building is an office for 40 Earth Rangers staff and 20 staff from the sustainable technology evaluation program and education group of the Toronto Region Conservation Authority.

Brett Sverkas has been in charge of operating the building for the last year ever since the GSHP system was installed. He was astonished to find out how effective the earth tubes were at tempering the ventilation air. As part of the 2010 upgrades, a new building automation system was added and Sverkas couldn’t believe the readings it was showing.

He explains: “During the commissioning of our ventilation and building automation system (BAS) upgrades, myself and James Raven (project manager for MCW) needed to trend the air flow from intake to discharge. After observing the temperatures via the BAS we were extremely puzzled by some of the values. The outside air temperature was -17°C, the temperature at the exiting side of the earth tubes was +2°C, and the discharge side of the enthalpy wheel was +20°C. At this point we thought that we had a calibration issue with our temperature sensors, so we grabbed the trusty sling psychrometer and observed nearly identical readings to the BAS. That means that we were completely tempering our fresh ventilation air to the desired set point without having to add a mechanical heat source. Needless to say we were both impressed.”

Sverkas estimates that on a day when the outdoor air temperature is -10°C, the tubes conservatively achieve a 10-15 C degree rise in the incoming air. “If the ventilation system is delivering 2500 L/sec, the earth tubes provide approximately 100,000+ btu in an hour,” he says.

The tubes draw 100% fresh air from intakes alongside a detached garage. The intakes are fitted with a standard bird screen, a filter cloth and Merv 8-pleated filters. The incoming air passes through an enthalpy wheel and air handling unit, and then is distributed throughout the building through a displacement ventilation strategy, i.e. the air is fed at low level, cooler than the space temperature, and exhausted at high level from the spaces.

The geothermal field consists of 44 vertical loops buried 120 to 140 metres below the parking lot. This ground source heat pump (GSHP) feeds a radiant heating and cooling system. Heat is delivered or removed via an ethylene-glycol mixture through 22 kilometres of pipe embedded in the concrete floors and ceilings. Since the GSHP was added, the system has displaced almost 150,000 ekWh of gas consumption annually. A high-efficiency gas condensing boiler sits idle for most of the time, gathering dust in the basement.The only time the boiler was used last year was for testing to ensure it was ready if needed.

In summer, Sverkas explains, the ground loop field provides more than enough cooling for occupant comfort without running the heat pump. But the temperature of the fluid coming from the ground is not cold enough to effectively dehumidify the air on hot humid days.

When conditions allow, therefore, Sverkas starts the chiller and runs an overnight “batch scrub.” This procedure allows them to “suck the moisture from the air while reducing the need for reheat,” he explains. Since the scrub occurs during unoccupied times, the system can run at 100% recirculating air, which achieves the dehumifying goal quickly.

Another recent addition is six large photovoltaic arrays, distributed on stands around the parking lot. Each array has 54 x 175W panels, each with its own micro-inverter. The arrays (approximately 4 x 6 metres in area) have a dual axis tracking system that allows them to follow the sun from east to west during the day. (The tracking gear was damaged by freezing this winter and the panels were stuck flat during our visit in early April.) Together with an original 28 kW PV array on the aviary building, the centre’s PV capacity is now 86 kW. A large display monitor in the building lobby shows the performance in real time. Even on an overcast day, the PV system is generating up to 20 kW.

John Pepelnak, sustainability manager of the centre, says the panels will generate up to a third of the centre’s electricity consumption. Thanks to Ontario’s feed-in-tariff program, the centre can sell all the energy generated on-site to the Ontario Power Authority at a rate which is higher than the rate the centre pays to buy power back from the utility.

Solar thermal collectors were part of the original design and are mounted on the reverse of the roof’s north-facing light sheds (dormer windows). The 16 solar collectors heat the domestic water supply, but they sometimes produce surplus energy that can be used to supplement the building heating system. Sverkas explains how this works: a propylene glycol “drainback” tank exchanges absorbed heat between the DHW distribution tank, three preheat tanks and the building heating loop.

The team was able to make this design change thanks to the new sophisticated metering and controls that allow the building team to intensively monitor how the building behaves, down even to the level of individual pumps.

“After studying the performance of the building envelope and the building’s reaction to solar heat gains during the winter months,” says Sverkas, “it has become evident that we should be able to heat the building on sunny days using this system alone, letting the ground source system stand idle. This may seem to be a stretch of the imagination to most engineers, but because of design features such as a radiant concrete structure that is designed to act as a giant thermal battery, the building is able to sustain little space temperature change on average sunny winter days.”

The building also has a “forced cross flow” cooling tower. Usually this would be used to remove the chiller reject heat, but since the chiller is hardly used any more, the tower is mainly used for free cooling. Sverkas also says they have the option to use the cooling tower to reject excess heat from the ground around the GSHP field loop if there is a seasonal
imbalance in the field temperatures.

Within the spacious basement, beside all the gleaming HVAC equipment is a wastewater treatment plant that incorporates both aerobic and anaerobic digestion and ultraviolet disinfection. Two transparent pipes show the before and after product – one filled with dark muddy liquid, and the other clear water. The monitors show that the plant has processed 2,800 litres on this day, but it has a total capacity of 12,000 litres. Ultra low-flow toilets and faucets, rainwater harvesting (there is a green roof), and this on-site greywater treatment plant, mean the building consumes up to 75% less potable water than it otherwise would.

This is an extraordinary building, one that shows that it is possible to operate a building using virtually no carbon-based fuels and very little energy overall. No wonder the young Sverkas seems to be enjoying himself orchestrating and balancing all the different building systems. With this building he is obviously riding the wave to the future. cce