Goodbye to gas in aquatic centres

BRITISH COLUMBIA OPENS UP NEW PATHS IN ENERGY MANAGEMENT

Author Taio Waldhaus (P. Eng, CPHD), Principal, AME Group

Many municipalities in British Columbia, Canada have signed up to the Paris Accord, declared a climate emergency and made commitments to eliminate carbon emissions from new buildings in the following decade(s). As aquatic centres are among the highest energy-consuming of municipal facilities, efforts have been made in the design and construction of recent aquatic centres to sever the connection to gas infrastructure, resulting in all-electric facilities. Taio Waldhaus takes a look at energy-efficient mechanical systems in aquatic facilities.

British Columbia’s electricity grid is over 90% carbon-free, resulting in very low emissions associated with the electrified facilities. On-site electricity production, such as photovoltaics, to offset the remaining emissions from the grid, results in net-zero carbon emissions to be achieved in new facilities as defined by the Canadian Green Building Council’s standards.

Operating costs typically far outweigh the capital construction costs for aquatic centres over their useful life. Gas is much lower in cost than hydro per unit of energy delivered when it comes to heating a building in British Columbia. This results in the need to substantially reduce energy consumption associated with these facilities when electrifying them. The following passage describes mechanical system design strategies that successfully minimize the energy consumption of heating and process equipment in the march to remove our dependency on gas in aquatic centres.

Synergy in energy transfer The primary function of an aquatic centre is to maintain heated pools and hot shower water for bathers. Warm bodies of water constantly release water into the natatorium air due to evaporation. In order to maintain comfort on the pool deck and protect the building’s envelope from damage due to condensation, the moisture must be removed from the air through dehumidification. The processes associated with these building features create synergy in energy transfer that, when addressed holistically, can result in substantial energy reduction.

Heat pumps are frequently used in buildings to produce heat. They are ideal as they require substantially less energy input than boilers. This is due to the fact that they move heat, rather than generate it as boilers do. This is possible due to the refrigeration cycle. Hot compressed gaseous refrigerant absorbs heat from sources such as the ground (geothermal) or the outside air (aerothermal) that can be transferred while it condenses to building uses such as heating, domestic hot water and pool water.

How to increase the COP Heat pump efficiency is expressed by its Coefficient of Performance (COP). It is a measure of the heat output divided by the electrical energy input. A typical geothermal heat pump operates at a COP of 3, transferring three units of energy from

Heat recovery chillers

Rendering: AME Group

The təməsewtxʷ Aquatic and Community Centre is currently under construction in New Westminster, British Columbia and will be the first net-zero carbon aquatic centre in Canada as certified by the Canadian Green Building Council. Designed by HCMA Architecture and the AME Consulting Group, it utilizes the technologies described herein and is modelled to produce just 6 kgCO2/y/m² before photovoltaics offset that value to zero.

the source (ground or air) to the load (building) with every one unit of electrical energy input. This is three times the amount of energy output that a boiler produces for the same energy input. Heat pumps can also operate in reverse to provide cooling by transferring heat from a source such as the natatorium air to the sink such as a geothermal field or outside air.

Magic happens when a heat pump is used to provide heating and cooling at the same time. The COP doubles. So, if a heat pump is simultaneously dehumidifying the natatorium air, while heating the pool at the same time, it can operate with COPs as high as 6 or 7. This translates into six units of energy provided to the building for every one unit of electrical energy consumed by the compressors – six times that produced by an electric boiler, which operates with a COP of 1. In order to substantially reduce an electrified aquatic centre’s energy consumption, as much heat as possible should be provided by a water-to-water heat pump doing simultaneous heating and cooling. Whenever there is a cooling requirement in the building, the heat pump recovers heat from that process and transfers it to the heating system. Only when heat requirements exceed what can be produced by the heat pump, aerothermal heat pumps and/ or electric boilers can be utilized to produce the remaining required heat.

Taking advantage of simultaneous heating and cooling Modern aquatic facility operators require mechanical cooling and dehumidification in their natatoriums even in the summer months. In addition, many provide amenity spaces in the facility such as fitness spaces and gymnasiums. These spaces require cooling even in winter months due to the heat generated by active bodies. The result is very good for a building’s energy system as it allows substantial and prolonged periods of time when advantage can be taken of simultaneous heating and cooling. In my experience, a typical aquatic centre can utilize a water-to-water heat pump for on average one third of its peak heating needs.

In order to maximize the use of the water-to-water heat pump plant, the building’s air systems can be designed with both mechanical and passive exhaust-air heat recovery. Even with air-to-air heat recovery such as heat recovery ventilators, warm air is still exhausted from the building to make space for fresh air. By utilizing heat recovery coils in the exhaust air streams, additional heat can be transferred from that exhaust air to the building through the heat pump plant. This is particularly advantageous in the natatorium where expelled air is quite warm and moist, containing ample energy. With both forms of heat recovery, control systems can switch modes depending on the heat profile of the building, maximizing heat production by the heat pump plant.

This is not the end of the energy reduction story in aquatic centres. There are many areas where incremental energy reduction can add up to substantial energy savings for the building. Gravity filtration has proven to reduce pool filtration system pumping energy by up to 60%. Sanitary heat recovery systems can capture energy from spent shower water that would otherwise go down the drain. Utilizing heat wheels on natatorium dehumidifiers have been proven to reduce that process’s energy costs by CAD 60,000 per year according to recent building energy models conducted on the təməsewtxʷ Aquatic and Community Centre. The key is to prevent any energy from exiting the building if it can be re-used within.