September 29, 2017
Heat pumps have been the go-to pool heating option in Florida and Quebec for years. In fact, the trend is spreading into Ontario, as well. An increasing number of pool owners are opting for heat pumps over propane, natural gas, oil, and electric heaters for a number of reasons, including operating costs, environmental impact, and overall efficiency.
As summer ends, some pool owners who were attracted to the low price of a fossil-fuel heater may look back on their heating bills between spring and summer and think about ways they could have saved money in their effort to extend the swimming season. Those homeowners who chose to purchase a heat pump are likely not experiencing any buyers’ remorse, as their monthly heating bills may have cost them as little as one fifth as much as a traditional pool heater.
A heat pump operates in reverse fashion to an air conditioner by pumping warm, outside air straight into the pool. The electricity the unit uses does not heat the water directly; it powers a compressor and a fan, which transfers heat energy from the ambient air into the pool water.
The entire process is controlled by a simple electronic display, whereby the temperature of the pool can be set anywhere between 18 and 35 C (65 and 95 F).
A typical electric, propane, or natural gas heater is considered ‘efficient’ when more than 80 per cent of the kilowatts (kW) or British thermal units (Btus) of energy are transferred into heat energy.
A pool heater’s coefficient of performance (COP) measures the relationship between the amount of heat it generates and the energy it uses to do so. A COP of seven means that for every dollar of electricity used, the homeowner gets the equivalent of seven dollars in heat energy for their pool. This is achieved by using a process based on thermodynamics, which produces some of the most efficient heating energy on the market. For the sake of comparison, and perhaps even over-simplifying the differences, a COP of seven is akin to 700 per cent efficiency.
For most pool owners, comparing 95 per cent to 700 per cent should be an easy choice, and a good reason to learn a little more about thermodynamics. A simple way to explain a heat pump’s “reverse air conditioning” operation is they work using the principle that gases heat up when compressed and cool down when released. Heat energy is transferred from the heated compressed gas into the pool water as it flows through the heat pump. Since electricity is used to power the compressor and fan, rather than a traditional heating element, up to seven times less energy is used to attain the same pool heating result.
More advanced heat pumps also offer smart ventilation management that optimizes the pool heater’s energy performance based on outdoor temperature.
Heat pumps can work in temperatures as low as 5 C (41 F); the hotter it is outside, the better, since heat pumps transfer ambient air heat energy into the pool water.
First, it is important to get a unit that is the right size for the pool. A general rule of thumb is to install a minimum one to two Btus of capacity for every litre of water in the pool. When possible, it is recommended to select a unit that can deliver beyond the homeowner’s minimum requirements.
Heat pumps with higher capacities offer many advantages: they operate less, they get the pool to a desirable temperature faster, and they will be able to maintain the target temperature longer into the season.
When looking at the heater costs table (Figure 1), it is easy to see the huge difference in yearly operating costs depending on the type of unit that is installed. There are also differences in local energy costs for electricity, propane, and natural gas, as well as variances in personal preferences for desired temperatures and, of course, pool shapes and sizes vary, too.
However, all things considered, it is only a matter of time before the lower monthly energy bills cover the increased upfront cost of a heat pump. In most cases, this takes between two and five years.
Figure 1: Pool heater cost comparison
|Installation||Heat Pump||Natural Gas Heater||Propane Heater|
|Output||120,000 Btu/hour||232,000 Btu/hour||198,000 Btu/hour|
|Efficiency||Heat pump COP6||82 per cent||80 per cent|
|Costs per:||kW $0.15||Million Btu $13.40||Litre of propane $0.60|
|Initial cost to heat up pool||$24.22||$54.34||$100.88|
|Cost per day to keep water at desired temperature||$4.54||$10.19||$18.92|
|Runtime per day (hours)||5||3||3|
|Cost for season||$569||$1,280||$2,371|
|Cost difference per season||—||$711||$1,802|
*These are approximate figures based on calculations for a 75,000-L (19,813-gal) pool, heating in average seasonal temperatures in Toronto between June to August.
Making an environmentally conscious choice does not solely rely on pool owners. For instance, heat pumps do not burn propane, natural gas, or oil, keeping greenhouse gases out of the air, which is a preference supported by many energy suppliers. Another reason why a pool owner may choose an electric-powered heat pump over a gas-fired unit is 90 per cent of the electricity in Ontario is generated through non-carbon sources (60 per cent nuclear, 24 per cent hydro, and six per cent wind). An electric heat pump that turns every kilowatt of power it uses into seven kilowatts of heat is, therefore, extremely efficient and one of the most environmentally conscious choices a pool owner can make.
The most cost-effective heat pumps can help to optimize the entire pool system when combined with other high-efficiency equipment, such as a variable-speed pump (VSP). The combination of these systems makes sense because heat pumps operate more efficiently when there is a higher rate of flow through the system; however, operating the pool in this manner 24-7 is counterproductive, as it can also waste energy. Therefore, to improve efficiency, a VSP allows the flow rate to be increased when the system is actively heating and, when the desired temperature is reached, the flow rate is reduced, thus increasing energy savings.
By decreasing the amount of time the pump is running at high flow, the system emits less overall ambient noise, which is another advantage of combining these technologies. This is ideal for neighbourhoods where homes are located close together, or where municipal noise bylaws are stricter. In general, noise restriction is an increasingly important issue throughout North America and heat pump manufacturers invest significant resources in research and development to address it. Consequently, the best units boast an operating noise level of only 50 to 55 decibels.
That said, it should come as no surprise to the homeowner that leading heat pump manufacturers and installers will recommend combining a VSP with any new unit to maximize efficiency. However, something to look out for when pricing these two complementary components is an assurance they can work together properly. Some manufacturers may even offer unique, simple operating modes that enable the pool heater to communicate with a VSP.
When they work together properly, the pump speed adjusts automatically to the needs of the heater (i.e. a higher water flow when in heating mode). The VSP also lowers the rate of flow and, of course, reduces noise, when the pool heater no longer needs to operate.
Pool owners looking for even greater efficiencies can add a water-cooled motor. It contributes to heating the pool water at no additional cost, because the motor recovers and returns the heat it generates to the pool.
|How to specify the right heat pump|
|As heat pumps become increasingly popular in the North American aquatics market, with no shortage of options, the following is a quick checklist to consider when selecting the right heat pump for the job.
Unlike natural gas or propane systems, there is no need to run a gas line through the backyard when using a heat pump. There is no need to install a large propane tank, either. Some pool owners might confuse heat pumps with geothermal heating; however, heat pumps are self-contained and only require simple connections to the circulation system. Geothermal heating options, on the other hand, often require a fair amount of excavation or drilling.
A heat pump simply needs two connections: one for electricity (typically a 220V power source) and one to the pool’s VSP, usually with a dry connect (if applicable). It connects to the pool water line with a simple plumbing job; a bypass with quick-connect is recommended to simplify tasks such as cleaning, maintenance, and winterization.
Since a heat pump uses heat from the ambient air, the unit needs to be outside in an open area. If there is an area around the pool that gets lots of sun, or is particularly hot in the summer, these could be great spots for installation to maximize efficiency. An interesting side effect is the area around the heat pump will actually get cooler when it is operating.
The heat pump should be installed as far away as possible from walls and fences with a clearance of at least 300 mm (12 in.). Better air circulation around the heat pump will improve its efficiency by increasing the ambient warm air available that can be transferred to the pool.
When it is time to close the pool for the season, protecting and winterizing a heat pump is simple. The first step is to turn off the electrical breaker. Then, unplug the bypass lines and tilt the unit to ensure it drains properly. As with any pool equipment, removing as much water as possible from the pipes is critical in climates with sub-zero temperatures. Finally, the water intake and outlet should be covered or plugged to make sure dirt, snow, water, or critters do not get inside the unit over the course of the winter.
Thanks to the many benefits heat pumps offer, it is no surprise that an increasing number of homeowners are considering these systems to heat their pool. Retailers can easily sell heat pumps based on their efficiencies and performance, which can significantly reduce a pool owner’s water heating costs (up to 75 per cent in some instances).
Further, purchasing a heat pump gives those homeowners who try to make conscientious ‘green’ choices something to be proud of when it comes to the operation of their pool. In a society that is moving away from carbon-based energy sources, heat pumps offer an energy-efficient option.
Geoffrey Pelsise is vice-president of research and development at Nirvana Heat Pumps Inc., a manufacturer of heat pump equipment in Grand-Mère, Que. Pelsise endeavors to develop energy-efficient technologies for swimming pools. He has been with the company for seven years and can be reached via e-mail at email@example.com.
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