26/11/2020 by Gary D | 01 May, 2018 0 Comments
Pool Heating: A Guide
Selecting a Heater for Your Pool or Spa
We have had an extended summer this year. What do they call it, “Indian Summer”? Well, it’s going to get cold soon, I guess. We are always receiving a large number of inquiries from domestic and commercial pool owners on the options available to heat their pool. In this blog, I hope to impart some relevant information about heater options for your pool or spa.
I don’t want to get into cost analysis in this blog. It will be more about the types of heaters and their pros and cons. But, by all means, contact us or drop by at Billabong Pool Service & Supply for more information.
For 40 years, we have been specifying and fitting heaters to a diverse range of pools and spas. We would be pleased to discuss your heating needs and provide an obligation free quote.
It is apparent to us that there is a lack of balanced information available to allow potential purchasers to understand the basics of pool heating. In many cases, heater selection is being made without buyers being correctly informed on the important issues of performance expectation and operating costs.
Capital outlay appears to be the main motivating factor for selection, whereas ongoing energy costs and plant maintenance should be the major area of review. Our hope is that the information contained in this blog will be of assistance to those considering a heater purchase.
The most cost-efficient way to heat a pool is with an electric heat pump.
The second is with gas, providing gas purchase price is competitive.
The third is with electric resistance element. On certain tariffs, resistance can be competitive with gas.
We do not consider solar an option in this guideline, as it is not a standalone system that can offer acceptable commercial swimming water temperature during winter. Solar is sometimes marketed in conjunction with gas or electric boost. With these systems, the following points must be considered:
- The boost system must be sized to be a standalone heater when there is no solar input.
- In winter operation, the solar system contributes little to satisfy the total heat load. To input any available solar gain, there needs to be a control system in place to effect change over of energy sources.
- For homeowners, solar should be considered to extend the swimming season in spring and autumn.
- If a solar installation is being considered, the purchaser should request that the installer provide a written projection of the expected pool water temperature for each month.
These are also a consideration when talking about pool heating by contributing to heat retention. The subject of pool covers deserves its own blog.
The industry-standard target water temperature for comfortable swimming in commercial pools is 28.0 degrees C. Spas are normally operated at 38.0 degrees C.
If you have installed a heater that achieves anything less than the target temperature, the heater is incorrectly sized for the installation, and the project is seriously flawed.
Q. At what time of the day should the target temperature be achieved and what is the pool temperature at the start of swimming days?
A. It is not a satisfactory situation to have a heating system that, for instance, achieves target temperature at midday.
Available Heating Systems
Electric Heat Pump:
Available in single and three phase supply and is basically a refrigeration unit working in reverse.
By use of refrigerant cycle, energy efficiencies are high, with averages of (1) unit of energy input to the heater, resulting in (4.5) units input to the pool water.
The input to output ratio is referred to as “The coefficient of performance” (COP).
Heat pumps are usually rated at Kilowatts / hour output. (KW)
An enclosure houses a compressor, evaporator coil, copper nickel or titanium heat exchanger and fans. The fans draw ambient air over the evaporator coil and heat from the air is transferred to the cold refrigerant in the coil. The resultant cold air is exhausted by the fan.
The now warmer refrigerant flows to the compressor where it is compressed and heated then passes to the heat exchanger where heat is transferred to the pool water flowing through the exchanger.
The now cooler refrigerant passes to an expansion valve, the pressure is greatly reduced, which in turn chills the refrigerant to a cold gas. The refrigerant flows into the evaporator coil and the heat collection process again commences.
Heat pumps can be indoor or outdoor located. If located indoors, exhaust air must be ducted to the atmosphere or away from the evaporator coils in the case of large-area installations such as car parks.
Because the unit employs refrigeration technology, there is high energy efficiency with resultant low operating costs in comparison to other forms of heating. Both ambient air and pool water temperature determine the efficiency of the unit, and hence the heat output is not linear as is virtually so with other forms of heating. Warmer ambient air allows for increased output.
For the purposes of model comparison, the Heat Pump Association has set an arbitrary figure of rating heat pump outputs. They are:
- Air on to evaporator temperature shall be 15.0 degrees C with dry bulb reading.
- Water entering the heat exchanger shall be at 27.0 degrees C.
If you compare quoted model outputs, this is the figure to look for. Energy outputs stated at other air temperatures or wet bulb are not comparable.
As a rule of thumb, standard build heat pumps operate with a noise level of around 68dba @ 3.0 metres. This noise is generated by the compressor and fans.
You should be aware of the following
In the near future, all new air conditioning and heat pump installations will be checked for conforming to local authority noise guidelines before commissioning.
Noise complaints must be investigated by local authorities, and owners of noisy machinery can be directed to comply with regulation or shut down. Such complaints usually come from neighbours, holiday guests or permanent tenants and can arise at any time in the working life of the heater. To attenuate an existing installation can be expensive and, in some cases, most difficult to achieve.
At the point of ordering, there are a number of options available to specify a heater with an operating noise level of less than 68 dba.
If considering a heat pump purchase, close attention must be given to the potential for a noise complaint, particularly if the property:
- Has a limited choice of locations for siting the unit
- Is located in a quiet neighbourhood away from traffic noise
- Building is positioned around the pool area with rooms above
All of the above factors will determine whether the site is suited to a heat pump. They also set the available operating hours to achieve the target temperature and, consequently, the energy input needed to heat the pool in the available time frame.
By far the most economical form of pool heating.
- Price-stable source of energy.
- Clean on-site operation.
- No tanks to refill.
- Highest capital cost of any heating system
- Operating noise level
- Physical size
- More mechanical components than other types of heaters
Correctly sized and located heat pumps are excellent pool heaters even though capital outlay is high, costing can usually be amortised over two to four years by virtue of the available high energy efficiencies.
Gas Boiler System (LPG):
They can be outdoor located or indoor with appropriate fluing. In certain indoor installations, mechanical ventilating may be needed.
Generally, pool heater boiler efficiencies are around 50-80%. This means that (1) unit of energy put into the heater results in (0.5-0.8) units being input to the pool water.
Gas heaters are rated in megajoule/hour input (fuel energy consumption) and usually in kW output.
These are a simple heater with a set of gas burners, surrounded by heat-insulating material. Heat from the burners is directed up over a finned cupro nickel heat exchanger through which passes the pool water. The components are typically contained in a galvanised steel Colourbond enclosure, which also houses the necessary thermostat control systems and displays. Pool water flow across the heat exchanger is automatically modulated at the heater inlet header.
- Relatively compact. Easy to site in tight locations
- The physical size of the heater does not appreciably alter for the model range across the energy output spectrum.
- Silent in operation
- Relatively low capital outlay
- Can be economically upsized in specification to offer higher outputs
- Mechanically simple
- Less stable price of energy (Consistent with world oil pricing)
- High operating costs as a product of existing energy pricing and heater efficiency
- Small quantities of carbon monoxide exhaust
- Hot to touch cabinet. Has shorter working life than heat pump and resistance heaters, especially in outdoor locations
- Requirement for bottle or tank placement on-site and ongoing refill requirement
- Still the most used form of commercial pool heating, particularly up to 120.0 kW. Widely used on spas where a quick temperature recovery rate is of benefit.
- Most popular in geographical areas with access to natural gas.
Gas Heat Exchange System (LPG)
These are relatively new to the market in Queensland but have been fitted to many commercial properties in Victoria and New South Wales for a few years now. There are a number of units installed in commercial properties on the Sunshine Coast.
These offer efficiencies of around 100%. Installed systems are proving to offer considerable savings on gas consumption over conventional pool LPG heating. Indications are that the running costs are approximately 40% less than those of conventional pool heating. This means the heat exchange systems are better placed to compete with Heat pumps for low operating costs (depending on the LPG price).
This system works via a closed circuit of water being heated by a Bosch 32 ‘commercial’ instantaneous water heater and being circulated through a heat exchanger. This is then plumbed in line to circulate the pool water through the heater, which transfers the heat from this circuit to the pool water.
More economical form of pool heating than standard LPG boiler
- Small footprint compared to heat pumps. Physical size allows fitting in tight locations
- Silent in operation
- Mechanically simple
- High capital cost
- Less stable price of energy (Consistent with world oil pricing)
- Very small amounts of carbon monoxide exhaust
- Requirement for bottle or tank placement on-site and ongoing refill requirement.
Electric Resistance Heating:
Available in single or three phase power. Units over 6.0 kW are usually three phase.
Resistance heaters have a theoretical efficiency of 100 %. This equates to (1) unit of energy put into the heater results in (1) unit of energy put into the pool water.
Resistance heaters are usually rated in Kilowatt output. (KW)
A simple heater consisting of a plastic or stainless-steel cylinder with a series of incoloy sheath elements immersed in the pool water that flows through the cylinder. Heat exchange takes place between the element surface and the pool water.
Only suitable for use within a weatherproof enclosure.
- Very compact physical size for energy output
- Silent operation
- Clean on-site operation
- Price stable energy source
- No tanks to refill
- Expensive to operate on standard tariffs when compared to other forms of heating.
- Elements are susceptible to attack from aggressive pool water and salt.
- Popular and economical form of single-phase heating for installations calling for up to 6.0 kW capacity.
- Also popular for larger pool and spa heating because of small physical size combined with energy output.
- Suits installations where a gas heater cannot be flued because of building restrictions or gas storage is unwanted / difficult.
- Fits in where there is a preference for electricity, but a heat pump cannot be used.
Heater corrosion in any aquatic location and especially on the Sunshine Coast is a matter of some concern.
You should expect an operational life of 10 years plus from a heat pump.
To achieve this, we insist that the heater enclosure be constructed of plastic, stainless steel or aluminium. It is uneconomic to replace an enclosure in service. A heat pump, by virtue of its design, operates in a damp condensate environment.
The evaporator coils pass large volumes of corrosive air; coils are constructed of a copper tube surrounded with aluminium fin stock. To maximise aluminium fin life, we insist that at a minimum, the coils be double epoxy dipped at the time of assembly.
Coils subjected to extremely harsh environments should be specified with copper fins.
You should expect an operational life of 5 years plus from an outdoor installation and somewhat longer from indoor. In service, we find that outdoor installations have the added problem of garden mulch build up around the base of the heater, which retains moisture and accelerates enclosure deterioration.
Most gas heaters have zinc anneal or galvanised steel enclosures and, because of their operating temperatures, are less susceptible to corrosion than heat pumps. Having said that, most gas heaters on the coast end their service life because of corroded enclosures.
Some manufacturers offer stainless steel enclosures, but taking into account the extra cost against the purchase price of a new heater, we find fitment hard to justify.
Heat Exchange (All)
A heat exchange, whatever their material make-up, is susceptible to corrosion or plating from unbalanced pool water.
It is important for the longevity of the heat exchange that you ensure that the pool water is maintained in line with the recommended saturation index. Pool operators should seek the assistance of a pool shop professional to make the necessary pool water adjustments.
There are so many variables to consider, like the size of the pool, location, projected bather load, the role the pool will play (commercial pool, hydrotherapy pool, swim school, domestic pool), all of which may have different outcome requirements. The use of a pool cover will also affect the operating costs.
With the above information, our staff at Billabong Pool Service & Supply can provide you with an accurate (depending upon the information provided) picture of the operating cost you could expect. There are also some very good online calculators available but are still reliant on the information provided.
Electricity pricing depends on the best negotiation with various electricity suppliers. Different tariffs can be applied after operating times and heating outcomes are considered. Contractual pricing should be considered, but with caution.
Gas pricing depends on best negotiation with the various gas suppliers. Volume users enjoy more attractive pricing and pricing varies between bottle and bulk supply. Contractual pricing should be considered, but with caution.
Billabong has a preferred product range, but we can supply most brands on request.
- Accent Air / Rheem Heat Pumps
- \Astral / Raypak LPG gas heaters
- Astral LPG heat exchanger systems
- Elecro resistance electric heaters
We are located at:
7 Kayleigh Drive, Maroochydore
Phone: 07 5443 2111
20 Rene Street, Noosaville
Phone: 07 5449 7855
134 Bulcock Street Caloundra
Phone: 07 5438 1577