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Swimming Pool Heating

By: Osama Khalil | 2 months ago

Swimming Pool Heating

Heating a swimming pool can consume a lot of energy and add up to high heating bills. You can improve your swimming pool's heating and energy efficiency by installing an energy efficient pool heater and by taking steps to reduce pool heating costs.

You can reduce the cost of heating your swimming pool by installing a high-efficiency or solar heater, using a pool cover, managing the water temperature, and using a smaller pump less often.

Swimming Pool Covers

 

Covering a pool when it is not in use is the single most effective means of reducing pool heating costs. 
You can significantly reduce swimming pool heating costs by using a pool cover.

Use of a pool cover also can help reduce the size of a solar pool heating system, which can save money.

HOW THEY WORK

Swimming pools lose energy in a variety of ways, but evaporation is by far the largest source of energy loss. Evaporating water requires tremendous amounts of energy. It only takes 1 Btu (British thermal unit) to raise 1 pound of water 1 degree, but each pound of 80ºF water that evaporates takes a whopping 1,048 Btu of heat out of the pool.

The evaporation rate from an outdoor pool varies depending on the pool's temperature, air temperature and humidity, and the wind speed at the pool surface. The higher the pool temperature and wind speed and the lower the humidity, the greater the evaporation rate. In windy areas, you can add a windbreak—trees, shrubs, or a fence—to reduce evaporation. The windbreak needs to be high enough and close enough to the pool that it doesn't create turbulence over the pool, which will increase evaporation. You also don—t want the windbreak to shade the pool from the sun, which helps heat it.

Indoor pools aren't subjected to the environment, but they still can lose a lot of energy from evaporation. They even require room ventilation to control indoor humidity caused by the large amount of evaporation. The ventilated air also must be conditioned, which adds to the energy costs.

Pool covers minimize evaporation from both outdoor and indoor pools. Covering a pool when it is not in use is the single most effective means of reducing pool heating costs. Savings of 50%–70% are possible.

Pool covers on indoor pools not only can reduce evaporation but also the need to ventilate indoor air and replace it with unconditioned outdoor air. You can also shut off exhaust fans when an indoor pool is covered, which saves even more energy.

TYPES OF POOL COVERS

Technically, all you really need for a pool cover is a large sheet of plastic. Plastic meets the requirement of being a vapor barrier. But a large sheet of plastic that you get from the lumber store is probably not your best choice. It will be very difficult to handle and store, it tears easily, and sunlight will deteriorate it rapidly. You can use a sheet of plastic, but it will be very inconvenient and it will probably only last 1 to 2 seasons maximum.

It's best to use a cover designed specifically for swimming pools. They're made of special materials, such as UV-stabilized polyethylene, polypropylene, or vinyl. They can be transparent or opaque. Covers can even be light or dark colored.

One of the lowest cost covers made specifically for swimming pools is the bubble (or solar) cover. Bubble covers are similar to bubble packing material except they use a thicker grade of plastic and have UV inhibitors.

Vinyl covers consist of a heavier material and have a longer life expectancy than bubble covers. Insulated vinyl covers are also available with a thin layer of flexible insulation sandwiched between two layers of vinyl.

Outdoor pools gain heat from the sun, absorbing 75%–85% of the solar energy striking the pool surface. This is an important contribution to the pool's heating needs. A pool cover will decrease the solar gain contribution to some extent, depending on what type you use. A transparent bubble cover may reduce pool solar energy absorption by 5%–15%. A completely opaque cover will reduce it by 20%–40%. You need to consider this when selecting a pool cover.

You also need to decide whether you want a manual, semi-automatic, or an automatic pool cover. You can manually pull the cover on and off, fold it, and place it somewhere out of the way. You can also purchase a pool cover reel to help manually roll up the pool cover. The reel, usually on wheels, can be rolled out of the way.

Semi-automatic covers use a motor-driven reel system. They use electrical power to roll and unroll the cover, but usually require someone to pull on the cover when unrolling, or guide the cover onto the reel when rolling up the cover. Semi-automatic covers can be built into the pool deck surrounding the pool, or can use reels on carts.

Automatic covers have permanently mounted reels that automatically cover and uncover the pool at the push of a button. They're the most expensive option, but they're also the most convenient.

Some pool covers fit into tracks along the sides of the pool. This prevents anything or anybody from getting into the pool. They even support the weight of several people. If liability is a concern, these are a good option to explore. They can be run manually, semi-automatically, or automatically. Safety covers are recommended for public pools, and may be required by inspectors.

HOW TO USE A POOL COVER

Pool covers should be used during your swimming season. If you use your pool during the daytime, take off the cover just before swimming and replace the cover as soon as you're done using the pool.

If you use your pool only at night, the effectiveness of a pool cover will depend on whether the evaporation and other losses prevented by the cover exceed the solar gain reduction caused by the cover. The type of cover and the climate affects this balance. In dry and/or windy conditions, the evaporation rate of the pool increases. Therefore, it is generally beneficial to have a transparent or bubble cover on during daylight hours. In warm, humid conditions the evaporation rate decreases. In this case, it may be more beneficial to leave the cover off during the daytime.

OTHER POOL COVER BENEFITS

Besides offering energy savings, pool covers also do the following:

  • Conserve water by reducing the amount of make-up water needed by 30%–50%
  • Reduce the pool's chemical consumption by 35%–60%
  • Reduce cleaning time by keeping dirt and other debris out of the pool.






 

 

Pool Heaters

Gas Swimming Pool Heaters

Gas-fired pool heaters remain the most popular system for heating swimming pools. Today you can find new gas-fired heater models with much higher efficiencies than older models. Still, depending on your climate and pool use, they may not be the most energy-efficient option when compared to heat pump and solar pool heaters.

How They Work

Gas pool heaters use either natural gas or propane. As the pump circulates the pool's water, the water drawn from the pool passes through a filter and then to the heater. The gas burns in the heater's combustion chamber, generating heat that transfers to the water that's returned to the pool.

They're most efficient when heating pools for short periods of time, and they're ideal for quickly heating pools. Therefore, gas pool heaters can be a good choice for pools that aren't used on a regular basis. Unlike heat pump and solar pool heaters, gas pool heaters can maintain any desired temperature regardless of the weather or climate.

Selecting a Gas Pool Heater

When selecting a gas swimming pool heater, you need to consider the following:

  • Size
  • Efficiency

Sizing a Gas Pool Heater

You should have a trained pool professional perform a proper sizing analysis for your specific swimming pool to determine pool heater size.

Sizing a gas pool heater involves many factors. Basically, a heater is sized according to the surface area of the pool and the difference between the pool and the average air temperatures. Other factors also affect the heating load for outdoor pools, such as wind exposure, humidity levels, and cool night temperatures. Therefore, pools located in areas with higher average wind speeds at the pool surface, lower humidity, and cool nights will require a larger heater.

Gas pool heaters are rated by Btu (British thermal unit) output. Outputs range from 75,000 Btu to 450,000 Btu.

To calculate an approximate heater size for an outdoor swimming pool, follow these steps:

  1. Determine your desired swimming pool temperature.
  2. Determine the average temperature for the coldest month of pool use.
  3. Subtract the average temperature for the coldest month from the desired pool temperature. This will give you the temperature rise
  4. Calculate the pool surface area in square feet.

Determining Efficiency of a Gas Pool Heater

New gas swimming pool heaters have a standard test they go through to determine their energy efficiency based on their Btu (British thermal unit) output.

Heater efficiency is the ratio of usable output to energy input. For example, an 80%-efficient heater uses $80 worth of useful heat for every $100 worth of fuel. Therefore, it wastes 20% of the fuel.

Most gas pool heaters feature their efficiency percentage on their nameplates. A pool heater's manufacturer can also provide its efficiency percentage.

Today, you'll find some gas pool heaters with 89%–95% efficiency. The following table shows how much you can save for every $1,000 in annual pool heating costs by installing a gas pool heater that's 95% efficient.


Installation and Maintenance

Proper installation and maintenance of your gas pool heater can optimize its efficiency. It's best to have a qualified pool professional install the heater and even perform complicated maintenance or repair tasks.

Read your owner's manual for a maintenance schedule and/or recommendations. You'll probably need to tune up your pool heater annually. Also, scaling in the burner or heat exchanger may decrease efficiency over a period of time.

With proper installation and maintenance, gas pool heaters typically last five or more yearsزز

 

 

 

 

Heat Pump Swimming Pool Heaters

How They Work

Heat pumps use electricity to capture heat and move it from one place to another. They don't generate heat.

As the pool pump circulates the swimming pool's water, the water drawn from the pool passes through a filter and the heat pump heater. The heat pump heater has a fan that draws in the outside air and directs it over the evaporator coil. Liquid refrigerant within the evaporator coil absorbs the heat from the outside air and becomes a gas. The warm gas in the coil then passes through the compressor. The compressor increases the heat, creating a very hot gas that then passes through the condenser. The condenser transfers the heat from the hot gas to the cooler pool water circulating through the heater. The heated water then returns to the pool. The hot gas, as it flows through the condenser coil, returns to liquid form and back to the evaporator, where the whole process begins again.

Higher efficiency heat pump pool heaters usually use scroll compressors versus the reciprocal compressors of standard units.

Heat pump pool heaters work efficiently as long as the outside temperature remains above the 45ºF–50ºF range. The cooler the outside air they draw in, the more energy they use. However, since most people use outdoor swimming pools during warm and mild weather, this usually isn't an issue.

Selecting a Heat Pump Pool Heater

Heat pump pool heaters cost more than gas pool heaters, but they typically have much lower annual operating costs because of their higher efficiencies. With proper maintenance, heat pump pool heaters typically last longer than gas pool heaters. Therefore, you'll save more money in the long run.

When selecting a heat pump pool heater, you should consider its:

  • Size
  • Efficiency

Sizing a Heat Pump Pool Heater

You should have a trained pool professional perform a proper sizing analysis for your specific swimming pool to determine pool heater size.

Sizing a heat pump pool heater involves many factors. Basically, a heater is sized according to the surface area of the pool and the difference between the pool and the average air temperatures. Other factors also affect the heating load for outdoor pools, such as wind exposure, humidity levels, and cool night temperatures. Therefore, pools located in areas with higher average wind speeds at the pool surface, lower humidity, and cool nights will require a larger heater.

Heat pump pool heaters are rated by Btu output and horsepower (hp). Standard sizes include 3.5 hp/75,000 Btu, 5 hp/100,000 Btu, and 6 hp/125,000 Btu.

To calculate an approximate heater size for an outdoor swimming pool, follow these steps:

  1. Determine your desired swimming pool temperature.
  2. Determine the average temperature for the coldest month of pool use.
  3. Subtract the average temperature for the coldest month from the desired pool temperature. This will give you the temperature rise
  4. Calculate the pool surface area in square feet.

Determining Heat Pump Swimming Pool Heater Efficiency

The energy efficiency of heat pump swimming pool heaters is measured by coefficient of performance (COP). The higher the COP number, the more efficient. However, there is no standard test for measuring the COP. Therefore, you really can't compare the COPs of different models unless you know that the manufacturers used the same test for each model. For example, the same heat pump will operate at a higher COP when the outside air temperature is higher.

Typically, manufacturers measure the COP by testing a heat pump pool heater with an outdoor temperature of 80ºF and pool temperature of 80ºF. COPs usually range from 3.0 to 7.0, which converts to an efficiency of 300%–700%. This means that for every unit of electricity it takes to runs the compressor, you get 3–7 units of heat out of the heat pump.

Installation and Maintenance

Proper installation and maintenance of your heat pump pool heater can optimize its efficiency. It's best to have a qualified pool professional install the heater, especially the electric hookup, and perform complicated maintenance or repair tasks.

Read your owner's manual for a maintenance schedule and/or recommendations. You'll probably need to tune up your pool heater annually. Because of a heat pump pool heater's many moving and electrical parts, it will probably require periodic service by an air conditioning technician.

With proper installation and maintenance, heat pump pool heaters can last 10 or more years.

Solar Swimming Pool Heaters

 

You can significantly reduce swimming pool heating costs by installing a solar pool heater. They're cost competitive with both gas and heat pump pool heaters, and they have very low annual operating costs. Actually, solar pool heating is the most cost-effective use of solar energy in many climates.

HOW THEY WORK

Most solar pool heating systems include the following:

  • A solar collector -- the device through which pool water is circulated to be heated by the sun
  • A filter -- removes debris before water is pumped through the collector
  • A pump -- circulates water through the filter and collector and back to the pool
  • A flow control valve -- automatic or manual device that diverts pool water through the solar collector.

Pool water is pumped through the filter and then through the solar collector(s), where it is heated before it is returned to the pool. In hot climates, the collector(s) can also be used to cool the pool during peak summer months by circulating the water through the collector(s) at night.

Some systems include sensors and an automatic or manual valve to divert water through the collector(s) when the collector temperature is sufficiently greater than the pool temperature. When the collector temperature is similar to the pool temperature, filtered water simply bypasses the collector(s) and is returned to the pool.

Solar pool collectors are made out of different materials. The type you'll need depends on your climate and how you intend to use the collector. If you'll only be using your pool when temperatures are above freezing, then you'll probably only need an unglazed collector system. Unglazed collectors don't include a glass covering (glazing). They are generally made of heavy-duty rubber or plastic treated with an ultraviolet (UV) light inhibitor to extend the life of the panels. Because of their inexpensive parts and simple design, unglazed collectors are usually less expensive than glazed collectors. These unglazed systems can even work for indoor pools in cold climates if the system is designed to drain back to the pool when not in use. Even if you have to shut the system down during cold weather, unglazed collectors may be more cost effective than installing a more expensive glazed collector system.

Example of how a solar collector works.

Glazed collector systems are generally made of copper tubing on an aluminum plate with an iron-tempered glass covering, which increases their cost. In colder weather, glazed collector systems—with heat exchangers and transfer fluids—capture solar heat more efficiently than unglazed systems.

Therefore, they can be used year-round in many climates. Glazed collectors also can be used to heat domestic hot water year-round.

Both glazed and unglazed collector systems should include freeze protection if they'll be used in colder conditions.

SELECTING A SOLAR POOL HEATER

A solar pool heating system usually costs between $3,000 and $4,000 to buy and install. This provides a payback of between 1.5 and 7 years, depending on your local fuel costs. They also typically last longer than gas and heat pump pool heaters. Your actual cost and payback depend on many factors. Therefore, before you purchase and install a solar pool heating system, you should do the following:

  • Evaluate your site's solar resource
  • Determine the correct system size
  • Determine the correct orientation and tilt for the collector
  • Determine the system's efficiency
  • Compare system costs
  • Investigate local codes, covenants, and regulations.

EVALUATING YOUR SITE'S SOLAR RESOURCE

Before you buy and install a solar pool heating system, you first need to consider your site's solar resource. The efficiency and design of a solar pool heater depends on how much of the sun's energy reaches your building site.

Solar pool heating systems use both direct and diffuse solar radiation. Therefore, even if you don't live in a climate that's warm and sunny most of the time -- like the southwestern United States -- your site still might have an adequate solar resource. Basically, if your building site has unshaded areas and generally faces south, it's a good candidate for a solar pool heating system.

Your local solar system supplier or installer can perform a solar site analysis.

 

 

SIZING A SOLAR POOL HEATER

Sizing a solar swimming pool heating system involves many factors:

  • Pool size
  • Length of swimming season
  • Average regional temperatures
  • Desired pool temperature
  • Site's solar resource
  • Collector orientation and tilt
  • Collector efficiency
  • Use of a pool cover.

Solar system contractors use worksheets and computer programs to help determine system requirements and collector sizing.

Basically, the surface area of your solar collector should equal 50%–100% of the surface area of your pool. In cooler and cloudier areas, you may need to increase the ratio between the collector area and the pool surface area. Adding collector square footage also lengthens the swimming season.

In any climate, you can usually decrease the required collector area by using a pool cover.

You'll also want a properly sized pool pump for a solar system. If you're replacing a conventional pool heating system with a solar system, you may need a pump larger than your current one or a separate, smaller pump to move the pool's water to and through the collectors.

SITING A SOLAR POOL HEATING SYSTEM'S COLLECTOR

Collectors can be mounted on roofs or anywhere near the swimming pool that provides the proper exposure, orientation, and tilt toward the sun. Both the orientation and tilt of the collector will affect your solar pool heating system's performance. Your contractor should consider them while evaluating your site's solar resource and sizing your system.

Collector Orientation

Solar pool heater collectors should be oriented geographically to maximize the amount of daily and seasonal solar energy that they receive. In general, the optimum orientation for a solar collector in the northern hemisphere is true south. However, recent studies have shown that, depending on your location and collector tilt, your collector can face up to 45º east or west of true south without significantly decreasing its performance. You'll also want to consider factors such as roof orientation (if you plan to mount the collector on your roof), local landscape features that shade the collector daily or seasonally, and local weather conditions (foggy mornings or cloudy afternoons), as these factors may affect your collector's optimal orientation.

Collector Tilt

The angle at which a collector should be tilted varies based on your latitude and the length of your swimming season (summer or year-round). Ideally, collectors for summer-only heating should be tilted at an angle equal to your latitude minus 10º–15º. Collectors for year-round heating should be tilted at an angle equal to your latitude. However, studies have shown that not having a collector tilted at the optimum angle will not significantly reduce system performance. Therefore, you can usually mount collectors flat on your roof, which might not be at the optimum angle but more aesthetically pleasing. You will, however, want to take roof angle into account when sizing your system.

DETERMINING THE EFFICIENCY OF SOLAR SWIMMING POOL HEATING SYSTEM

You can determine the efficiency of a solar swimming pool heating system based on the collector's thermal performance rating if available.

A solar collector's thermal performance rating is measured by Btu (British thermal unit) per square foot per day: Btu/(ft2day)

Or, the rating can be measured by megajoules (MJ) per square meter per day: MJ/(M2day)

It can also be measured by Btu per day, which is simply the rating in Btu/(ft2day) multiplied by the area in ft2. Also used is MJ per day, which is the rating in MJ/(M2day) multiplied by the area in M2.

The higher the number, the greater the solar energy collection efficiency. However, because weather conditions, instrumentation accuracies, and other test condition constraints can vary, the thermal performance of any two collectors should be considered approximately the same if their ratings are within 25 Btu/(ft2day) of each other.

High efficiency solar collectors not only will reduce your annual operating costs, but may also require fewer square feet of collector area to heat the pool.

COMPARING SOLAR SWIMMING POOL HEATING SYSTEM COSTS

Before purchasing a solar pool heating system, you can estimate and compare the costs of using different solar collector models. This will help you determine the potential cost savings of investing in a more efficient type of collector, which may require fewer panels for the collector area needed to heat your pool.

To estimate and compare costs, you need to know the following:

  • A collector's thermal performance rating(Btu/day)
  • Total number of collector panels or piping for the area needed to heat your pool
  • Total installed cost of system.

You can then calculate a collector's energy output per dollar spent or invested using this formula:

(Btu/day X # of collector panels/piping modules) ÷ total installed cost of system = Btu/$ per dollar spent

Example:

(27,900 X 4) Btu ÷ $3,000 = 37.20 Btu/day per dollar spent

If you just know the prices and thermal performance ratings (Btu/day) of collectors, you can use the following formula to calculate the energy output for each dollar spent or invested for different collectors:

Btu/day ÷ collector price = Btu/day per dollar spent

Example:

21,000 Btu ÷ $387 = 54.26 Btu/day per dollar spent

Don't choose a solar pool heating system or collector based solely on its estimated costs. When selecting a solar pool heater, it's also important to consider all of the factors involved in the system's sizing and quality of the design and installation.

BUILDING CODES AND COVENANTS

As with a solar water heating system, it is important to consider local building codes and regulations for solar water heating.

INSTALLATION AND MAINTENANCE

The proper installation of a solar pool heating system depends on many factors. These factors include solar resource, climate, local building code requirements, and safety issues. Therefore, it's best to have a qualified solar thermal systems contractor install your system.

After installation, properly maintaining your system will keep it running smoothly for 10–20 years. Consult your contractor and read your owner's manual for maintenance requirements. Your collector should require little maintenance if the pool's chemical balance and filtering system are checked regularly. Glazed collectors may need to be cleaned in dry climates where rainwater doesn't provide a natural rinse.

 

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