Bluepools

Heat Pumps and Sustainable Heating Systems


I. The Heating and Environmental Control of Indoor Swimming Pools

The Problem - At certain times the ambient temperature changes in the UK can amount to over 10 degrees C in an hour or so and at such times as much as 80kW of power is required to maintain a comfortable temperature in a large pool hall

Providing this amount of heating energy in an hour or so from sustainable energy sources is very difficult using current technology. The only way that it can be provided is by the storage of hot water in a tank or by the installation of a sustainable energy source that is much too large and costly for day to day use.

This applies to both Ground Source and Air Source Heat pumps.

Both types are ideal for day to day use but will not provide the energy required to maintain constant levels of Air and Water temperature in a pool hall when the external ambient air temperture drops suddenly. Hence the best answer is to size up the sustainable energy source based on day to day requirements and to install a small gas (natural, butane or propane) or oil fired boiler that will only be used a few times a year at most and hence cost a negligible amount to run. Where this is impracticable because only electric power is available a larger hot water storage tank with an immersion heater will also prove very economical to install and run because of the low capital cost and very occasional use.

 

II. How Air Handling Units (AHU's) control the Heating and Environmental Conditions in an Indoor Swimming Pool Hall

The quality, healthiness and comfort of the air and water environment in a pool hall of the air depends entirely on the Air Handling Unit.

These complex machines control the following environmental interdependent conditions in a pool hall:

The heat in a pool hall is mainly provided through heating the pool water in a heat exchanger inside the AHU but many AHU's can also directly heat or cool the air as it passes through the AHU as part of the dehumidification process.

 

AHU Functions

The AHU controls the Pool Hall environment by carrying out the following processes:

  1. Extracts air from the pool hall through a large low level intake grill (Air humidity is maximum at low level over the pool water)
  2. Extracts the heat energy from the air
  3. Discharges a proportion of the air to waste outside the building (the pool hall air is changed about 6 times per hour)
  4. Takes in fresh air to replace the waste air and heats it using the energy extracted from the humid pool hall air
  5. Adds additional heat (or cooling) as required by the air and water temperature settings on the AHU (set by pool owner)
  6. Discharges warm dry air back into the pool hall by floor mounted diffusers that create a curtain of warm dry air in front of any glazing in the pool hall (stops condensation)
Bluepools designs the Schemes and ensures that the Capital Cost is returned in Reduced Pool Operating Costs

Such equipment will require significant investment and Bluepools will not only design a scheme that will actually work - but also make sure that the capital cost is returned by reduced operating costs.


III. Types of Equipment

How to harness the Sun's energy that falls on the Earth's surface?

The different types of equipment fall into three categories that are of practicable use in a swimming pool:

  1. Air Source Heat Pumps that Heat Water
  2. Ground Source Heat Pumps that Heat Water
  3. Photo-Voltaic cells that produce Electricity

Nothing else is viable because direct Solar Heating of water does not work in Northern Europe (Including France) because of the unreliability of the weather in Spring and Autumn.


Local Authorities are insisting on "Renewable Energy" heating systems:

All these systems should be welcomed by Local Authorities who are insisting on "Renewable Energy" heating systems that will comply with the current Building Regulations.

Both types 1 and 2 are ideal for supplying the required Hot Water to the Air Handling Units that control and regulate the Environment in an indoor pool hall, including both air humidity and air and water temperatures.

Roof mounted Photo-Voltaic cells reduce running costs even more but are of course quite costly to install.

 

IV. Air Source Heat Pumps

How do they work?

Air Source Heat Pumps absorb energy directly from the external air rather than from the earth's strata which eliminates the need for heat collector pipework in the ground.

Air to water heat pumps have been successfully installed for many years, especially for providing very efficient pool water heating.


COP (Coefficient of Performance):

The efficiency of both air and ground source heat pumps is expressed as a number - normally between 2 and 6. This number provides the energy output of the heat pump as a multiple of the energy required to run the electric motors that power the compressor and fans etc within the heat pump.

So a heat pump with a COP of 4 will provide 4kW of energy for every 1kW that is needed to make it work.


Air Source Heat Pump Disadvantages:

The disadvantage of air source heat pumps is that the heat pump's coefficient of performance (COP) reduces when the air temperature is low.

During the colder months the outside air temperature is often less than the ground temperature (at a depth at which heat is extracted by a ground-source heat pump). This lower temperature has the effect of reducing the COP of an air source heat pump.


Ground Source Heat Pumps Cost a Lot More:

However, Ground Source Heat Pumps are a lot more costly to install because of the installation of underground pipework.


Better quality Air Source Heat Pumps provide the Best Value for Money:

Better quality Air Source Heat Pumps will provide a lot more heating power and last several times as long - and spare parts will always be available.

There are many types of air source heat pump being sold today and the cheap ones will work on a small outside pool for the summer months and may even last 2 or 3 years but spare parts for them are often unobtainable.


V. Ground Source Heat Pumps

How do they work?

These machines provide the means to collect the sunlight energy that falls on the earths surface which is then transferred deep underground by the thermal conductance of the surface layers and rock below.

The transfer of heat down into the deep layers is quite slow and as a result the temperature of the ground about 20 metres below the surface is constant all year round no matter how much the temperature of the surface layer varies between summer and winter.


How are they installed?

The Heat Collector pipework can be installed in shallow excavations where the heat energy available will be high in the summer and low in the winter or in deep boreholes where the heat energy availability is constant throughout the year.


Deep boreholes are a lot more complicated to design & install - get it wrong & the ground will freeze up!

The deep borehole options are much more expensive than the shallow borehole option and are a lot more complicated to design and install.

If the borehole is not deep enough and the ground around cannot provide enough energy to sustain the the transfer rate of the Ground Source Heat Pump the rocks around the borehole will get colder and colder until the ground freezes and the heat pump stops working!


Open Loop & Closed Loop Systems:

There are two basic options in deep borehole GSHP installations. These are known as Open Loop and Closed Loop.

In an Open Loop system there are two boreholes at least 7 or 8 metres apart and water is pumped up from one borehole, through the GSHP and down into the the second borehole where it is dispersed back into the ground.

In a Closed Loop system there is only one borehole and a pipe that goes down to the bottom and back up to the top and water is pumped through the pipe and through the GSHP where the heat energy is extracted.

It is easier to get consent for Closed Loop systems because there is no actual removal of water from the underground aquifer.

In most cases Open Loop Schemes will require a licence that is issued by the Environment Agency. Please click here for more information on this.


An extremely complex design process:

The design of Open & Closed Loop Systems is dependent on the thermal conductivity of the rock into which the borehole is driilled and the thermal conductvity depends on the water content of the rock and the groundwater levels and gradients. This is why the design is so complex and easy to get wrong if carried out by inexpereinced people.


Bluepools Design and Manage the installation:

Bluepools can design and manage the installation of Ground Source Heat Pump Schemes and make sure that the heat output exactly matches the requirement of the Air Handling Unit within the Pool Hall.


VI. Photo-Voltaic cells that produce Electricity

There are two types that can be used on the roof of a Pool Hall:

  1. Building Integrated Photo-Voltaic cells
  2. Photo-Voltaic cells

BIPV cells actually form the waterproof layer of the roof.

Conventional PV cells are fixed above the tiles or slates of the roof with fixings that are designed to maintain the weatherproofing of the building.

BIPV roofs are quite costly but can provide a loot of power up to a maximum of about 7kW per square metre.

Romag were the pioneer for these systems.