Earth Bonding in Domestic Property

Electricity is something we all take for granted. It is the unseen force, a stream of moving protons and electrons, which powers our machines and appliances. Perhaps the only time we give it much thought is when we receive the bill for consuming it.

However, this force, safely restrained within insulation cables, can be extremely dangerous if it is allowed to behave naturally. Electricity continually seeks to dissipate its energy by escaping from a circuit and flowing to earth.

This natural tendency is all well and good. So long as a person does not form part of a pathway allowing it to do so. A flow of electricity passing through a person to earth is commonly referred to as an electric shock.

In passing through any material towards earth, including a person, the electricity encounters resistance. Overcoming the resistance generates heat. This heat causes severe internal and external burns as it passes through a person. The flow of electrons also interferes with the natural electrical activity in the body causing severe damage and possible death.

Electricity will always find a route to earth that offers the least resistance. Faced with the option of a copper earth wire and human flesh, the electricity will choose the earth wire, plus a bit of the flesh.

In an attempt to prevent electrical shock, or damage to appliances caused by a sudden surge in electrical current, all circuits carry a fuse system. A surge in electricity will break the resistance tolerance of the fuse causing it to melt and cut the circuit. The fuse acts as the first line of protection in electrical circuits.

Domestic electrical circuits have to incorporate an earth circuit (PE).

In electrical terminology, earth is represented as ‘T’. This ‘T’ can take a number of forms. An earthing rod buried into the external ground of a property and forming an earth circuit through the electrical appliances would be referred to as ‘TT’. External earthing rods can be poor earth devices. A good earth requires a good contact with earth. The soil around earthing rods can dry out, shrinking away from the rods and causing poor earth contact.

Most homes utilise a TNC-S earthing system. ( N=nuetral, C=Combined, S=Separate) or better known as PME (Protective Multiple Earth).

With PME, earthing is carried by the supply company’s main earth back to the nearest sub-station. This earth is particularly good and reliable.

Bonding, on the other hand, is designed to prevent a disparity between electrical voltages if a fault occurs. Where a sudden release of electricity flows from an appliance, prior bonding of the metal in that appliance to other circuits that could contribute to creating alternative earth paths limit’s the voltage change potential.

There are two types of bonding, main bonding, and supplementary bonding.

Main bonding provides an interconnection between incoming metallic services such as gas and water. It is on these services that the householder will generally find the usual earth bonding yellow and green wires clamped to the pipe-work. There will also be main bonding joined to any metal fabric of the home, such as supporting iron and steel building construction materials. This earth bonding also provides protection in the event that it is the supplier’s earth that is causing the problem.

Supplementary or cross-bonding joins together metal components that could provide a circuit to earth, for instance if a fault developed on a towel rail in a bathroom and resulted in its surface becoming ‘live’, a person touching it and also touching a tap at the same time would form a circuit. Supplementary bonding links the earth across all these metal surfaces to reduce the destructive force of an electric shock. These bonding clamps can be seen on pipes and other metallic connections in bathrooms etc.

The final safety device in the home is performed by Residual Current Circuit Breakers (RCB’s). These devices monitor and detect changes in the steady and balanced flow of electrical current through the positive and negative wiring supply to appliances. A sudden leakage to earth, whether it be by an electric shock or other means of dissipation, will be detected almost instantaneously by the RCB. This will cause the RCB to operate (trip) and immediately break the circuit, significantly reducing the potential for harm or damage.

Although the complexities of earthing and bonding are possibly beyond the scope of DIY enthusiasts, the importance of supplying and maintaining them is not. It is most important that where a homeowner undertakes any remedial work to the property, or to the plumbing and electrical components, that earthing is provided and maintained.

When installing plastic pipework into a copper plumbing network, it is important to ensure that electrical bonds are maintained. This may entail building a bonding bridge between the plastic pipes and the continuation of the copper network to facilitate continuity.

Likewise, when working on pipe-work, cutting into a section of copper pipe during plumbing work will interfere with the bonding circuit. It is a wise precaution to temporarily provide a bonding bridge for electrical safety reasons.

Installing supplementary and cross bonding wiring is a simple procedure. Clamps and regulation-sized earth wire are easily obtainable from DIY and electrical suppliers. Bonding cables must run unbroken and continuous to the main earth block in the mains domestic consumer box, or the dedicated earth block located near it. It is possible to link supplementary bonding cables across platforms, such as bath taps to shower to towel rail, but main bonding must be continuous.

Homeowners should periodically check main and supplementary bonding cables and clamps to ensure that they continue to provide secure and serviceable operation. Any earth or bonding cable that becomes detached must be immediately replaced.

Although attaching earth and bonding connections does not carry any restrictions under the Building Regulations, anyone undertaking such work should make themselves acquainted with BS 7671 of the Wiring Regulations.

As always, any electrical work must be performed competently. Insurance cover may be affected by problems caused by substandard work. It is most important to seek professional advice when attempting to work on electrical installations. Building Regulations state that only certified persons can carry out electrical installation work.

What is a Passivhaus?

If you are like me, you have probably become very energy conscious. Conscious about the increasing cost, conscious about the environmental impact of obtaining energy and using it and conscious of not being able to afford to use it, full stop.

It was interesting to note that British Gas recently reported a fall in fuel demand for last winter. They attributed this to a mild winter. I do not recall the winter as being particularly mild. Rather it being not as cold as some. Winter is generally cold.

I doubt I am alone when I really do have to consider very carefully when, or indeed, if, I turn on the central heating at all.

Current energy policy in the UK seems to focus on supplying a potential for increasing energy consumption through investment in renewables and the development of controversial energy techniques such as fracking.

Increasing domestic energy costs to fund the development of intermittent energy sources and the exploitation of ever-diminishing fossil fuel reserves, may have the undesirable effect of reducing domestic energy consumption.

This causes untold misery for countless households that have little alternative other than to live in buildings that, by design, are not particularly energy efficient. Even new homes that are being built today and marketed as zero carbon are still significantly less energy efficient than a Passivehause.

A Passivehause, or passive house, uses innovate design and building materials to minimise energy consumption, reducing it to almost negligible levels whilst maintaining enhanced comfort levels within the building.

First developed in Germany in the 1990′s, a Passivehause works with its environment rather than imposing upon it. The building is specifically designed to be rigorously energy efficient. This allows it to conserve heat rather than relying on a constant supply of energy to maintain a comfortable living environment.

Building a Passivehause requires a complete shift in the current and traditional approach to building design and construction methods. Each passivehause must be individually designed from the ground up, and it must also take into account its location and the surrounding environment.

Using intelligent design in conjunction with a specialised computer software package, The Passive Hause Planning Package (PHPP), building designers and architects can fine-tune their designs.

Imputing various characteristics into the programme helps the designer to manipulate and modify the structure to maximise the energy efficiency of the building.

Although there are no set standards that must be adhered to, a Passivehause relies on a set of voluntary performance standards that accommodate many different ways of meeting the criteria for the Passivehause classification.

The design of the building requires that no thermal bridges are present in the construction. Thermal bridges conduct internal temperatures to the external environment and vice-versa.

Window construction must be of a superior design, typically triple glazed, filled with argon or krypton gas and the frames bonded into specialised insulation material to prevent heat transfer. The windows must provide a U-value of less than 0.8.

The building has to be encased in a quality insulation material, usually 300mm thickness and the building must be built to create an airtight internal environment. Some specialist insulation materials contain internal air pockets that enhance the insulation capabilities.

The building must optimise the heat from the sun and retain it along with heat generated by the activities of the occupants.

Ventilation is provided through a manual ventilation heat recovery system (MVHR) which must reclaim a minimum of 80% of the heat from extracted air and transfer that heat back to incoming air via the heat exchanger.

In order to meet the standards required for a building to be classed as a Passivehause, the heating requirement of the building must not exceed 15kWh/m/yr. In comparison, the maximum heat requirement set for a zero carbon new home for 2016 is 46kWh/m/yr.

The air changes in a Pasivehause must not exceed 0.6 times the entire house volume in one hour.

Consequently, the complete heat requirement of a Passivehause can be met by a small space heater supplied by a ground source heat pump and supplemented by solar energy. However, supplementary heat can be provided by gas boilers so long as the maximum kWh requirements are not exceeded.

Of course, each building will have different requirements dependent on the position of the building and the environment in which it is built. Building a Pasivehause at a latitude above the 60 line (London 51L) will increase costs due to greater insulation requirements and added design features such as underground heat storage facilities. This underground facility can reverse the conventional ground source heat pump technology to conserve summer heat for winter usage and vice-versa.

In general, the basic design and building costs are increased by at least 10% above conventional building costs. However, considerably more time is spent in the design process than current buildings require. Construction time is often minimised by the utilisation of pre-fabricated components.

Perhaps one of the most interesting facets of a Passivehause is the required change in the of the behaviour of the occupants. Any desire to open windows, such as for sleeping at night time has to be removed.

Once built, a Passivehause cannot be modified by expanding it, or by building extensions to it. Even fitting a satellite dish would seriously interfere with the structure by creating a thermal bridge. The occupants need to treat the building as a machine and co-exist with it.

Although not a particularly practical idea from a construction and financial position, it is possible to achieve Passivehause status in the renovation of an existing property, but in general, it is more economical to plan and develop one from scratch.

Nevertheless, as an alternative solution to energy concerns, a Passivehause construction produces superior comfort living environments for occupants at miserly energy consumption levels.

Passivehause status can be confirmed and certified by the Passivehause Institute following subjecting the property to a number of tests, but in practice, few Passivehause owners require that confirmation.

The principles utilised in domestic Passivehause construction can also be transferred into the design and construction of industrial facilities.

Great news for energy consumers, bad news for energy suppliers and governments.


Backflow in Plumbing

Clean, wholesome drinking water. We can take it for granted. Turn on the cold-water tap and it is there.

Wastewater. The grey soup from washing machines, washbasins, baths, and showers. It disappears down sinks and drains never to be seen again.

It would seem quite important that the two should never be allowed to mix and be inadvertently consumed by members of the household, or indeed other unsuspecting households connected to the supply.

Yet without precautions, clean water can become contaminated with materials that can have serious implications for human health. Toxic chemicals and dangerous micro-organisms can infiltrate domestic water supplies if suitable barriers are not in place to prevent them doing so.

The importance of maintaining an effective barrier between clean (potable) drinking water and the water using devices and appliances connected to the mains supply within the home should not be under-estimated. There are thousands of domestic water contamination incidents recorded each year, with some resulting in fatalities.

The biggest cause of problems involving domestic potable water contamination results from cross-connection issues. A contaminated source of water has the potential to be drawn into the clean water supply when it is connected to it. For example, a garden hose connected to the water supply could create a cross connection. If the flow of water through the connected hose is induced in the opposite direction this is referred to as backflow.

There are numerous cross connection unions in the typical home, from dishwashers and washing machines to combi boilers and mixer taps.

Backflow can be initiated by a number of adverse conditions such as a burst water main causing a sudden drop in pressure, a high demand for water on a supply line or frozen pipes interfering with the flow.

There are two main types of backflow. Siphonage and backpressure.

Siphonage may occur when the pressure of the mains water is not great enough to overcome the tendency for water to flow to its lowest level. For example, when siphoning a liquid from one container to another, a vacuum is created within the siphon tube by removing the air. So long as the siphon tube exit is positioned at a lower level than the level of the siphon tube entrance, the liquid will flow to its lowest level. This facilitates the flow of the liquid from one container to another.

Likewise, a garden hose with one end attached to the mains water supply and the other left submerged in a garden pond has the potential to contaminate the mains supply by the process of siphonage.

Backpressure is caused where the pressure in a system connected to the mains supply is able to overcome the mains pressure supplying it. For example, when water is heated by a combi boiler the water expands. As a result, the increased pressure has the potential to overcome the mains water pressure and cause a reversal of flow back into the mains water system. The same thing has the potential to occur with central heating fluids if the filling loop is left in place in the absence of a backflow prevention device.

The Water Supply (Water Fittings) Regulations 1999 makes the fitting of backflow prevention devices and techniques mandatory. The regulations also make it incumbent on the homeowner or a competent engineer, to install and maintain systems to comply with the regulations. They must prevent contamination and also give notice to the local council of any installation work that falls under The Buildings Regulations notification requirements.

The type of prevention device or method that must be employed can be established by referring to the list of water categories set out in the regulations. This list categorises the seriousness of contamination fluid risk on a score of one to five, with five being the most serious.

The simplest method of backflow prevention is to create an air gap. This is very effective and can be seen in operation with kitchen taps, sink taps, and toilet cisterns. The distance provided by the air gap is determined by the risk as set out in the regulations.

A tundish can also act as a backflow prevention device by virtue of the air gap it produces.

For direct connection, and in compliance with the necessary precautions determined by the Act, check valves, either single or double provide an effective barrier against potential contamination risks. These are easily fitted into the pipe-work where connections are made. A garden tap is required to be fitted with a check valve between a hose connection point and the tap bib.

Other forms of backflow prevention include ball valves in water storage tanks, where the water outlet must be above any overflow outlet, and integral protectors, such as are often found in mixer taps and non-return valves.

Reduced pressure zone valves (RPZ) may also be installed where required, but must be installed by a competent person.

Although it is not always necessary to fit check valves on mixer taps that do not have integral protectors, it is advisable.

It is also important to remember that tap outlets are a prime source of contamination and should be regularly cleaned. It is not uncommon to see contaminated material being placed in contact with the outlet or splashing back into it. Microbiological contaminants can thrive on tap outlets and contaminate further supplies.

When purchasing fittings it is important to ensure that they comply with the Water Regulations. It is not illegal to sell fittings that do not comply, but it is illegal to fit them.

The Act also stipulates that any fittings are installed in such a manner that they are easily accessible for maintenance and are adequately protected against frost.

The Water Regulations Advisory Scheme (WRAS) can provide copies of the Water Regulations (Water Fittings) Act 1999 and provide advice regarding compliance and the suitability of fittings.

Pipe Freezing Kits and Machines

Sometimes it can be the simplest job, such as changing a tap washer. At other times, it can be something slightly more complex, perhaps changing a radiator valve. Whatever the task, the thought of having to mess around trying to turn off a seized mains stopcock or drain down a central heating system, can initiate a certain amount of procrastination.

At other times, an urgency such as the repair of a burst pipe might be frustrated by the inability to locate either the domestic or the water provider’s main stopcock.

Whichever, the process of freezing and creating a plug of water in the supply pipework to temporarily interrupt the flow can be a quick and efficient method of facilitating a plumbing procedure.

Using a pipe freezing process is ideal for cutting the water supply in the immediate area to allow for the plumbing of T-pieces for appliances, radiator valve changes, pump and zone valve replacements. It can even facilitate the repair or replacement of a seized mains stopcock.

Pipe freezing can be accomplished by using refrigerants provided by disposable aerosol canisters or by specialised, electrically operated portable machines.

Aerosol canisters are designed to operate in conjunction with a dedicated kit. This kit comprises of thermal sleeves that wrap around pipework and valve connector attachments with refrigerant delivery tubes. These sleeves are usually made of durable nylon material.

Thermal sleeves come in a variety of sizes to fit the common pipe diameters in use today. The thermal sleeves act as a barrier to contain the evaporate and to delay thawing.

The refrigerant is a volatile gas that has been compressed to form a liquid and then held in that state under pressure in the canister. It is the sudden reduction of pressure that enables the liquid to return to its gaseous form. In doing do, it draws heat from its surroundings. This causes the freezing action.

For plumbing purposes, the thermal sleeves are applied to pipes and the liquid gas introduced where it evaporates to form an ice plug close to the working area, and if necessary, at a point beyond to prevent backflow. There should be a distance of at least 200 mm between the working area and the sleeve (s).

The process works best on horizontal pipework, but can be used on a vertical pipe.

There must be no flow of water through the pipes at the time of freezing, as this would inhibit the formation of an ice plug. Boilers and pumps must be turned off and leaks temporarily patched. The water in the pipes must also be cold, with the ambient room temperature below 20 degrees C for optimum efficiency.

One end of the flow pipe for the refrigerant is attached to the thermal sleeves, which in turn must be securely fastened to the plumbing pipework. The other end of the flow pipe is attached to a valve located on the canister. By operating the valve, the liquid under pressure in the canister passes down the tube into the thermal sleeve, where it expands and converts into a gas. This causes water in the plumbing pipe to freeze and form an obstructing plug of ice. The obstruction blocks the water flow. The refrigerant should be delivered in short bursts to prevent wastage or overspill. The thermal sleeves must remain in place until the plumbing work is completed. A naked flame and blowtorch cannot be used and plumbing fittings that are to be installed must be of compression or other non-heat requiring types.

Depending on the pipe-work material and diameter, and the ambient temperature of the water and room, the plug will form in copper pipes in around five minutes. Plastic pipes will take up to twenty minutes. An audible click from the device will inform the user that the plug has formed and that the plumbing work can commence. The ice plug will effectively prevent water flowing for about thirty minutes although it is possible to maintain the plug with further bursts of refrigerant.

It is important to ensure that there is sufficient aerosol refrigerant to complete and prolong the plumbing if it becomes necessary. The aerosol and gases produced must be used in a well-ventilated area. The refrigerant will cause serious burns if it comes into contact with skin or eyes and must not be inhaled.

Pipe freezing machines are an alternative to using a disposable canister. The principal of freezing the pipes is similar, however, the gas evaporation and re-pressurising is contained within the machine and is much safer to use. It is also environmentally friendly as no toxic gases are released into the atmosphere.

The machines are electrically operated and will supply and maintain a freezing process to pipes indefinitely, so long as the power supply is maintained.

The refrigerant is delivered via pipes to clamps attached to the pipework. The freezing process and maintenance are automatically controlled by the machine, which will also indicate when the ice plug has been formed. The clamps and the freezing process must remain in place until the work is completed.

There is a variety of machines on the market and manufacturers make machines that are capable of freezing any diameter of a pipe. The larger machines are regularly used by water companies to complete major pipe maintenance work.

Pipe freezing machines are expensive to purchase but can be hired on a daily basis from plant and tool hire companies. Currently, expect to pay around £50/day.

Both methods of freezing pipes for plumbing purposes are very effective if the manufacturer’s instructions are followed. Occasionally, where pipes are located in confined spaces, or very close to walls, neither conventional sleeves nor clamps can be effectively used. With pipe freezing machines there is a type of clamp that is held in place by rubber straps. The clamp freezes one side of the pipe and will take longer to form an ice plug. However, this can be used effectively where a normal clamp may not fit.

When cutting pipes to facilitate plumbing work, consider implications surrounding earth-bonding issues with electrical supplies.

For a one-off job, pipe freezing aerosols, and the kits that are available to facilitate their use may be the most practical option. Inclusive kits vary in price depending on size and the required application. A very simple kit can be purchased for around £30. Fittings and gas canisters can also be purchased individually. The kits and accessories are widely available from plumber’s suppliers and DIY outlets.



How to Repair the Main Stopcock

The house stopcock, or shut off valve, controls the mains flow of cold potable water into the property. It is commonly located under the kitchen sink although it may also be installed near a front door, in a cupboard, or even under a floorboard. It would be uncommon to find more than one stopcock controlling the mains water supply into an individual property.

Most stopcocks have to be manually operated, although there are now some being installed that are electronically operated. Electronically controlled stopcocks require specialist maintenance and should not be serviced by the householder.

It is most important that the householders are able to locate, identify and operate the manual stopcock. This is because it is the most practical way of closing off the pressurised mains water supply into the property. This would need to be carried out quickly in the event of a water leak or burst pipe within the property. It might also need to be operated to facilitate water appliance repairs or installations.

Perhaps the biggest problem that occurs with mains water supply stopcocks is the inability to turn them off. This is due to infrequent use. Without a frequent operation, the internal mechanism becomes affected by mineral particles and substances produced by the effects of metal corrosion. These adhere to the surfaces of the moving parts. Over time, this causes the washer and jumper mechanism to seize up. The crutch head becomes very difficult, if not impossible to turn. In the panic of a plumbing emergency, it is not uncommon for a householder to apply excessive force to the crutch head of a seized stopcock. Unfortunately, this can result in the crutch head shearing off from the spindle, leaving the valve in the open position.

It is also important to ensure that the operative knows which direction of turn opens and closes the stopcock. It is not unusual to find a householder has sheared off the crutch head by applying excessive force in the wrong direction.

Anti-clockwise opens. Clockwise closes.

To prevent problems occurring with a stopcock, it is a good idea to turn it on and off regularly. This will help to prevent a build up of material and ensure that the mechanism operates freely. It is also a good idea to turn a freely operating stopcock fully on, and then give it a half turn clockwise and leave it at that position. This will provide a little extra play on the device should it become stiff to operate in the future.

To free a seized or difficult to operate stopcock, spray a little penetrating and lubricating oil onto the spindle and gland nut, and then leave it to seep into the mechanism. This should solve the problem. If that does not work, slacken the gland nut and apply the spray again. If the stopcock still refuses to operate, a small amount of force can be applied to the crutch head using a wrench.

Occasionally, applying a carefully directed blowtorch flame to the gland nut will provide just enough metal expansion to free the seized mechanism. It is a wise precaution to clean away any surplus penetrating oil before doing so.

If all attempts to free a seized stopcock fail, the water supply can be turned off at the water supplier’s main valve. This will usually be located outside the homeowner’s boundary. It may be on the pavement under a small iron cover marked SVS, or it may have the water suppliers identifying mark. Sometimes this valve is a normal stopcock, but more often than not it is a spindle headed valve that requires a specific tool to operate it. This can be obtained from tool hire firms.

Alternatively, the water supplier will attend to operate the device. This mains stopcock is the property of the water supplier and its maintenance and operation are technically their responsibility.

On some networks, turning off the water supplier’s mains water valve will affect other residents. They should be forewarned about any interruption to their supplies.

Turning off the water supplier’s mains supply valve will facilitate the repair or replacement of the domestic water stopcock. It is quite feasible for a competent DIY enthusiast to strip down and service a mains stopcock or to remove and install a new one. However, the location of the stopcock may make access and work on it difficult due to restricted working space.

When removing and replacing a domestic mains stopcock, there will be a significant amount of water and pressure remaining in the system when the supplier’s valve has been turned off. This pressure can be released by turning on the domestic cold-water tap. Unless a drain valve has been installed close to the stopcock, a suitable receptacle will be required to collect any surplus water draining from the pipe above the stopcock.

On other occasions, a householder may become aware of a slow leak from a stopcock. Left unattended, a small leak can cause substantial damage to the fabric of a property. The most usual causes are leaking compression nuts or deterioration of the gland packing material.

Leaks from the compression nuts can be addressed by gently tightening the nuts. Care should be taken to not over-tighten compression nuts, as this will interfere with the correct operation of the stopcock. The stopcock should be held firmly with a set of grips whilst tightening the compression nuts to prevent fracturing the attached pipe-work.

Leaks from the gland head can be rectified by trying to tighten the gland nut. If that fails to stop the leak, removing the crutch and unscrewing the gland will allow the householder to clean away any detritus and old packing material. It is not necessary to turn off the water supplier’s main valve to accomplish this task. PTFE tape can then be gently wound around the exposed area of the spindle and prodded down into the gland area with a screwdriver. The gland nut and spindle can then be re-attached.

In general, the regular inspection and operation of the domestic mains stopcock will ensure problems do not occur, or only become apparent in an emergency.

Because of the substantial damage that can be caused by unmanageable releases of water under mains pressure and the subsequent insurance implications, if there is any doubt over issues relating to competency, professional assistance should be sought in relation to stopcock operating issues.

Gas-Fired Absorption Heat Pumps

Whilst high-efficiency gas condensing boilers are currently the norm for new domestic water-heating installations, an attractive alternative is currently under development.

Heat pumps, in general, have slowly gained acceptance in the UK. The practice of extracting ambient heat energy from the environment and then concentrating it into a usable heat source has been around for many years. However, in the early days, the size of the equipment required for the process limited its application to the heating of commercial or large building structures.

Gradually, technological advancements enabled the size of the installations to be dramatically reduced, making them suitable for domestic utilisation. The move towards promoting renewable energy alternatives ensured that the uptake of heat pumps and the research into more efficient systems continued.

Vapour compression heat pumps are now becoming widely used in domestic situations to provide under-floor heating and supplement domestic hot water supply systems.

Although the installation of vapour compression heat pumps marks a considerable leap forward in attitudes towards reducing CO2 emissions and reducing fossil energy consumption, there has still been a level of concern about the use of HFC refrigerants as the internal heat transfer medium. Concerns about the escape of HFC compounds into the atmosphere have acted as a deterrent when considering the installation of heat pumps.

In addition, the need to compress refrigerants in vapour compression heat pumps requires electricity to operate a compressor. This reduces the overall energy efficiency factor.

Vapour compression heat pumps are designed to provide lower temperature background heating through a large surface area heating element that heats from ground level upwards.

Conversely, a condensing boiler produces high-temperature water that circulates through the relatively small surface area of radiant and convection heat emitters.

What is needed is a heat pump that can extract sufficient heat from the external ambient environment and convert it into a high-temperature energy source. This could provide copious domestic hot water at the required temperature plus enough surplus heat to power the installed central heating system.

Gas fired heat pumps are likely to provide the solution. They have been used extensively to heat large buildings. Now they are being developed and pioneered as the appliance that could consign condensing gas boilers to history.

Unlike their vapour compression counterparts, gas fired heat pumps use natural gas as a heat source to drive an extremely efficient heat collection and transfer system.

The principle at the heart of gas-fired heat pumps is the process of using a generator-absorber heat exchange cycle.

In this cycle, ammonia is used as a refrigerant or generator, and water acts as an absorber in the process.

A gas burner heats a water and ammonia solution contained within a closed loop system. This evaporates the ammonia, which turns to a gas. The ammonia gas under pressure passes into a condenser. In condensing, it releases heat, which is recovered to supply the domestic system. In condensing, it also becomes low-pressure ammonia in a liquid form. This liquid ammonia needs to evaporate and to do so; it draws heat from the ambient external air. In doing so, it becomes absorbed back into the water and returns to being a water-ammonia solution. This continual process powers the operation acting as a pump.

Because of this mode of operation, the system has no moving mechanical parts. This means that maintenance is negligible. It also means that the system operates quietly and unobtrusively.

The heat recovered from this process is considerably higher than the gas heat input required to operate the burner. The process delivers hot water in excess of 65 degrees centigrade. This is quite adequate for all domestic requirements.

The advantage over a condensing boiler is that the hot water has been produced by using a fraction of the amount of gas that a condensing boiler would use to provide the same heat output. Where condensing boilers are described as being up to eighty percent efficient, gas-fired heat pumps offer an efficiency factor of around one hundred and forty percent. The cost savings in energy consumption are therefore quite significant and it is hoped that the installation of a gas-fired heat pump will pay for itself within five years.

Even though the performance of gas-fired heat pumps is affected by changes in the external ambient temperature, they can still operate quite effectively at sub-zero temperatures.

It is possible to reverse the process to supply a highly efficient cooling system that can be operated during the hotter months of summer.

Although they can be used to extract heat from a ground source and other environmental heat retaining mediums, gas fired heat pumps are particularly suited to collecting heat from the air. As such, they are designed to be sited externally. The new versions starting to enter the domestic market can be freestanding or attached to the building.

It is hoped that eventually they will provide a suitable replacement for condensing boilers that have come to the end of their working life.

Because of the high heat output and the method of operation, gas fired heat pumps can be plumbed into any already installed heating system. It is likely that they will eventually form part of the ongoing process of the retrofitting of technological advances in the manufacture of water heating and control systems into existing installations.

Gas fired heat pumps are still in the process of further development. It is likely that as time progresses, purchase and installation costs will reduce and heat transfer efficiency will increase. However, gas-fired heat pumps are likely to rapidly become the accepted replacement for condensing boilers.




Combi Boiler Pressure Checks

Gas combination condensing boilers, better known as combi boilers, are highly efficient water heaters. They are compact fuel misers, designed and installed to extract the maximum heat from their fuel source.

Unlike their open vented counterparts, combi’s are designed to run a pressurised hot water central heating system that eliminates the need for feed and expansion tanks. This attribute is most advantageous in a property where available space is limited.

Like any sophisticated appliance, combi boilers respond well to good and regular attention. Annual maintenance and servicing by suitably qualified engineers will help to keep a combi in good operating condition. This provides peace of mind for a homeowner in knowing that the boiler is performing in line with requirements and unlikely to break down in the depths of winter.

However, combi boilers require another simple check that can be carried out by the homeowner. Checking that the combi boiler operating pressure is correct and undertaking the necessary operations to maintain it is a relatively easy task.

A combi boiler pressure check should be carried out once a month on a correctly functioning boiler.

The pressure within the central heating system is registered on an analogue dial or digital display panel. In most modern combi boilers, the dial or display is located on the boiler. This can be either on the front, sometimes beneath a protective flap, or at the base, but not always immediately visible due to the boiler cover. It is not usually necessary to remove the boiler cover to observe the pressure register.

Very occasionally, the pressure registering display device is located separately from the boiler but is generally in the vicinity of it.

To locate and correctly identify the pressure gauge, the homeowner should refer to the combi boiler instruction manual.

Having located the pressure-registering device the current pressure within the system can be ascertained. A normal pressure range will be between 1 and 2 bar. On an analogue gauge, a black needle will indicate the pressure on the numbered dial face. On some models, the acceptable cold working pressure area will appear as a green coloured fraction on the dial face. Occasionally a further red needle will be present. This is adjustable and can be set to indicate the optimum operating position that conforms to the manufacturer’s recommendations.

As operating pressures may vary between manufacturers and boiler models, the manufacturer’s instruction manual should be consulted to establish the correct pressure ranges.

Where a boiler appears to be operating at a lower pressure than recommended, the system will require pressurising.

To pressurise a combi boiler central heating system, a filling loop is usually provided as part of the installation. The loop consists of a short length of flexible metal or plastic tubing. This will have screw fittings at each end. There should also be valves at either end of the loop. These may be of a lever or screwdriver operated type.

Before commencing to pressurise the system, the gas burner on the boiler should be turned off. It is probably easier to work on a cold boiler and central heating system.

With the loop valves in the closed position, one end of the loop must be screwed onto cold-water input branch feed beneath the boiler. The other end should be attached to the cold-water branch from the mains cold feed. Both these feed points will have flow control valves.

With the loop securely attached, the loop valves can be opened. The mains water branch feed valve can also be opened. To commence pressurisation, the cold mains inlet feed valve should be carefully operated. The sound of water entering the boiler should be heard.

Whilst observing the boiler pressure indicator gauge or digital display, the valve should be kept open until the correct pressure has been achieved and registers on the display.

Once the correct pressure has been reached, the valves on the loop and the two feed pipes should be turned off.

The filling loop can then be disconnected and the boiler operated. It is not good practice to leave a filling loop permanently attached to a combi boiler.

On some combi boilers, a filling loop is not required and the boiler has an internal pressurising system. This is operated by a dedicated key that has to be inserted into the base of the boiler. The key locks into an internal pipework mechanism and turning it operates the pressurising system. The pressure gauge must still be monitored. When the correct pressure is achieved, the key can be unlocked and removed.

On some boilers, instructions on pressurising are displayed on the boiler. However, the best practice is to consult the operator’s manual where detailed instructions for pressurising the specific boiler model will be found.

After pressurising, the central heating radiators may require bleeding. After bleeding the radiators, the pressure gauge should be re-checked, as it is often necessary to add a little more pressure into the system.

If, when attempting to pressurise a combi, the pressure cannot be raised, immediately check the entire system for evidence of a possible leak. Another cause of not being able to pressurise the system is an inadequate mains water pressure. This may be caused by maintenance operations or burst pipes on the mains network. Often, when the mains pressure is low, the boiler will not function by design.

Where a combi boiler loses pressure frequently, a fault may lie within the central heating system or the boiler itself. If, after checking the system for leaks and checking the boiler’s pressure release valve for faulty operation no problems are evident, it may be necessary to employ the services of a qualified engineer.

Significant problems can often occur when a combi boiler is installed to replace a conventional boiler. The pressure produced by a combi boiler may cause problems in an older central heating system. It is important to have the old system professionally pressure checked prior to installing a combi boiler.

When properly maintained and cared for, a combi boiler will continue to work efficiently and reliably for many years.