Tag Archives: boilers

Baxi Potterton Myson Job Opportunities

Paul Clancy, Managing Director, Baxi Potterton Myson

Paul Clancy, Managing Director, Baxi Potterton Myson

Commercial Sales Advisor — Baxi Potterton Myson                                                       Baxi Potterton Myson is looking to appoint a Commercial Sales Order Processing Advisor to promote the sales of BPM products and warranty schemes, offer after sales/technical support, and trade awareness via marketing and other related sales/trade events. The Commercial Sales Order Processing Advisor will support the field-based sales team across the entire BPM product range covering all brands and solutions offered.

Key responsibilities include:-

— Sales order processing

— Promote BPM product ranges;

— Establish new customer relations while reinforcing existing trading partnerships;

— Provide technical support and after-saes service

— Promote the sale of BPM warranties;

Attractive Salary plus a performance bonus, contributory pension and 21 days annual leave outside of bank holidays.

Business Services Support — Baxi Potterton Myson                                                                                   Baxi Potterton Myson Ireland is looking to appoint a Business Services Support Advisor. This is a new position created to ensure the engineer workflow is managed efficiently.

The Business Services Support Advisor is a varied role, requiring an organised and confident mindset, and involving a customer interactive role.

Key responsibilities include:-

— Allocation of jobs to the engineering division;

— Identifying chargeable and none-chargeable events and liaising accordingly with customers;

— Managing commissioning work;

— Order processing and account queries;

— Assisting with the purchasing and sourcing of spares/parts;

— Assisting with stock level monitoring;

— Managing training courses.

Attractive Salary plus a performance bonus, contributory pension and 21 days annual leave outside of bank holidays.

To apply for either role email your CV to vacancies@baxi.co.uk

Tony Cusack Joins Eurofluid

Tony Cusack

Tony Cusack

Tony Cusack, who is well-known and highly-respected within the building services sector, has joined Eurofluid Handling Systems Ltd in the newly-created role of Business Development Consultant. Tony has over 40 years experience in the pump industry and held many senior roles down through the years, culminating in the role of managing director of a leading-brand international pump manufacturer.

Tony now has responsibility for the development of strategies to increase sales over 2015 and beyond, both within the existing Eurofluid product ranges and also with regard to the launch of new, exciting and innovative product ranges.

His vast experience will be invaluable in expanding the already-successful Eurofluid business and he is optimistic that the growth pattern now being experienced by the company can be developed to take the company to the next level.

Eurofluid Handling Systems Ltd is the leading independent supplier of complete plant room solutions which would include Smedegaard/KSB pumps; Europak water boosting systems; Europak pressurisation systems; ACV direct-fired water heaters; Lapesa’ stainless steel calorifiers; Flamco air/dirt separators and vacuum degassers; Condensing boilers c/w stainless steel heat exchangers and delivering one of the industry’s best space-saving footprint. This includes single boiler units up to, and including, 1.2 mW in size.

 

TGD-030 Guidance Document Changes — Implications of revised guidelines on boiler selection (Part 2 of 2)

David Doherty, Vice-Chairman CIBSE Ireland and Projects Manager, Hevac

David Doherty, Vice-Chairman CIBSE Ireland and Projects Manager, Hevac

Section 11.2 of the revised changes to Technical Guidance Document TGD-030 covers boiler selection specification. The revised issue now reads: “where natural gas supply is available, suitably-sized aluminium or stainless steel modulating boilers shall be provided”. The key wording here is aluminium. This change now allows for more competitive and efficient condensing boiler plant to be considered.

Aluminium has a number of favourable characteristics. The alloy is perfect for casting of boiler bodies with complex shapes which allow increased surface areas for maximum heat transfer with low water volumes.

As aluminium conducts heat better, in choosing this material, we can significantly reduce the exchange surfaces to achieve the same output transmission to the heating circuit with a smaller exchanger. At an equivalent output, aluminium heating bodies are therefore significantly more compact. Aluminium is three times lighter than stainless or copper.

The compactness of aluminium exchangers – combined with its excellent thermal properties – allows mechanical contractors to take advantage of significant weight reductions with the same amount of power.

Aluminium silicium is extremely flexible, which allows considerable temperature differences (up to 30k) between the boiler flow-and-return. There is no risk of metal fatigue caused by repeated thermal shocks throughout the heating season which can lead to breakage of components.

The thermal conductivity of aluminium (99.9% purity) is 237 (W.M-1.K-1 @ 20°C) while stainless is 46 (W.M-1.K-1 @ 20°C). This represents a greater heat transfer by five times that of stainless steel. This in turn allows for smaller exchangers and boiler sizes. The density of steel is more and therefore weighs more. This can become an issue on large boiler plant for installation and building structural loads.

The construction of stainless steel heating bodies involves weld assemblies, folds and pressed parts which are susceptible to the constraints relating to the operation of the boiler. The changes in temperature relating to the operation of the boiler are the root cause of stress in materials. These manufacturer welds and lock seams can be a weakness in the exchanger assembly. An aluminium boiler does not incorporate any folds or welds.

Alloy resistance to acidic conditions is critical, especially during condensing mode. Aluminium can resist these corrosive conditions due to its ability to become passive. On contact with water or oxygen, a non-porous protective layer of aluminium oxide is formed naturally. This is alumina, or the passive layer. It is this layer that makes the alloy suitable to the condensing conditions of modern boilers.

As the boiler is not susceptible to thermal shocks, the boiler can have low return temperatures. thus allowing it to condense and therefore recover heat. During condensing operation, the condensate run-off flows down over the heat exchanger. This acts as a method of self-cleaning by preventing the accumulation of any residues and non-combustible materials on the exchanger and, in effect, continuously washes the exchanger.

In order for any heating system to operate properly clean neutral water is ideal. The addition of an inhibitor to the system at commissioning stage will keep any remaining grit in suspension and prolong the life of the system and the boiler. Proper system flushing to rid the pipes of filings, dirt or grit is recommended.

Water quality parameters are measured by pH, hardness, conductivity and chloride levels. These levels will vary geographically from county to county. The table shows why it is necessary to include a protective inhibitor. Steel and cast iron corrode easily on contact with water, as the pH of the water network is not naturally compatible with these alloys. Conversely, aluminium presents good resistance to neutral or even acidic pH, and is one of the metals most resistant to corrosion due to its broad tolerance range.

In conclusion, aluminium silicium boilers have a number of positive characteristics – including corrosionresistance, longevity, ductility and conductivity – and these are prime considerations when specifying or making boiler selections.

Technical Guidance Document TGD-030 — update and changes summary (Part 1 of two articles)

David Doherty, Vice-Chairman CIBSE Ireland and Projects Manager, Hevac

David Doherty, Vice-Chairman CIBSE Ireland and Projects Manager, Hevac

TGD-030 Mechanical and Electrical Building Services Engineering Guidelines covers primary and post-primary schools and its scope is to offer better guidance to school authorities, and to aid mechanical/electrical engineers in design. TGD – 030 should be of interest to building services consultants, contractors and suppliers involved in schools works and, in particular, the current summer works scheme underway at schools throughout the country.

The document covers various design features including natural ventilation, boiler plant and rainwater harvesting. This publication of the latest revision follows consultation and communication between the department and building professionals, designers and suppliers/manufacturers. It has been widely welcomed and endeavors to future-proof the

M&E services provided in schools. Key changes include:

Daylight Distribution — Average daylight factor for rooms remains at a minimum of 4.5%. The document notes that: “Higher levels just lead to unnecessary heat gains and losses”;

Ventilation — Natural ventilation is to be considered where possible via permanent wall vents and windows. The guideline notes that: “good quality ventilation is critical to the functioning of a teaching space”. The latest revision highlights thermal comfort levels. The maximum time a room can exceed 25°C is 51.85 hours. However, this is an absolute maximum and design team members should endeavour to maximise the thermal comfort potential;

Blinds — The specification on blinds now includes light transmission values 9 – 12%; solar absorption 17-20%; openness factor 3 – 5%, depending on elevation. All blinds to be light and identical in  colour. Instructions on operation to be included to try reduce energy costs;

Access — The document draws attention to Part M Access & Use. It highlights sensible and thought-out locations for light switches, sockets and lift equipment. This is something every project tries to achieve through coordination and layout drawings;

Boiler House — Maximum plant room sizes are now detailed and linked to number of classrooms;

Boilers — Where natural gas supply is available, suitably-sized aluminum or stainless steel modulating boilers shall be provided. This allows for a more efficient selection, and the inclusion of modulating allows for better turn-down ratios on boilers. Weather compensation and three-port mixing valve arrangement with an outside sensor brings the specification up to date with modern wall-hung and floor-standing boilers;

Radiators — Radiator metal thickness, minimum 1.5mm. No fan assisted radiators allowed;

Controls — Clear instructions on heating controls now required;

Water Supply — Test point in boiler house now to be allowed for water sampling, in addition to a dosing point for commissioning and disinfection. The document highlights the requirement for drinking points as per TGD002 and mains water should not be piped to wash hand basins;

Rain Water Harvesting — A new sizing guide is now included for underground storage tanks. No mains water connection should be made to a tank. Anti-legionella requirements are highlighted along with rainwater tap labelling;

Water Services — Attention is drawn to national and international standards that minimise the risk of legionella;

Water Tank Ventilation — Cold water tanks are to be stored below 20°C. Consideration is drawn to stagnate water and calls on both architects and building services engineers to ensure risk of legionella is minimised. If passive ventilation is needed a duct to outside can be considered;

Sanitary Ventilation — All sanitary facilities, including en-suite classroom toilets, to be provided with background ventilation. Shower areas 15 l/s per shower. Toilets 6l/s per WC. En-suite bathrooms must contain an external window, in addition to a mechanical fan, with run-on timer controlled by light switch. Floor grilles and door transfer grilles should not be used with undercut doors and high level transfer grilles are preferred. All systems to be tested and commissioned in accordance with CIBSE commissioning codes;

Dampers — All dampers to shut off when fan not in use. A non-return damper to be provided on ducts of 150mm or less. Motorised dampers are required on larger duct sizes;

Power Distribution — Residual current breaker and overloads need to allow for heavyduty floor cleaning equipment. Lightning protection to be considered. Electronic surge protection required on incoming mains supply at mains switchboard;

Lighting — LED type fittings are to be considered for external, car park and security lighting. Payback of 10 years is required. CCTV compatibility is required. On internal spaces, LEDs can only be used in corridor and toilet areas. Elsewhere, lighting power consumption levels of 2.5w/m2 per 100 lux shall be the maximum in all areas. Lighting detectors, plus operation instructions, also required.

Also, corridor lighting zones need to consider daylight influences and have local PIR controls alongside local switches. The document looks for commissioning and a re-visit 12 months after handover to ensure levels maintained;

Emergency Lighting — Installations are to comply with IS3217:Dec.2013. Economical solutions are to be considered with ceiling-mounted LED fittings rather than inverter driven packs. The DoES takes the view that a classroom is not a large assembly room. A single fitting will comply, allowing 0.5lux at floor level. Siting of lighting to consider routes and location of emergency equipment;

Communications — In public address systems, local volume control required in classrooms with special education needs. Regarding induction loop systems, the loop cable is not to be run in steel conduit or in the floor;

Fire Alarm Systems — Systems to comply with IS3218: Dec.2013. Open protocol type fire alarm systems only shall be provided in schools.

The document concludes by outlining handover documentation and requirements for labelling in the control and operation of the equipment. For further information on all the DoE documentation – and to download the entire file – visit their website: www.education.ie/en/School-Design/ Technical-Guidance-Documents/

Boiler Selection Must Be Done in the Context of the Design of the Overall Heating System

Boiler basics
Most heating boilers don’t boil, they generally produce Low Temperature Hot Water (LTHW) at 80°C. Only steam boilers actually boil the water and they are mainly used in very large industrial sites. Some large multi-building sites operate on medium (MTHW) or even high (HTHW) temperature hot water allowing the designer to minimise the diameter of distribution pipework and hence capital costs. Some heating systems (e.g. underfloor) operate as low as 40°C and these are ideal for condensing boilers.

Space heating boilers are most commonly fuelled (fired) by natural gas but oil is still widely used and, with the drive to reduce carbon emission, biomass boilers are gaining in popularity. EU Directives Directive 92/42/EEC of 21.5.92, which comes under the SAVE programme concerning the promotion of energy efficiency in the Community, determines the efficiency requirements applicable to new hot-water boilers fired by liquid or gaseous fuel with a rated output of no less than 4 kW and no more than 400kW.

New boilers, within the size range 4kW to 400kW sold in the European Union, must operate at, or above, the specified minimum percentages efficiencies as per the Directive while running at full load or part load conditions.  New heating appliances, i.e. boiler combustion chambers (bodies) and burners, are normally marketed as separate items, and must meet the relevant efficiency requirements, when they are assembled together to form a complete boiler. Table 1 indicates the minimum requirements to comply with the Directive.

Table 1

Seasonal and part load efficiencies
The key factors determining the seasonal performance of a boiler is the efficiency of the plant at part load, and the load that the plant experiences in response to the seasonally varying building heating demand. Part-load efficiency refers to the ability of a system to handle part-load energy use and it should be taken into consideration when specifying an mini HVAC system. Here is how you can start installing your own mini split system. Systems generally operate at their peak efficiency when they are working at their maximum capacity and most systems are sized to meet heating conditions that occur only 1% to 2.5% of the time. Because of this, systems are often oversized, rarely operate at full load, and thus do not operate efficiently.

Designing for part load
Proper sizing of a HVAC system can maximise partload efficiency. Selecting the appropriately-sized system requires an understanding of the peak heating load and the system’s load profile.
(1) Determine how often the HVAC system will be running under part-load conditions;
(2) If that will be a frequent occurrence, look for a system that will be efficient for those partload conditions;
(3) Beyond right-sizing equipment, there are system components and modular components that can be selected to improve efficiency. A few examples of these components that can operate efficiently at part-load include variable speed drive controls for pump motors; variable capacity boiler plants, and temperature reset controls for hot water.

In buildings with highly variable loads, which is common in commercial buildings, multiple, modular boilers are an option. Modular systems are more efficient as they permit each boiler to operate around maximum rated load most of the time and reduce standby losses. Other options include condensing boilers, and modulating boilers that can run at partial capacity rather than cycling on and off.

Some engineers design systems with multiple boilers – one can be sized for 75% to 80% of the design load, while another is sized for the part load (30% to 40% of the full load). Operators can then select a unit based on the energy efficiency performance and the heating needs. Careful sequence control is fundamental to this approach.

Benefits include greater energy efficiency, reduced running costs, improved load matching, built-in standby capacity, flexibility in maintenance and allowing the most efficient boilers to take the base load. Overall energy savings of 5-10% are typical.

Gross and net calorific values
There is often confusion about the presentation and use of gross and net calorific values data for heating equipment. In simple terms, the calorific value (CV) is the amount of heat released when a specific amount (weight or volume) of fuel is completely burnt in oxygen. Most commonly used fuels (oil and gas) contain hydrogen and when burnt this hydrogen is converted to water vapour that, when fully cooled, is converted to liquid water.

During the process of converting water vapour to its liquid state a certain amount of heat is released. Condensing boilers recover some of the heat in the water vapour so it is possible to achieve efficiencies greater than 100% net efficiency. This is known as the latent heat of condensation. The possibility exists for the measurement of calorific value to include or to exclude the latent heat of condensation/evaporation, thus there are two values of calorific value for a fuel. The higher value, including the latent heat, is the “gross” CV and the lower value is the “net” CV. See Figure 1.

Figure 1

The two approaches are simply different scales for measuring the same. For product comparisons and sizing boilers, ensure that all the information is based on either gross calorific value or net calorific value — don’t mix the two. Heat output shown on manufacturers’ literature might be based on either gross or net and this can make a significant difference when specifying equipment.

Burner/boiler technology
The objective of a burner is to achieve combustion with the correct mix of fuel and air so that all the fuel is burnt efficiently. There are various types of burner, brief details being as follows:

Atmospheric burners – gas is injected through the burner which entrains the air necessary for combustion. This is the most basic and least efficient approach, and one that the market is moving away from;

Pressure jet burners – a fan forces air into the burner, the fuel (gas or oil) is then mixed in at  the burner nozzle and fired into a combustion chamber. Usually used on larger boilers;

Pre-mixed burners – gas/air is mixed before combustion in a mixing chamber, then forced through a burner and the flame sits on the burner. The main advantage of the pre-mix method is that the combustion air can be controlled very closely to achieve the correct ratio of air and gas mixture at all times. This has the effect of improving combustion efficiency.

High-efficiency boilers – These boilers generally have low water content (and/or low thermal mass) with even greater heat exchange surface and insulation. They achieve around 85% at full load falling slightly to around 80% at 30% part load. The higher part load efficiencies make them particularly suitable for applications with a wide range of loads.

Condensing boilers – These boilers use an additional heat exchanger to extract extra heat by condensing water vapour from the products of combustion. They operate at a minimum efficiency of around 85%, even when not condensing and can achieve efficiencies in the range 85/95% depending upon the system return water temperature. Condensation begins to occur at return water temperatures below 55°C and the lower the return the more efficient the boiler. In underfloor heating systems that operate at 30-40°C they can achieve seasonal efficiencies over 90%

However, the more common approach for standard radiator systems is direct weather compensation to achieve around 88%. Constant temperature 80°C flow systems for fan coil units or air handling units are less appropriate for condensing boilers as payback periods will be less attractive. Condensing boilers provide typical energy savings of 10/20% when replacing existing older plant, resulting in paybacks of between two and five years depending on the installation.

Boiler arrangement and system integration
The first step in achieving an energy efficient heating system is to minimise the demand for heat. The structure and fabric composition of the building will influence the heating strategy and can be designed to minimise heating energy consumption. Before designing a heating system it is essential to ask: ‘Have the demands been minimised?’

There are a few useful rules to follow when designing energy efficient heating systems.
Designers should:
• Select fuels that promote high efficiency, low emissions and minimise running costs;
• Segregate hot water services generation wherever possible;
• Locate plant to minimise distribution system losses;
• Insulate pipework, valves, storage vessels etc effectively;
• Choose efficient primary plant, such as condensing boilers;
• Consider energy recovery, e.g. from air exhaust streams;
• Distribute heat effectively by avoiding excessive pipe lengths and system resistance;
• Use effective controls through good zoning,effective time control and variable flow control where possible;
• Consider de-centralised heating and hot water services generation plant on large sites to reduce standing     losses and improve load matching.

But:
• Avoid over-designing the heating system itself as oversizing can lead to a significant drop in efficiency;
• Ensure that the base load is provided by the most efficient plant;
• Always consider the part load efficiency of the overall system since much of the year will be spent operating at part load; ensure that large central systems do not operate to meet relatively small loads.

Using multiple boilers (modules) in one installation can improve energy efficiency by enabling a good match between boiler output and system demand. During maximum demand on the system in midwinter, all the boilers will be firing. During periods of lower demand (e.g. spring/ autumn) only a proportion of the boilers will be required to supply heat. As the load increases,individual modules are progressively switched on.

The smaller modules spend more time operating at full load compared to a single large boiler, hence, improved seasonal efficiencies. Although this is less pronounced in modern boilers, the principle remains the same, unless the plant has higher efficiency at part load (e.g. condensing boilers).

Figure 2

Figure 2 shows a simple heating system that can be used as a basic building block, which when it includes the following features, can often help to reach a simple energy efficient heating system:
– A pumped boiler primary circuit;
– A common primary circuit pump set (larger boilers);
– A reverse return primary circuit;
– Decouple primary and secondary circuits via a common header;
– Ensure correct set points for boiler sequence controller;
– Set boiler thermostats higher than the boiler sequence controls and ensure that adequate system pressure is available.

Condensing boilers can be more expensive than the standard boiler. To keep capital cost to a minimum while still retaining high efficiencies, it is sensible to mix and match condensing and non-condensing boilers. Other than very low temperature systems, combinations of condensing and non-condensing boilers are normally more cost effective than all condensing boilers. Specifying the lead boiler(s) as condensing, with high efficiency to top-up, optimises capital cost while still keeping overall plant efficiency high. It is common to find that 50/75% condensing plant provides the most economic approach.

Condensing boilers should always be the first choice for ‘lead’ gas boilers in multiple installations. In mixed boiler systems, the additional hydraulic resistance of condensing boilers must be considered when designing boiler circuits and suitable regulating valves used to ensure balanced flows. Always select the most efficient plant. Typical seasonal efficiencies of boiler plant are shown in Table 2.

Table 2

Biomass boilers
Biomass usually refers to the use of logs, wood chip or wood pellets that are converted to heat in purpose-designed boilers. The carbon that is released during their combustion is equivalent to the amount that was absorbed during growth, and so the fuel itself is not only renewable, but also almost carbon-neutral. However, there are some carbon emissions associated with processing the wood into fuel and with its transportation.

There are many forms of biomass. This article will briefly cover wood chips and pellets for use in boilers in commercial developments. The application of wood-fired boilers to building developments, where there is a significant space heating or domestic hot water demand, offers the possibility of considerable reductions in carbon dioxide emissions, generally greater than any other currently available on-site renewable technology.

The design of wood-burning boiler installations is very different, particularly in relation to:
• physical size
• fuel handling and storage
• fuel properties and availability
• emissions and flueing requirements
• operating characteristics
• sizing of plant
• capital costs

Pellet boilers range from domestic models through to units rated at several hundred kilowatts. The level of automation associated with the boiler increases as the boiler capacity rating increases. Wood pellets are relatively easy to handle and have a much higher calorific value than wood chips, and the fuel handling systems required are much simpler.

Wood chip is a cheaper fuel but is difficult to handle and has a lower calorific value. It therefore requires a large fuel store and sophisticated fuel transport system. It is generally true that a wood chip installation can burn pellets but a pellet installation cannot burn wood chip.

Wood pellet
Pellet burning installations generally take advantage of the fact that boilers are fully automatic just like oil and gas boilers. Pellet boilers use advanced microprocessors to control the amount of fuel and air being supplied to the
combustion chamber. This ensures extremely high efficiencies (up to 90%) and ultra-low emissions.

Pellets can also be burned in boilers designed to burn wood chips, which makes the technical upper limit for the application of pellet burning the same as wood chip burning. It would be economic considerations of fuel cost that would indicate a switch to wood chip burning at larger capacities.

Wood chip
Wood chip boilers are generally restricted to stepped moving grate burners which can cope with the handling characteristics and higher ash content of wood chip fuel. There are two types of stoking mechanism, which are applied differently dependant on fuel type used and the boiler capacity; the larger the boiler and the wetter the fuel the greater mechanical intervention required to stoke the boiler.

Boiler and system controls
It is very difficult to separate boilers from the heating system as the two interact to form an overall system efficiency. Equally important is the dynamic nature of heating systems with heat demand changing almost constantly. The most efficient systems have efficient boilers, good heat distribution systems and good controls. The key requirement is to provide heat only when and where it is needed and at the right temperature while minimising boiler cycling.

Use optimum start/stop for time control and weather compensation for temperature control, trimmed by motorised valves or TRVs for zone control. Good sequence control is fundamental to achieving an energy-efficient multiple boiler installation. In particular, careful location of the sensor in a representative part of a constant flow primary circuit is essential for stable control.

All boilers have a boiler control thermostat and a high limit thermostat for safety purposes. In multiple boiler installations these should be set much higher than the sequence controls so that they allow the sequence control to act without interference.

Figure 3

Weather compensation controls reduce the flow temperature in variable temperature circuits as the external temperature increases, see Figure 3. The most common version requires a three-port motorised valve to control water temperature. Weather compensation can provide low return water temperatures in milder weather causing condensing boilers to operate at higher efficiencies.

Optimum start controls are weather dependent time-switches that vary the start-up time in the morning to achieve the building temperature by the start of occupancy. Heat-up times are reduced during milder weather, thus saving around 5/10% of heating energy. Optimum stop controls turn the heating system off early without compromising comfort in milder weather. Figure 4 shows the operation of optimum start controls and the potential energy savings compared with a time-switch.

Figure 4

It is essential to select the most efficient plant and ensure that plant and equipment are not oversized. Plant that is too large will operate further down the part load curve and hence at lower efficiencies unless it is condensing. Where possible, segregate domestic hot water from space heating in order to avoid poor summertime efficiencies. Plant sized to meet space heating and hot water will effectively be far too large for small summer hot water demands and this could reduce seasonal efficiency significantly.

Even a well-designed system can perform badly with poor controls. Conversely, you can’t fix a poor heating design by just adding controls. The boilers, heating distribution and controls have to be seen as one overall system. Regularly carrying out good boiler maintenance is essential to ensure continual high efficiencies. This includes cleaning and setting up the burner, cleaning the heat exchanger to ensure good heat transfer, and setting the boiler controls correctly. ■

References
• Building control systems CIBSE Guide H
• Energy Efficiency in Buildings – CIBSE Guide F

The Heat Beneath Your Feet

Enda Gilroy

In recent years, underfloor heating has become increasingly popular. This is due to the fact that underfloor heating provides a range of opportunities not offered by traditional heating methods, both in residential and commercial buildings. However, underfloor heating also offers some challenges and, in order to make the very most of the opportunities, it is important to choose the right solutions.

Why choose underfloor heating? — There are many areas in the commercial sector where insulation under the floor can be incorporated to benefit potential clients, both in terms of comfort and energy reduction. Money matters now more than ever before, and if an engineer can effectively demonstrate to the client that there is the potential to reduce operating costs and provide increased levels of comfort by incorporating lower energy sources, then underfloor heating has clear benefits.

Some of these benefits include:

– Underfloor heating provides comfortable heating as your feet are kept warm while your head is kept slightly cooler;

– There is much focus today on the indoor climate where increasing numbers of people are plagued by asthma and allergic problems. Due to the large heating surface associated with underfloor heating, less air is mixed and therefore less dust occurs in the room compared to a conventional radiator system with its convection currents of air;

– The room temperature can be lowered 1-2°C which can result in energy savings of 6-12%;

– Low surface temperatures which eliminate contact hazards;

– Long life span.

There are some circumstances where underfloor heating is not suitable and a more conventional form of heating may be more appropriate. This can be due to client’s requirements or perceptions, structural constraints or the flexibility of the space.

Some of the disadvantages associated with underfloor heating are:

– Generally it has a slower response time (in solid floor applications only) compared to radiators;

– Incompatible with certain floor coverings;

– Floor penetrations should be avoided or carefully planned;

– Difficult to change pipe routes once installed.

Applications and design parameters

The principal characteristics of underfloor heating include energy efficiency, economy and excellent thermal comfort. It is an ideal choice for most, but not all applications.

Suitable

Buildings or areas that are used very used continually or frequently; Buildings ore areas with relatively low heat loss; All ceiling heights including atria; Use with all heat sources.

Not Suitable

Buildings or areas that are used very intermittently or infrequently; Buildings or areas with high heat losses, particularly when due to high ventilation rates; Buildings where unpredictable re-zoning may occur; Areas where the floor is largely obscured by permanent fixtures and socket weld fittings are not suitable for underfloor heating.

Room temperatures

The temperature experienced in a room is the result of two different factors, namely the air temperature and the ambient radiation, i.e. from the heated elements in the room. It can be an advantage in many ways that heat radiation constitutes a relatively high part of the “overall” temperature, or the operative temperature as it is also called.

Underfloor heating is not purely a radiant form of heating, typical emitted proportions are 70% radiation and 30% convection. If a large part of the operative temperature is made up of the air temperature, it means that there will be a high convection or mixing of air in the room. If there is high mixing, air is whirled around which leads to higher dust content in the air and therefore a poorer air quality.

Where convection is a high proportion of the operative temperature, the frequent opening of doors or windows can have a negative impact on occupant comfort. For this reason underfloor is particularly suited to foyers or atriums where the proportion of the operative temperature is primarily radiation and is less effected by the opening of doors and windows.

The way convection/radiation occurs with radiators and floor heating respectively can be seen in Figure A. As can be seen, with radiator systems the air temperature or convection makes up approximately 70% of the operative temperature. This is also logical if you think about how a radiator has quite a small surface from which to transfer heat to the whole room.

Figure A. Left – Radiators: 70% convection/ 30% radiation. Right – Uf Heating: 30% Convetion/70% radiation

Conversely, floor heating supplies heat through a very large surface evenly distributed in the room, which means that the ratio is just the reverse with 70 % of the operative temperature being added by radiation.

Floor temperature

The temperature of the floor surface must be sufficient to provide the required heat transfer into the space, but not be so high as to cause discomfort to occupants. Generally in areas where occupants are seated there should be a maximum of 9°C between floor surface temperature and room temperature. This equates to a maximum surface temperature of 29°C in normal occupied areas and 33°C in changing/shower areas with a room temperature of 24°C. In areas where people would not normally be seated such as atria/foyers or areas with high glazing levels, the maximum floor surface temperature can be increased to 15°C above room conditions.

Occupant comfort

In practice, it is not possible to maintain the same temperature everywhere in a room. It is recommended that a difference of approximately 2°C between floor and head height should be maintained. This is because most people want to have warm feet while keeping “a cool head”. But the difference in temperature should not exceed about 3°C as the body will become “confused” and comfort is reduced.

Characteristics and key elements

The rate of heat output from underfloor heating is determined by the following factors:

— Mean water temperature circulating through the floor piping;

— Temperature of the space;

— Spacing and diameter of pipework;

— Thermal resistance of floor coverings;

— Thermal resistance of insulation/flooring under the pipework.

The mean water temperature and pipework spacing can be varied to provide the required design output. This can be used to overcome issues such as high heat loss, floor covering with high thermal resistance or restricted emitter area. The heat output is a function of the surface area and the mean water temperature. Given that the size of the floor area, is so large the mean water temperature can be much lower than that commonly-used in radiators while still providing the same output.

The following describes the major elements of underfloor heating systems:

Energy source

Underfloor heating can utilise a wide range of energy sources. Unlike conventional heating systems that require hot water at temperatures up to 80°C, underfloor heating is effective at flow temperatures of 45°C. It is particularly suited to condensing boilers due to the low return water temperatures. The boiler should be fully condensing under all operating conditions, with the exception of when domestic hot water generation is required. Some of the sources of providing low grade heat and low carbon emissions that are suited to underfloor heating include condensing boilers; biomass boilers; various forms of heat pumps and solar panels.

Heat pumps can take various forms, of which the most common types are, ground-source, water-source and airsource heat pumps. These typically have a Coefficient of Performance (CoP) of 3.5 to 4.0.

Solar panels may also be used as themain heat source, but they are be unlikely to be cost effective. They can, however, be used in conjunction with a conventional heating system or heat pump with the aim of reducing the load imposed on the main heat generator.

Circulation pumps

Ideally, a single pump should be used to circulate water to the manifolds and through the pipework, though some systems may incorporate a secondary pump and mixing valve attached to the manifold. Pump energy consumption should be minimised by avoiding excessive pressure drops in the distribution system and employing variable speed pumps. All pumps selected must comply with the European ErP Directive EC 641 for glandless pumps, which comes into effect in 2013.

Manifolds

The manifolds take the low temperature hot water from the heat source and distribute it through the underfloor heating circuits. There are separate manifolds for both supply and return and they incorporate electric control valves and balancing valves. Depending on the size of the project and the number of circuits, it is not uncommon to have a number of manifolds located throughout the building.

Underfloor heating pipe

There are generally three main types of material associated with underfloor heating:

(1) Cross-linked high density polyethylene (PE-X) to BS EN 15875-2 : 2003;

(2) Polybutylene (PB) to BS EN ISO 15876-2 : 2003;

(3) Aluminium/plastic multilayer composite pipe to DIN 4726 : 2000.

All plastic heating pipes should incorporate an oxygen barrier, and in the case of composite pipes, an aluminium foil incorporated into the pipe provides the oxygen barrier.

Generally, two pipe sizes are available f or underfloor heating, and these can vary slightly depending on the manufacturer, but are commonly 16mm and 21mm in diameter. Increasing the diameter will reduce the flow velocity and pressure drop but also influence the heat output per unit area of the floor (assuming the spacing remains the same).

Insulation

Insulation is a key factor in maximising the output of underfloor heating and particular attention should be applied to this element. BS EN 1264 Part 4 states that the maximum limit to the downward heat loss should not be more than 10% of the heat supplied. This applies even to where the underfloor heating system is installed above another occupied space (see Figure B).

It is very important to provide edge insulation around the floor perimeter where underfloor heating is installed as this prevents thermal bridging. Edge insulation also allows expansion of the floor slab. Factors to be considered when selecting insulation include compression strength, thermal conductivity and moisture resistance. This should be discussed between the building services engineer, the structural engineer and the architect.

System design

The design of an underfloor heating system is no different to any conventional heating design in that the designer must agree the scope of design. All the necessary information on the design requirements has to be gathered from the client/architect etc, and this information is generally greater than with traditional systems, as details of the floor make-up and floor covering need to be considered in the design.

All underfloor heating systems should be designed in conjunction with BS EN 1264 parts 1 to 5, as well as other industry norms including, but not limited to, Irish building regulations and CIBSE guides.

The required surface temperature, and consequently heat output, are achieved by varying the pipe spacing, circulation rates and flow temperature. The depth of the pipe and the thermal response of the structure and covering are usually dictated by other factors.

To achieve the required heat output for each individual area, designers will generally base the required pipe spacing on pre-determined required flow and return water temperatures. Flow temperatures of 45°C and return temperatures of 35°C are commonly used.

Depending on the area in which underfloor heating is to be installed, the spacing requirements can take two approaches. The spacing can be installed to match the required heat output or the pipe can be spaced closer together to increase comfort and/or response time. The latter approach may be beneficial if the floor coverings are unknown or undecided. Obliviously, the closer the pipe spacing the more material will be required and hence there will be an increase in capital cost. The manufacturers of underfloor heating pipework produce a range of tables that cover the selection of pipework and required spacing to achieve the desired output.

Generally in commercial installations the underfloor heating circuit is arranged as a secondary circuit from a primary header. The primary header usually feeds various circuits such as AHU’s, radiators and a calorifier, as illustrated in Figure C.

Figure C

There is an inherent disadvantage with using this arrangement with underfloor heating in that the boiler flow temperature is matched to the highest requirement, which is usually the AHU’s or calorifier. It may be beneficial to consider separating the lower temperature underfloor heating loads by the use of condensing boilers or heat pumps dedicated to the underfloor heating load.

Installation issues

The layout of the pipework is also vital to ensure a cost-effective and efficient design. Too many manifolds can increase the capital cost of the installation, and too few can lead to pipework congestion, local overheating and reduced control.

Generally as a guide the length of a pipework circuit should not be more than 110 metres. Attention to the location of the manifolds needs to be considered, as particular areas of concern are where pipes travel through a corridor to a number of heated zones. This can lead to pipework congestion resulting in uncontrolled and local overheating.

It is also important to consult with the structural engineer with regard to location of all expansion joints. If underfloor heating pipes pass through an expansion joint in a structural slab, then these pipes must be sleeved at least 200mm either side of the expansion joint.

Unlike with conventional heating systems, an underfloor heating specialist is generally employed to install and commission the heating system. This specialist is generally a sub-contractor of the mechanical contractor.

One of the key areas during installation that needs to be strictly enforced, and is not always complied with, is the quarantine of the work areas during the pipe-laying and covering. This is a vital area of concern that can sometimes be overlooked and needs close co-ordination with the project schedule, main contractor and associated sub-contractors. Damage to the underfloor system from personnel or equipment can easily occur where pipes are left exposed.

Controls

There are many ways of controlling underfloor heating systems, from small scale residential to large commercial building management systems. However, the basic components remain the same. The following components are commonly used – electronic room temperature sensors for each zone; outside temperature sensor; electronic mixing valves; two-port zone valves; and master controller.

It is highly recommended that a weather-compensator be incorporated into the underfloor heating design. This raises the floor temperature as the outside air temperature gets colder. This will be beneficial in terms of comfort and also energy efficiency.

Costs

There is a preconception that underfloor heating is inevitably more expensive to install than conventional heating systems. This is not always the case and projects involving over 300sq m of underfloor heating can be cheaper in “install costs” to a comparable conventional heating system. As with all projects, an accurate cost comparison should be conducted which takes account of the whole life costs of the system.

The running costs of underfloor heating can also be very beneficial since, as we discussed earlier, the room air temperature can be reduced by approximately 2°C. This translates into a significant reduction in building heat losses and energy consumption. The type and height of a zone also has big impact on the running cost – rooms with high ceiling or atria can see significant reductions in energy consumption where underfloor heating is incorporated.

Reference: Ambrose Air Inc.