HEATING FACTORS IN THE CHOICE BETWEEN RADIATOR, UNDERFLOOR AND RADIANT PANEL OPTIONS.

Transcription

1 Date; 17 th July 2012 TITLE; HEATING FACTORS IN THE CHOICE BETWEEN RADIATOR, UNDERFLOOR AND RADIANT PANEL OPTIONS. Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 1

2 Index; Section 1 Scope of the thesis Section 2 Requirements of the chosen application Section 3 Determining factors in choice between the selected options for the required application Section 4 Practicalities of each selected option Section 5 Conclusion References Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 2

3 Section 1 Scope of the thesis The aim of the thesis is to present and confirm the design and operating principles involved in each of the methods of heating as listed below, look at the options and determine the best solution for a typical Healthcare premises environment. Radiator Heating Underfloor Heating Radiant Panel Heating The thesis will also show the determining factors of how each method is operated and may be perceived by building users. The thesis will present and consider all of the options in terms of such elemental factors as design, installation, operation, control and performance in use. Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 3

4 Section 2 Requirements for the chosen application Application: Healthcare Patient Ward and associated Treatment Facilities The structure of a building is, generally, a passive element which is provided to separate the occupier from the outside environment. By contrast, building services are dynamic elements incorporated into the structure to; Convert the external environment into one that feels comfortable and secure Connect the users to the external world Provide the tools needed to meet the building occupiers needs In some cases it will not be economically possible for different systems to be installed for each individual space. In these cases, the user must decide between a number of alternatives. Such as; Install a single system capable of coping with the highest level of requirement all of the time Install a single system capable of coping with the highest level of requirement for most of the time Install a single system capable of coping with the average level of requirement and accept that there will be short duration shortfalls Install multiple systems to suit differing requirements in differing spaces The aim of the user and designer should therefore be to provide conditions which are neutral to the majority of people working in that space. To do this it is essential that the specific activities to be undertaken in the space under consideration, together with other factors, are clearly understood. Heat Energy Transfer Definition; Convection Heat travelling along or through a material without appreciable change in position of the material particles. Radiation Heat transfer by electromagnetic waves through space from one material to another. HUMAN PERCEPTION OF HEAT Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 4

5 Section 2 (Continued) Radiator Heating; Low temperature hot water radiator heating systems have a convective component of between 50% and 70% and provide a positive room air temperature gradient. Radiant heat output is around 40%, with the remaining 60% convected heat. Radiator systems comprise pressed steel or cast aluminium emitters and are generally used in naturally ventilated buildings, but can also be found in some types of mechanically ventilated and air conditioned buildings. They are typically located around perimeter walls to off set cold down draughts from glazing and prevent condensation from forming on the glass. Good temperature control is achievable with radiator systems and the use of thermostatic radiator valves can provide good local control. They are cheap and easily controlled with a reasonably quick response. As radiators are generally large and obtrusive, aesthetics can be catered for by incorporating the appearance of the radiator with the surroundings or decorative theme of the building. Unfortunately the connecting pipework may be difficult to conceal local to each radiator and control (TRV) must also be considered an obtrusion or weak point regards user operation and mis setting. Underfloor Heating; Low temperature hot water underfloor heating systems (operating at approximately 43 degrees centigrade) have a high radiant component and comprise a matrix of plastic pipe embedded between a top layer of screed and the floor slab below, the installation also generally incorporates a layer of thermal insulation on top of the floor slab. These systems provide a relatively quick warm up and cool down cycle with no impact on aesthetics of the area served and for the application intended, providing a very safe manner of space heating. Underfloor heating requires no high surface temperature surfaces to be exposed and is ideally suited to areas were occupants may not have robust or outdoor footwear. Also, this type of installation has no impact on the visuals of the room or space heated, other than a local temperature sensor for the relevant zone controller, remote and concealable inlet/outlet manifold, pump and valves. Radiant Panel Radiators; Low temperature hot water radiant panels (Ceiling mounted) have a radiant component of up to 65% and comprise an array of pipe work mounted on a metal panel from which the heat is radiated. They are cheap and easily controlled with a reasonably quick response. As radiant panels are generally large and to operate effectively must be installed over a large area, aesthetics can be catered for by incorporating the appearance of the radiator with the surroundings or decorative theme of the building. Radiant panel radiators are mounted in locations where they will not present a direct source of radiated heat onto the occupants, and in a ceiling mounted application, will be out of reach of all. This type of location also allows greater scope for the distribution and concealment of pipework and controls. In order to qualify as a radiant panel, at least 50 percent of the heat from the panel must be transferred by radiant energy. Whenever two surfaces differ in temperature, both surfaces will work to equalize. Therefore, radiant energy will move through a space and turn to heat when it encounters a cooler surface. This energy allows radiant panels to emit heat in several different directions, depending upon placement. While conventional heating elements use forced air to heat a space, radiant panels will heat what they come into contact with. For this reason, they can be placed in floors, walls, or ceilings in a space of any size. All these options operate as served with low temperature hot water from a variety of potential fuels via a central heat source which can be utilised for other heating requirements of a typical building such as domestic hot water services or ventilation based air heating or conditioning. Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 5

6 Section 2 (Continued) Even with good system design, heating controls can still be ineffective. The reason for this is that many system operators have not received sufficient training on the systems they have to manage. To ensure that consistent and effective training is being undertaken it is important that staff training records are updated and reviewed accordingly. Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 6

7 Section 3 Determining factors in choice between the selected options for the required application Application: Healthcare Patient Ward and associated Treatment Facilities Radiator Heating; Radiators are not best suited to a healthcare environment due to a number of factors ranging from difficulties in the maintenance of cleaning regimes for infection control purposes, issues related to access for maintenance, elements of manual operation in its local control and functionality, coupled with vulnerability to damage by equipment, personnel or the general public/patients. Underfloor Heating; One of the biggest factors in underfloor heating is the cost of installation. Installations may be more energy efficient and save money on energy bills, however if they cost more to install initially, it will be a long payback period before any real savings materialise. Running costs can only really be assessed when the heating system is in use. Estimates suggest that underfloor heating reduces heating costs by around 10 15% when compared with conventional heating methods. Another common issue with underfloor heating is the slower heat up time. A large room could take up to 2 3 hours to heat up, but it is worth remembering, it will also take longer to cool down. Some of the more sophisticated systems also incorporate a setback mode, whereby the water temperature will drop overnight to a lower set point rather than completely cooling, this allows a quicker re heat period when the heating comes back on. Not all systems can completely heat a room, some may only heat the floor or simply not have enough surface area to fully heat the space. This may result in a combination of radiators and underfloor heating terminals, each with associated issues. Underfloor heating is not suitable to be installed directly beneath floor mounted units such as desks, cupboards, beds etc as it will cause disturbance to the operational principles of the system. The layout of underfloor pipework can be designed to avoid any fixed fittings, but there is little scope if in the future, there may be a need to change the layout or application of the room, or change furnishings and fittings. A suitable location requires to be allocated to position the necessary zone manifold assemblies. Radiant Panel Radiators; Panels are particularly suited for use in hospital wards and corridors, school halls, classrooms and offices. In fact anywhere where there is a need for high capacity heating with a lightweight aesthetically pleasing panel. Rooms heated by radiant systems can be 1 2 C lower in temperature than rooms heated by convection systems. Approximately one seventh of the amount of water used in a traditional radiator system is used in a radiant panel system, resulting in a quicker warm up period and smaller heating plant demands. Demands on plant and energy are further reduced by the lower frictional levels experienced by water as it passes through pipework. The surface area that water passes over as it flows through a traditional radiator system is larger, creating drag and requiring higher system water operating pressures. Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 7

8 Section 3 (Continued) Operation Radiator Heating; By drawing cold air across the floor of the space served, heating it by convection and rising upwards towards the ceiling. The distribution of the heating system water is by means of traditional pumped flow and return pipework generally within the ceiling voids of the areas served to individual radiator connections. Underfloor Heating; By the introduction of heating at the lowest level allowing a uniform and undisturbed convection to higher levels. The distribution of the heating system water is by means of traditional pumped flow and return pipework to the zone manifolds before passing into the floor screed pipework. Typical Radiator and Underfloor heat output patterns are illustrated below; Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 8

9 Section 3 (Continued) Operation (Continued) Radiant heat means that the warmth is concentrated where it most needed. Room temperatures higher up in the space are usually around 2 C lower than at floor level. Underfloor heating systems function by circulating the heated water through a series of continuous pipe loops fitted within the floor screed of the space served. The pipework creates a large radiant surface which heats the space from the floor upwards. The room or space to be heated can be a separate zone, varying heat output according to the time of day and location. Uniform heating patterns are achieved even in the largest of rooms or spaces, with no cold spots and no draughts produced by air circulation or infiltration. Radiant Panels; Radiates heat from overhead in the space served, maximising heat distribution and usable floor area without compromising the function of the space. The distribution of the heating system water is by means of traditional pumped flow and return pipework generally within the ceiling voids of the areas served. A typical radiant panel heat output pattern is illustrated below; Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 9

10 Section 3 (Continued) Control Radiator Heating; The typical radiator heating control system will generally consist of manual room mounted radiator thermostatic control valves and a circuit compensating control valve linked to an outside air temperature sensor for the building. Underfloor Heating; The typical underfloor heating control system will generally consist of electronic room temperature controllers for each zone, linked to a master controller unit at the local zone manifold. There may also be inputs from room, outside air and manifold temperature sensors, pump and control valves. Radiant Panel Radiators; The typical radiant panel heating control system will generally consist of manual room mounted radiator thermostatic control valves and a circuit compensating control valve linked to an outside air temperature sensor for the building RADIATOR THERMOSTATIC VALVE SET; UNDERFLOOR HEATING CONTROLS; RADIANT PANEL THERMOSTATIC CONTROLLER; Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 10

11 Section 3 (Continued) Maintenance; The maintenance of the central plant, heating distribution pipework and fittings is very similar for each of the options, however the size and efficiency of the plant may be a factor in the overall selection. Radiator Heating; High terminal maintenance, cleaning of exposed and hidden surfaces, manual local controls (TRV) upkeep. Underfloor Heating: Very low heating terminal maintenance, within the space, with some increased element of zone mechanical plant and electronic controls at the local manifold. Radiant Panel Radiators; Low heating terminal maintenance, largely exposed surface cleaning and manual local controls (TRV) upkeep. Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 11

12 Section 4 Practicalities of each selected option Radiator Heating; This is generally understood to be the most direct and obvious form of space heating, however the installation requires careful positioning and application. Whilst traditional radiators are very common, cheap and readily available for the application being considered they present several problems; 1. Hazard to occupants in respect of high surface temperatures, albeit this can be reduced by incorporation of a bulky Low Surface Temperature casing, further compromising usable space. 2. Limitation of available space due to necessary strategic position required. 3. Vulnerability to impact damage during construction and use. 4. Target of vandalism. 5. Misuse by intention or ignorance in TRV operation over the daily heating cycle. 6. Misunderstanding in respect of operation by way of compensation of external temperature and fabric protection. Underfloor Heating; Warm water is circulated through a network of pipes laid under the floor screed, derived from a boiler or separate heat source, heat is transmitted into the floor surface. The entire area of the floor surface over emits heat into the space, by radiation rather than convection. This creates an even spread of heat from floor to ceiling, and reduces heat loss from the building as less heat is able to escape. Underfloor heating system zone manifolds mix return water from the underfloor heating pipework with flow water from the primary heating system pipework. The heating circuit overall temperature is controlled at a constant temperature and the proportions of flow and return water are varied accordingly. This operation is undertaken by the zone manifold, comprising the mixing valve, a local temperature sensor, generally operating under the dictates of a control strategy governed by the overall building management system. The zone manifolds serve to deal with the individual room or zone heating demands under the dictates of the associated room temperature sensors of each underfloor heating pipework loop emanating from the local zone manifold. Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 12

13 Section 4 (Continued) TYPICAL UNDERFLOOR HEATING ZONE MANIFOLD TYPICAL UNDERFLOOR HEATING PIPEWORK TYPICAL RADIANT PANEL (REAR) & CEILING INSTALLATION TYPICAL WALL MOUNTED RADIATOR Radiant Panels; Heat transfer from radiant panels is predominantly radiant (as opposed to convection or conduction), reducing unwanted air movement in the space. This is advantageous in healthcare environments where there may be specific air movement regimes required for infection control or where dust and air movement is required to be kept to a minimum. Flat panels are easy to clean and reduce the cross infection risk associated with wall mounted radiator systems. Space flexibility is optimised, whilst also reducing the potential for damage and tampering, which in turn reduces maintenance requirements and associated costs. Pipework is confined to the ceiling voids, omitting the requirement for further coordination between trades during installation to allow for pipe drops to perimeter radiators. Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 13

14 Section 4 (Continued) Choices Table: Radiators Underfloor Heating Radiant Panel Radiators Advantages Disadvantages Advantages Disadvantages Advantages Disadvantages Short heat up time and fast response to disturbances and control Low radiant efficiency Efficient low energy input Slow warm up period Suitable temperature and operating profile for comfort Possible overheating of surfaces close to heater Minimal operational problems within the heated space Flexibility limited once installed Minimal operational problems within the heated space Inflexible once installed Lower air temperature required to achieve comfort Flexibility limited once installed Low noise boiler and pump plant can be remote from the heated space High distribution losses Low noise boiler and pump plant can be remote from the heated space Requires particular building thermal characteristics Reduced ventilation heat losses and better energy efficiency User operation/interference Comfort in difficult to heat spaces Greater plant and control requirements Absence of thermal stratification also reducing heat loses Possible overheating of surfaces close to heater Reduced surface contact risk Greater difficulties in installation programming Low surface temperature which eliminates contact hazards Higher surface temperature which increases contact hazards Low risk of damage to emitter in normal use No thermally induced air movement to create draft issues Higher risk of damage to emitter in during construction and normal use Ease of cleaning Flexibility at early stage design to permit fit out development Greatest overall environmental impact on efficiency and materials Low risk of damage to emitter in normal use Issues with cleaning and control of infection in Healthcare premises Noise, little plant in area served, wide range of heat sources Ease of cleaning = Lowest advantages, highest disadvantages = Greater advantages, lower disadvantages = Greatest advantages, lowest disadvantages Therefore Based on suitability to intended application, Radiant panels win on safety, comfort and flexibility deciding factors Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. P age 14

15 Section 5 Conclusion Radiator Heating; Radiator installations would be the least expensive option, but may not be appropriate due to restrictions of wall space, cleanliness and vulnerability issues particular to the application. Underfloor Heating; Underfloor installations would be the most expensive due to overall integrated costs (screed and finish issues) and not altogether practical due to construction, installation programming and coordination issues. Radiant Panel Radiators; Low maintenance, high user comfort and operation efficiencies make this option best suited to a healthcare application of this type. TYPICAL CEILING MOUNTED RADIANT PANEL HEATING APPLICATION IN A HEALTHCARE FACILITY. Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 15

16 References Choosing Building Services, A Practical Guide to System Selection by John Langmaid, BSRIA BG 9/2004 Underfloor Heating and Cooling, BSRIA BG 4/2011 Energy Efficiency in Buildings, CIBSE Guide F An Illustrated Guide to Building Services, Comfort Systems by Tom de Saulles, 27/99 Myson Floortec Underfloor Heating, Brochure & Technical Guide July 2011 Zender webpage Oikos webpage Greenspec webpage Heating factors in the choice between Radiator, Underfloor and Radiant Panel options. Page 16