Introduction
Perceived comfort of heating within a building – be that in a home, an office, or any other facility-depends on many different factors, including physical, physiological, and psychological ones.
The vital physiological aspects include both the metabolism arising from physical & mental activity of the bodies in a room and the ‘innate’ metabolism of those bodies themselves – for example, breathing, digesting, even the act of shivering!
The type & level of clothing being worn is a crucial factor, being a balance between ensuring enough air-entrapment within the layers and the breathability of those layers to keep heat in and let humidity (sweat)out. When the heating system involves transferring warmth by the convection movement of the heated air itself or by fan circulation, the prospects of getting a consensus view on comfort seems impossible. In most cases, the control of the thermostat setting usually involves compromising upwards! This, however, now ‘flies in the face’ of current advice, that to achieve a carbon-neutral Britain by 2050, thermostats need to be set at lower levels than has recently been the case. National GridESO recently cited that a 1oC reduction in thermostat setting will deliver a 13% reduction in energy consumption.
But should the temperature in a room always be the determinant of how comfortable occupants feel? This is certainly the stance taken by BRE when addressing the UK’s Standard Assessment Procedure (SAP10.2). But is this correct?
Those who enjoy winter skiing or climbing will know the joy of being in a sheltered spot on a mountain top, with ambient temperatures near to or even at freezing, yet being blissfully comfortable wearing a tee-shirt in the cloudless Alpine air! Why is that? The sun’s radiant energy isn’t heating the attitude that it passes through – the electro-magnetic radiant energy waves simply pass straight through the atmosphere, only converting to heat energy when they physically ‘hit’ a solid body – including a human body.Ironically, the more bare flesh that is exposed, the warmer one feels! This is due to the high “emissivity” factor of skin (~0.97), being near an ideal blackbody radiator. This explains why IR heat must be assessed differently from systems that heat the air itself.
IR heating within a building has the same impact as theAlpine skier effect, so if sufficient IR energy is impacting directly with occupants of a room, they too enjoy that same blissful comfort as the skiers feel. The outcome? They can experience comfort, even if the ambient room temperature is very appreciably below 20-23oC, which is the level at which we have come to expect the heating thermostat to be set, but which now isa crucial contributor to global warming!
This effect isn’t new – psychology and maths have been intensively researched for nigh-on 100 years, as we shall touch on in this case study.
However, the development of new IR heating emitters, capable of giving almost instantaneous comfort heating, using (potentially) zero-carbon energy, has re-surfaced the issue of how such new products should be handled& ‘energy scored’ under the UK’sSAP10.2 procedure, which still predicates on using room temperatures achieved as being the critical factor.
2DHeat Ltd IR Panels
The novel IR panels used in this case study are unique, being available only from 2DHeat Limited. The electrical resistor coating technology used for our patent-pending technology was developed in-house by 2DHeat themselves. These coatings operate at much higher watt density levels than available from alternative IR panel heaters or embedded IR ‘meshes’, which means that our panels are not only very much smaller in size (& also lighter in weight) than competitors’ offerings, but heat-up much more quickly, making heating-on-demand feasibility.Furthermore, these panels are available in a full range of power ratings (from300W-1800W), each being only 600 x 600mms in size and 20mm depth – very discreet and unobtrusive.
The directly heated radiant heating surface is ceramic coated steel, with a relatively high emissivity factor of 0.8-0.9. This robust coating is hygienic and easily cleaned. Being high watt-density resistors, they emit high IR energy levels directly from the switch-on, reaching full operating radiance (and panel operating temperature) within a low number of minutes, as detailed below. We call this “heating-on-demand”– i.e. only heating those rooms actually in use or required imminently. This is entirely in line with the philosophy of the Eco-Design (Lot 20 Part L) Building Regulations. In contrast, typical convection heating systems (including water-filled radiator systems) can typically take 15- 20 minutes to achieve their designed operating levels(typically 65oC for water-filled radiators) and then to ‘convect’ that energy from the radiator into the room itself, warming the air itself in that process, but taking a further 10-20 minutes in the process.
The heating trials
The following trials were conducted in 2DHeat’s offices during mid-late May 2021 under the following conditions:
- Unseasonably cool and wet period in the North West of England
- The building is a ~1950/60’s’s industrial unit, of 12” brick external walls, breeze block internal walls with 20ft apex roofing with northern light windows.
- Offices and laboratories are of timber & plaster board walls with suspended ceilings incorporating 6” rock-wool lagging.
- All glazing (looking onto the internal workshop area only) are recently installed 20mm double-glazed units.
- No External Windows
- An overall office U value of ~2.3-2.5 is estimated; i.e. not very efficient by modern building standards
- L-shaped office in which the trial took place measures 72m3 overall, with a lagged suspended ceiling (2.37m height). Solid (external) walls are of plastered 12” brick with internal(partition) wall of low-density breeze-block construction; two internal walls(into the main – unheated – workshop area) are of (lagged) timber batten/plaster-board construction.
- For convenience, a single IR panel heater (575W) was mounted on a flip chart board holder, at an approx 10o inclined angle) with the centre of the panel some 1,600mm above the solid floor construction). This panel was placed 2,650mm from the test-occupant, and3,000mm from the matt painted partition wall behind that occupant, where heating response times were recorded. (See layout diagram below).
- East-facing brick wall - chest high (Open-Sun) - Outdoor
- East-facing brick wall - chest high (Shade) - Outdoor
- Internal wall in lobby area - chest high
- On desk top (wooden)
- On rear wall (head height when seated)
- Solid floor temperature (Full shade) - at feet of test person
- Wall temperature (shaded by screen)
Run 1
Friday 21/05/2021 at 14:00hrs
Weather : grey/ wet/ heavy rain showers/calm wind.
Note that 2 people had occupied the office test area since08:00 hrs, each operating laptop computers, but with no other source of room heating prior to 14:00hrs, when the 575W IR panel heater was switched on.
Run 2
Monday 24/05/2021 @ 08:45hrs
Weather: full sun/ clouding over mid-morning; occasional light showers in the afternoon
NOTE 1: ASHRAE rating of thermal comfort: denotes a 7 point scale initially developed by the American Society of Heating, Refrigeration & Air-conditioningEngineers in the 1930s.
In his very extensive Review of Thermal Comfort Factors (2nd edition 2007 - ISBN 0 86776 729 4,)Steven V Szokolay (past Head of Dept of Architecture & Director ofArchitectural Science Unit at the University of Queensland) reviews (into among other things, long history of subjective assessment of heat comfort factors and the quantification of the same. He identifies the 7 point ASHRAE scale and includes the following graphic, developed by D.S.Woolard in a 1981 study in the Solomon Islands. Since that time, the 7-point scale has been re-written as a -3 through to +3 scale, covering cold through to hot, with the zero point representing ‘balanced comfort’. This is the annotation scale used in the above tables.
It should be recalled that range of body temperatures between hyperventilation and over-heating is very narrow. Hence this -3 through to +3 scale should be interpreted across that same limited range – therefore, on the +ve side, an assessed rating of +2 represents a very significant‘ discomfort’ factor. A more graphic set of descriptive terms could well be as follows:
+3 = much too warm
+2 = too warm
+1 = comfortably warm
0 = comfortable
-1 = comfortably cool
-2 = too cool
-3 = much too cool
Results
From the office trials covered above, it can be seen that bodily comfort to IR heating (i.e. an ASHRAE assessment of 0 to +1) can be equated to a physical room temperature some 3.0-3.5oC lower than current conventionally expected thermostat settings for classical convection heating systems. Interestingly, this conclusion is not dissimilar to extensive studies carried out in Germany by EIHAP, an association of IR panel manufacturers.Their 2016 report (http://eihap.com/2016/06/09/the-future-is-electric/)included their finding of up to 32% better energy efficiency for IR panels versus all convection heating sources and with a stated comfort level of some 2-3oC lower room temperature. This finding was based upon their compilation of studies over a number of years. It included many different housing types, in other locations, with a wide range of occupancy types &numbers.
Some key conclusions from our case study:
- A ‘comfortable’ level (ASHRAE scale 0/ +0.5) of heating in a cool room (15.1o-15.2oC) is quickly felt within 3-6minutes from switch-on using our new high-watts-density IR panel heaters..
- A ‘comfortably warm’ (ASHRAE scale +1) level of heating exists whilst the temperature of the room is still only between 15.2oC and 18.3oC – i.e. well below the “popular” thermostat set level of20o-21oC.
- A ‘too warm’ comfort level (ASHRAE scale +1.5) and very uncomfortably warm’ (ASHRAE scale +2.0) begins to be experienced once the temperature exceeds ~19oC.
- By the time the temperature exceeded 20.0oC, switching off the panel heater was necessary to restore an optimal comfort factor; further heat input was unnecessary for an additional 35 min duration.
- It is to be recalled that this study involved a single575W panel heater in a ~72m3 room, albeit focused onto a particular workstation within that room. Conventional practice for this size of space, with a relatively poor estimated ‘U’ value of 2.3-2.5, albeit it ‘relatively well sheltered from winds, etc. by its location within a larger factory unit, would require around2.0-2.5kW of input energy to provide a ‘good comfort’ heating. Thus, it could be concluded that two such 575W heaters, ceiling mounted and working independently, could satisfactorily provide the heating needs of all the workstations in the ~72m3 room.
Other Case Studies in this series:
Case Study 2(see) details the extensive “cone of influence” area for a ceiling-mounted panel heater, which extends to a 6.5m span beneath a central room panel location.
Case Study 3(see) explores the improved uniformity of both room heating and reduced variance in relative humidity, together with leading to a more significant ‘comfort’ factor achieved by IR heating compared with either classical convection heaters or fan heaters, offering the prospect of better managing the micro-climates operating within a room. Further work is in hand to look at& quantify health aspects, especially relating to avoiding mildew formation, asthma relief by obviating house-dust-mite ‘detritus’ circulation and the potential to minimise the risk of interstitial condensation and consequent decay in building component structures. Simply changing the heating system toIR panels could greatly simplify the design & selection of modular structural components! Watch this space...
Case Study 4 (see)gives an initial insight into the (limited) impact that increased levels of forced ventilation have on the transmission of IR radiated energy within a room. The effect of increased ventilation on perceived ASHREA comfort levels is negligible! This can be of great importance to architects and designers when seeking to address the ‘healthiness’ of buildings post Covid-19, a need recently highlighted by Sir Patrick Vallance, the UK Government Chief Scientific Advisor.