Technical Case Study 2

The Spatial Distribution of Warmth Within A Room

This study complements Study 1; it determines the spatial distribution of warmth within a room created by a single 800W ceiling mounted panel heater.

It shows that almost 90% of the total room volume (of 69m3) achieves an ASHRAE comfort factor of between 0 and +1. Only the lower room extremities failed to reach this level, but they stillachieved a level of around -0.5 which is classified as “marginally cool”.


Study details:


This study was carried out on 25th March 2021, for which weather records show a cool, cloudy day with showers in the afternoon– Max 10oC/ Min 1oC/ passing clouds with SW/SSW winds of14-23mph. Pressure 1017 mbar falling to 1007 mbar.


A single 800W IR panel heater was ceiling mounted in the mid-point of a test laboratory, described more fully in case study 3 (see).


This laboratory was situated in the same 1960’s building as perCASE STUDY No1, but in a laboratory room measuring approximately 69 m3, but otherwise of comparable construction but marginally inferior U value tothat covered in Case Study 1 (see). A value of 2.5-2.6 was estimated.


The heater was powered using a standard AC mains supply at nominal 240V/ 50cps and covered an 8-hour testing period.

Figure 1: cross-section through 1/2 of laboratory showing  the spatial heating characteristics of a single (ceiling mounted) 800W IR  panel heater.



Note: the hashed line demarcates the recorded temperatures at which Case  Studies 1 & 3 observed ASHRAE comfort factors of at least 0 &  upwards. See footnote below[1].

The vertical axis in figure 1 shows the room height in metres at which the suspended measuring sensors were located.

The horizontal axis shows the width (in metres) of (half of)the room in which the ceiling mounted 800W heater panel was located.

The ceiling mounted panel heater is denoted by the thicker black line above the top left measured cell.

The numbers shown in each cell were the actual temperatures recorded (in oC) in the corresponding actual location.


Temperature data was collected using EL-USB-1 sensors.



Approximately 90%of the 69m3 room, in direct line-of-sight of the 800W panel, registered ASHRAE comfort factors[2] of between 0 and +1. This is in spite of the estimated U value of the room being2.5-2.6, which is appreciably lower than current building standards.Conventional thinking would be to install around 1600-1800W of convective heating into a room of this size.

ASHRAE comfort factor scale

+3 = much too warm

+2 = uncomfortably warm

+1 = comfortably warm

0  = comfortable

-1 = comfortably cool

-2 = uncomfortably cool

-3 = much too cool