INTRO
The concept of controlled ventilation in the home became established during the growth of ‘passive house’ building in the late 1990’ sand early 2000’s onward, along with building ‘air-tightness’ into new-build homes, with high levels of insulation, pre-warming input air via a mixture of solar PV & ground-source heat pumps & with heat recovery from the ‘exhaust’ airflow.
The advent of Covid-19 raised medical concerns (as recently voiced by Sir Patrick Vallance, the UK Govt Chief Scientific Officer), that air-tightness of homes/ communal buildings and air-borne viruses are inconsistent with public health needs.
However, a general response of the public has traditionally been to block-off any such ventilation sources to avoid “wasting” precious amounts of heated air. Infra-Red heating solves this problem, as you can have the benefit of increased ventilation with virtual no loss in room heating efficiency.
EXPERIMENTAL CONCEPT
This current study has been carried out, as a quick initial preview, to check the impact of (relatively high levels of) forced air-displacement on radiated IR heat, since (in theory) there shouldn’t be any impact. This is because (as already covered in previous case studies) IR energy doesn’t heat the air it passes through as radiant energy ‘waves’, heating only the bodies in the room.
A FLIR thermal imaging camera was positioned ~2 metres from a 600mm x 600mm, 650W 2DHeat infrared panel (without frame or rear lagging). A 14” diameter, 48W, mains powered fan was positioned part-way between the camera and the infrared panel with the fan blades 300mm from the front face of the panel. The centres of the fan and the panel were at the same height and the airflow was across the face of the infrared panel. The panel was connected to the mains supply at nominal 240Vac. The recorded image sequence was at 10 second intervals. This set-up was located in an open (otherwise unheated) workshop of~1200 m3.
Effect of forced ventilation on 650W Infrared
RESULTS
The average temperature of the panel was measured at 104.9°C for the 30 minutes before the fan was switched on. The above graph shows the temperature sequence from 2 minutes before the fan was switched on to the point when the fan was switched off. After the fan was switched on the average temperature dropped steadily over 6 minutes to a low point of 98.7°C and then slowly recovered to an average temperature of 99.8°C over the final 10 minutes.
Whilst a drop of ~5oC in surface temperature was recorded (due to the forced cooling of the airflow across the panel itself) nil detectable impact in ASHRAE comfort factor was discerned by an observer positioned alongside the FLIR camera – as theory would predict.
CONCLUSION
IR heating would appear to be a viable heating solution in buildings where increased levels of ventilation might be required for medical safety reasons.