CASE STUDIES

ENERGY EFFICIENT INDOOR AIR QUALITY (I.A.Q.)
SUMMARISED PERFORMANCE RESULTS OF HEAT RECOVERY VENTILATOR IN CLASSROOMS 13 & 14 at THORRINGTON SCHOOL CHRISTCHURCH 1995 (Headmaster Mr Gavin Price)

There are two adjacent classrooms, one has conventional heating for a "portable" classroom ie ...... 2 x 3.4 kW Unidare fan assisted night store heaters.

The other classroom has one, Unidare 3.4 kW, and an Air to Air Heat Exchanger, (custom made for the classroom dimensions), with an air flow for 31 persons occupancy. (In accordance with the requirements of NZS 4303, i.e. 8 lps per occupant).

Avon Heat Exchanger "cores" have been specially made for NZ conditions, to avoid becoming a "Nuisance Heater" on warmer days when ventilation (without heat recovery) is required. The cabinet is acoustically designed to limit the noise ie .... NC 35, within the classroom.

The heating system (without the Heat Exchanger), was datalogged throughout much of the winter of 1995. The HEATEX was installed 30-8-95, then results were datalogged for both classrooms, over a wide range of outdoor ambient temperatures, including three consecutive days of 4°C, 5°C, and 6°C. On some days the outdoor ambient started quite cool in the morning and increased to over 24 °C as the day progressed.

Without the Heatex, air quality within both classrooms consistently passed 1000ppm CO₂ within 45 minutes of occupation. When the HEATEX was ON, the classroom IAQ was controlled close to 1000ppm. (It exceeded 1000 ppm because the class had 34 occupants, not 31 we had been told was the maximum to design the equipment for). Without the HEATEX, CO2 reached the 3000ppm limit of the datalogger by approx 10.30am each day. (see CO₂ Comparison).

A beneficial side effect of Heat Exchangers is a reduction in humidity. Reduced humidity means a more healthy environment (see Relative Humidity)

We have subsequently monitored many other classrooms, and find that the results are comparable, with the results recorded at Thorrington School.

Energy recovery is significant for most of the school day, (see HRV Performance & HRV Efficiency). The year round average for Christchurch is 12°C, so energy recovery will occur for most of the school year.  No other heating was added to the classroom (except the one, 3.4 kW night store heater).   Body heat from the pupils contributes a significant heat effect for the first (approx) 45 minutes after initial occupation in the morning, then stabilises to a lower, but constant capacity, providing very useful heat, via the HEATEX.  The annual energy saving is approx $190 to $240, per annum, per Classroom.

Any other means to control CO₂ to 1000ppm, (NZS4303), must add at least that energy demand ($190 to $240), to the existing operating costs of the Classroom.  HEATEX can ventilate, & make genuine savings by recovering, & recycling low grade heat that is wasted by other ventilation systems.

Heatex cost varies, depending on site difficulties. Several classrooms can be ventilated by one system . A three stage (say 6kW, 7.5kW, or 9kW) element bank can replace other heating (often infra red), and so deliver only the exact amount of additional heat that is required, i.e. is the most energy efficient electric heating method.

We invite enquiry on any HEATEX application