The study highlighted in this article introduces an inexpensive empirical method for determining the total thermal resistance (TTR) index of a building by calculating it as a result of measuring the exact heat loss over a short time and recording interior/exterior temperature difference for that same period. The TTR index is calculated with the formula:
TTR = ΔT/Q
Where:
ΔT is the temperature difference in C; and
Q is the heat loss rate in kWh/h.
For example, if the recorded exterior temperature over a span of 24 hours is −20 C and the measured heat loss/consumption is 240 kWh in order to keep the interior temperature at 20 C, then the TTR index, say, for a 40-year-old house in Prince George, would be calculated using the equation above as:
TTR = ΔT/Q = (20 – [−20]) / (240 / 24) = 4
The proposed TTR index accounts for the combined R-values of all building components, air leaks, and dimensions. It can provide a very good indication of the energy needs of a specific house. A high TTR index can mean a well-built home, with good insulation and airtightness, but it can represent low energy needs associated with a smaller house as well.
This works similarly to the rating of cars for fuel consumption. Sometimes, high engine performance alone can be deceiving when assessing the overall consumption of the car. A brand new pickup truck can have very good engine fuel efficiency, but it still may consume a lot of gas because of its size. Nowadays, many energy-conscious people are equally interested in energy efficiency and downsizing their own energy needs. TTR index can be easily converted into actual energy consumption for space-heating by estimating the energy efficiency of the heating system, the exterior temperature, and the desired interior temperature.
For the existing Canadian residential building sector, the research project’s very rough estimates suggest the values of TTR indexes would be on a scale of 1 to 10, with TTR-1 being the most energy-demanding house and TTR-10 the least energy-demanding. The results of this experiment showed Shed 1 with reflective foil as vapour barrier had the highest TTR index (TTR-90) of all shed configurations. This corresponds to the least heat loss or energy needs for space-heating. Shed 2 with poly vapour barrier had the lowest TTR index (TTR-82).
It is evident the high values of TTR indexes in this experiment are the consequence of a small interior space in conjunction with good wall insulation. However, a house may require 20 times more heat than an insulated shed. Thus, the TTR index of a house may be 20 times smaller than the TTR index of a shed—probably in the expected range from 1 to 10.
The calculation of the TTR index should be independent of temperature difference, as it is only a measure of insulation and size of the building structure. For example, replicating the measurements in the same Shed 2 for a second week generated the same value for the TTR index (Figure 5), although the temperature differential was different (DT decreased by approximately nine per cent).
There was no difference in recorded RH between the two sheds (i.e. reflective foil versus poly). In fact, the recorded humidity was quite low—a subsequent study may include humidifiers installed in each shed, which may affect heat transfer as well.
