Data for Wellington - Last Updated - 02/09/2016 07:30 (local time)

Adaptive Comfort Temperatures

Adaptive Comfort Temperatures - free running buildings

 Fri 2 SepSat 3 SepSun 4 SepMon 5 SepTues 6 Sep5 Day
Upper24.324.524.624.624.724
Adaptive Comfort Temperature22.322.522.622.622.723
Lower20.320.520.620.620.721

Adaptive Comfort Temperatures - close control buildings

 Fri 2 SepSat 3 SepSun 4 SepMon 5 SepTues 6 Sep5 Day
Upper25.625.625.625.625.725
Adaptive Comfort Temperature23.623.623.623.623.724
Lower21.621.621.621.621.722

5 Day Temperatures

Where set-points need to be adjusted manually using thermostats it may be impractical to do this on a daily basis or to an accuracy of 0.1°C. To cater for this, 5 day values have been calculated from the daily data as follows:

  • Upper comfort temperatures - minimum of the daily values rounded down
  • Adaptive comfort temperatures - average of the daily values rounded
  • Lower comfort temperatures - maximum of the daily values rounded up.

Daily Temperatures

The daily adaptive comfort temperatures have been calculated using the equations given (refer to About this site). The temperatures are for buildings with mainly sedentary (sitting based) activities. Upper and lower temperatures have also been provided as follows based on a comfort band of +/-2°C:

  • Upper comfort temperatures - these may be used as summer cooling system set-points to maximise cooling energy saving as well as free and pre cooling.
  • Adaptive comfort temperatures - these may be used as more conservative set-points for cooling, giving a margin to allow for control bands on the cooling system and variations of temperature across the space.
  • Lower comfort temperatures - these may be used as winter heating system set-points to maximize heating energy saving.

Predictive Pre Cooling Strategies

Strategy Modes

Minimise ventilation "stop" - when outside conditions are too hot, too humid, or too cold then window opening should be minimized to in air conditioned buildings. Minimum opening is usually that needed to provide adequate fresh air into the building.

Conditions are too warm when outside temperatures exceed inside, ie there is no free cooling.

Conditions are too humid when the energy required to dehumidify the outside air down to an inside humidity of 60%RH exceeds any free cooling benefit.

Conditions are too cold when minimum ventilation and fabric losses exceed internal and solar gains. Any free cooling would waste heating energy.

For buildings with heating only the inside temperature would be expected to float above the adaptive comfort temperature on hot days. Typically the inside temperature will exceed outside and there will be no dehumidification, ie conditions will rarely be too hot or too humid.

Free cool "continue" - open the windows to free cool down to the adaptive comfort temperature ("comfort" felt by occupants). In this mode, as much of the cooling load as possible is met by free cooling.

For buildings with heating only it is assumed that the inside temperature will generally exceed outside so free cooling is always available. If outside temperature does exceed inside then ventilation should be minimised.

Pre cool "go" - open windows to maximize cooling introduced from the outside and store it in the building fabric. For pre cooling it is assumed that inside temperature is reduced to the lower comfort temperature, 2°C below the adaptive comfort temperature ("slightly cool" felt by occupants) . This reduction should not be undertaken at the risk of occupant discomfort or bringing on the heating.

The pre cooling mode is selected when there is a shortfall of free cooling to cooling load. The strategy will search back hour by hour to see whether pre cooling is available to meet the shortfall. The search will continue back through the preceding morning and night adding up the pre cooling available. The search will stop when the cumulative pre cooling meets the shortfall, or the end of the previous day is reached. (Many non-domestic buildings are unoccupied overnight so opening windows at night may be impractical - refer to About this site).

Off - out of hours (and no requirement to pre cool).

Predictive Pre cooling strategies - free running buildings with air conditioning

Local TimeOutside Temperature Adaptive Comfort TemperatureLow Gains Moderate GainsHigh Gains
07:0013°C 22°CCool Cool Cool
10:0014°C 22°CCool Cool Cool
13:0015°C 22°CCool Cool Cool
16:0014°C 22°CCool Cool Cool
19:0013°C 22°CCool Cool Cool
22:0012°C 22°CCool Cool Cool
01:0012°C 22°CCool Cool Cool
04:0011°C 22°CCool Cool Cool

Predictive Pre cooling strategy - free running buildings with heating only

Local TimeOutside Temperature Adaptive Comfort TemperatureLow Gains Moderate GainsHigh Gains
07:0013°C 22°CCool Cool Cool
10:0014°C 22°CCool Cool Cool
13:0015°C 22°CCool Cool Cool
16:0014°C 22°CCool Cool Cool
19:0013°C 22°CCool Cool Cool
22:0012°C 22°CCool Cool Cool
01:0012°C 22°CCool Cool Cool
04:0011°C 22°CCool Cool Cool

Calculation Of Pre Cooling Storage/Release

The cooling load is calculated from the internal (occupants, equipment, lighting), solar, ventilation and fabric gains (conduction etc from outside). The ventilation and fabric gains will be negative, ie losses, when outside temperatures are below inside.

The free cooling available is calculated from the inside to outside temperature difference and the maximum ventilation rate.

When the free cooling available exceeds the cooling load, the excess can be used for pre cooling. The pre cooling stored is this excess subject to the maximum rate at which it can be stored in the building fabric.

The release of pre cooling occurs when there is a shortfall of free cooling to cooling load. The pre cooling released is this shortfall subject to the maximum rate at which it can be released from the building fabric.

A maximum rate of storage / release of 15 W/m2 has been assumed for a thermally medium weight building with temperatures variations of +/-2°C.

Previous Day

The requirement for pre cooling can also be assessed from inside conditions the previous day. This is on the basis that if it was warm yesterday, then more than likely it will be warm today. Therefore, when inside conditions have been warm the previous day, pre cooling should be instigated the following night (if practical) and morning unless outside conditions are too hot or too humid.

Air Movement

Air movement from open windows can provide a significant cooling effect. In buildings with heating only it can be beneficial to keep windows open even when it is warmer outside than inside. Where appropriate, this may be accounted for by keeping windows open at outside temperatures up to 2°C above inside temperatures1.

Building Definitions

The strategies are based on the following simplified building definition with low, moderate and high levels of internal gain:

Occupied period
0800 to 1800

Internal gains
15 W/m2 (1.4 W/ft2) low
30 W/m2 (2.8 W/ft2) moderate
45 W/m2 (4.2 W/ft2) high

Solar gains (peak month)
30 W/m2 (2.8 W/ft2) sunny
20 W/m2 (1.9 W/ft2) sunny intervals
10 W/m2 (0.9 W/ft2) otherwise

Solar gains for other months are scaled down on the basis of average monthly global radiation.

Ventilation rates
1.6 l/s/m2 (0.3 cfm/ft2) minimum
5 l/s/m2 (1.0 cfm/ft2) maximum

Fabric gains / losses
1 W/m2K (0.2 Btu/hft2F)

Storage / release
15 W/m2 maximum (1.4 W/ft2)

Strategies for other building definitions and internal gains can be provided as part of our consultancy service.

Notes

  1. "CIBSE Guide A: Environmental Design: 2006".
  2. Values have been calculated based on Met Office recorded data and predictions. In exceptional circumstances where Met Office data is not available, values may be based on average temperatures appropriate to the location and month. Met Office data currently used for R&D purposes only.
  3. Temperature set-points should be subject to other considerations including local regulations, standards and guidance, other requirement criteria such as for equipment or artefacts, maintaining a dead band between heating and cooling systems so as to avoid conflict and energy wastage, localized thermal effects such as radiant cooling / heating close to building facades, etc.
  4. Where cooling equipment is installed for which condensation must be avoided including chilled beams and chilled panels, adjustment should be made to humidity set-points in conjunction with temperature set-points to ensure condensation is avoided. Air at a higher temperature and same humidity will have a higher moisture content and therefore condensation risk. Humidity set-points therefore need to be reduced as temperatures increase.
  5. A comfort band for temperature variations of +/-2°C around the comfort temperature would generally be considered acceptable. Adopting a tighter band would reduce savings while a looser band would increase savings.
  6. Window opening or opening of similar ventilation devices should be subject to other considerations including security, safety, noise, pollution, adverse weather, local discomfort, overcooling bringing on heating, fresh air requirements, etc.
  7. For the purposes of this website the term "air conditioning" is considered to include mechanical cooling and comfort cooling.