What is a comfortable office temperature – and why this is very important when it comes to reducing carbon emissions
Changes to temperature settings are a little known but easy way of getting significant carbon savings in offices.
In office buildings the single largest energy user is the heating, cooling and ventilation system. This system will typically account for 40% to 60% of the buildings energy cost and greenhouse gas emissions. A major determinant of how much energy your system uses is the temperature at which it is set to operate. Depending on climate, most offices are set to maintain a year round temperature of either 22OC or 24OC.
Hobsons Bay City Council in Melbourne had temperature settings at the Hobsons Bay Civic Centre adjusted by CarbonetiX engineer Linton Hartfield to allow the temperature to vary between 20 and 25 degrees Celcius. Electricity metering of the air conditioning system showed a 25% energy saving on the packaged heat pump units supplying the building. The air conditioning temperature changes occurred a couple of months after a building extension – which had increased electricity consumption by 10%. According to Environment Officer Rowena Joske, “After the temperature adjustments the electricity bills dropped back to what they were before the extension.” In other words simply adjusting the temperature settings has cut carbon emission by 10%.
Temperature complaints are, however, a major bane to facility managers who can’t seem to keep everyone happy. Do adjustments to temperature settings increase the number of complaints? In the case above more complaints did occur about it getting above 25 degrees in some parts of the building. So the system has been adjusted back in those parts of the building to limit the maximum temperature to no more than 25 degrees.
Comcare, a federal government organisation for public sector employees, has produced guidelines as to what a comfortable office temperature is. According to Comcare the acceptable range of office temperatures is 20 to 26 degrees Celcius, with 20 to 24 degrees recommended in winter and 22 to 26 degrees recommended in summer.
In temperate and cold climates in Australia allowing the temperature in the office to float between 20 to 24 or 25 degrees will significantly cut energy use and carbon emissions as compared to setting the system to maintain exactly 22 degrees. In hotter climates allowing the temperature to go up to 26 degrees instead of making it stay at 24 degrees will similarly save energy and carbon emissions.
For offices in terms of carbon reduction per dollar spent it doesn’t get much better than changing building temperature settings.
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The average double fluorescent light fitting (probably like the one above your head right now) uses $800 of electricity over its life time.Tags: deadband adjustment, energy saving, HVAC - heating, ventilation and air-conditioning, temperature
December 9th, 2008 at 10:57
Raising temperatures setpoints to gain energy efficiencies nearly always comes at the expense of human comfort conditions, in particular space humidity. The reason for this is the way that conventional HVAC systems deal with latent loads.
With a conventional system, %RH is controlled in a default manner by maintaining 7-8degc chilled water temperatures, resulting in 15-18degc supply air that often has to be heated to maintain conditions of 22degc in the space.
In many places in Australia this occurs all year round, and is the main cause of simultaneous heating and cooling, the biggest consumer of energy in buildings.
To understand the relationship between latent and sensible loads, (or temperature and humidity) and the effect on human comfort, you need to understand the ASHRAE comfort envelope.
The comfort envelope demonstrates that when raised temperatures are combined with higher humidity in the space, conditions fall outside the comfort envelope, and people will feel uncomfortable.
The ASHRAE comfort envelope shows that for winter, the upper human comfort limit is 23degc/60%RH, and for summer 25degc/60%RH.
Controlling %RH and temp independantly so that space humidity never exceeds 60%RH, has proven that significant gains in energy efficiencies can be achieved by raising setpoints to the upper limits, without any detrimental effect on comfort.
There are several systems on the market that control in this manner, ie. decoupling sensible and latent loads. We have found the most econimical of these is the Shaw Method of Air Conditioning (SMAC) which is a relatively low cost, high performance retrofit solution for conventional HVAC systems. For new projects, and combined with Induction VAV’s, it is also an econimical alternative to passive systems that will achieve similar, if not better results, and offers far more flexibility if tenant changes are to be considered in the future.
In certain ambient conditions, SMAC enables resetting of chilled water temperatures up to 15degc, resulting in significant chiller energy savings, and virtually eliminating the need for heating/reheating, gaining further savings.
In addition, the elimination of the simultaneous heating and cooling effect results in a more even spread of temperatures accross the space, enabling fan energy savings to be can be achieved by the ability to dynamically control and lower fan static pressure.
On projects to date where SMAC has been implemented, significant energy savings have been achieved and tenant conditions in the space have been vastly improved.
SMAC clearly shows that there does not have to be a compromise between energy efficiency and tenant conditions.
Craig Ryan
National Manager Energy & Sustainability
Johnson Controls Australia
December 9th, 2008 at 11:17
Thanks for your comments Craig, can SMAC be used with packaged systems?
December 9th, 2008 at 9:00
SMAC was primarily developed for HVAC systems with central chilled water plant. SMAC works on the principal of dual cooling coils piped in series, which enables the ability to control humidity (latent loads ) & temperature (sensible loads) independantly.
This same principal can also be applied to DX plant with the installation of an additional coil, but currently there is nothing like this readily available on the market. Johnson Controls are currently working with SMAC Technologies to develop this via our York brand.
SMAC Technologies (08) 8363-3155 have installed a pilot project with custom SMAC DX units at a hospital in Thailand with great success.
I believe this is the only installation where SMAC has been applied to packaged systems.
July 8th, 2009 at 9:09
[...] tight temperature settings with a narrow deadband (see an early blog post on what is a comfortable office tempature for more on [...]