Background info, Costs and Savings

The department currently (October 2009) operates 450 desktop PCs. This is the primary area where savings may be possible. Almost all other IT equipment is providing services and is needed/expected to be available 24x7x365. Equipment such as printers that may often be idle out of core offices hours already drop into energy efficient modes.

Before looking at the current usage it is interesting to look at the savings already made. If we look back 5 or so years then a typical desktop system and monitor was running at approximately 200W when in use. This might have peaked at say 300W if heavy computation were in progress and been lower when the machine was idle (although the systems did not have such efficient energy saving modes then).

The latest desktops and screens purchased by the department are intended to be naturally more efficient, especially when they are sitting idle but on.

Our typical desktop being used for normal activity (e.g. email, web, office applications and document preparation, light computation etc) runs at 60W. This increases to around 90W when significant computation and other heavy usage is in progress. The 24in TFT monitors run at about 40W when displaying an image. This drops to less than 1W when the screen blanks. When a machine is shutdown, but still on at the wall, it runs at about 4W whilst on standby.

Older system also had small separate speakers whereas almost all TFTs now in use have built in speakers. The old separate speakers if left on standby might still be running at 2-4W. Whilst this is comparatively small over a year this needless extra usage adds up. Separate speakers have in general thus been phased out in the last few years.

The usage pattern across the department is very varied but on the whole significant long running computation is run on the compute servers. If we look at the typical state therefore, a computer in use now only runs at 100W. As such the power used by a single machine has already been halved in recent years without even taking into consideration that when idle the new machines are likely to be more efficient than the old ones. This reduction in consumption per PC has of course been more than offset by rising energy prices and increases in the number of PCs within the department. We are, however, at a point where anyone with a desk who wants a PC can have one and thus the growth in numbers of desktop PCs is now almost entirely driven by the growth of the department overall.

In summary:

  • typical PC in use: ~ 100W
  • typical PC on but idle with screen blank: ~ 60W
  • typical PC and screen on standby/soft off power: ~ 5W

Since the working pattern of different people within the department can vary dramatically it is difficult to define a typical user. However, it might be reasonable to define the average/typical usage to be in use 10 hours per day for 5 days a week. These hours will be overly long for many but should represent a reasonable bound and offset higher than expected usage by those that run computations regularly/continuously, work long hours or work at the weekend etc.

Thus in a typical 10 hour working day a single PC would use 1kWh, i.e. one unit of electricity. Over the week the PC would use 5kWh whilst active and a further 7kWh during the 118 hours when not in use. As such each week a single PC is using approximately 12kWh and hence over the course of the year about 600-650kWh (or units of electricity).

If instead the 118 hours when the PC is not in use it were in standby it would only use 0.6kWh per week. Over the course of a year the PC would thus use about 280kWh, i.e. a saving of approximately 55%.

One should also not forget that 1kWh of UK Grid electricity (i.e. one unit) causes the emission of 0.537 kg CO2 (a measure of greenhouse gas emissions). As such any reduction in electricity used not only saves the department money but also results in a reduction in our demand on the planets resources and hence a reduction in our contribution to greenhouse gases (which is becoming ever more obviously important).

Overall costs and savings

If a typical machine uses 600-650kWh (or units) per year then at present our 450 desktop PCs consume about 280000 units per year. If a unit costs on average about 11p then the annual bill would be about £30k. If we simply managed to save 33% that would still be a saving of about £10k, which whilst not huge is significant.

It is worth noting people may also think they should physically switch o ff screens at the wall reducing the power usage from less than 1W to zero when not in use. The saving would be very small since the new screens consume nearly no power when in standby anyway. Doing this can also lead to problems such as inaccessibility of sockets and switching off the wrong item etc. Furthermore, many desktop systems now autodetect the screen resolution and as such the screen needs to be in standby mode anyway (i.e. on at the wall and on at the power switch on the screen) whenever the PC is in standby mode. As such we have decided for now, monitors should also be left to go into power saving mode and not turned o ff either at the front or wall.

Putting the potential savings into context, the departmental electricity bills indicate the annual usage to be in excess of 800000 units (based on figures available for 2009) and thus the desktop PCs account for about 35% of the total usage. Thus if we initially reduce the electricity consumption due to desktop PCs by 33% then the overall departmental electricity consumption might reduce by about 12%. Of course with ever increasing energy prices the reduction in use may not see a similar reduction in actual cost.

One would expect that another signifi cant proportion of the electricity bill is made up of the cost of air conditioning in the summer and additional heaters in the winter. Reducing the time that PCs are on could have some eff ect on this, e.g. each PC when active is broadly equivalent to adding an extra person into the room generating heat. During the day the room occupancy is eff ectively double the number of people in terms of heat output from their presence. During the night, however, when people are generally not in, an idle PC is still like having half a person per PC in the room generating heat and thus the base temperature of the room remains slightly higher than it would were there no PCs. As such in the summer the rooms will now not be quite as hot and there may be some saving on air conditioning (although in practice people tend to turn air conditioning on and leave it running even when it is not always really needed). However, come the winter the reduced heat in some rooms may result in higher usage of heaters offsetting this (particularly when people arrive and a room is potentially colder than expected, they may even then overheat the rooms having turned a heater on and left it running longer than really needed). Any new building would of course be much better at managing and maintaining a comfortable temperature and thus one would expect the temperature on arrival to be as required and additional heaters not to be used. As such the cost of extra heat that may be required to o ffset the heat no longer being produced by the PCs would go against the buildings overall heating cost but this would typically appear on a gas bill and gas is generally cheaper than electricity.

Equipment procurement and recycling

As mentioned above, when purchasing equipment efficiency is one of the factors taken into account. In general when considering desktop purchases, as well as the machine spec and price, typical factors that influence our choice include small form factor, low noise and general energy efficiency/low power needs. The desktop must have a power supply that is rated 80 plus. The monitor will typically be rated TCO'03, which among other things, means it uses less than 1W in standby mode.

When equipment is retired from use in the department appropriate measures are taken to decommission the item after which it is generally placed in one of the `Free to a Good Home' areas where anyone may take items (provided they then take them out of the department). This approach results in new homes being found for almost all old equipment in working order and thus only very small amounts of WEEE ultimately requires disposal.

Actual Results

The graphs of the number of PCs on/off show that as the scheme has been rolled out and become established typically only 25% of desktop machines are on overnight and at the weekends. A simple calculation based on the consumption figures and usage patterns assumed above would indicate this should lead to a 44% reduction in the electricity usage by desktop PCs and and thus a saving on the overall departmental electricity consumption of about 15%. The department currently only has online access to electricity usage figures for one of its 3 large buildings. In the case of that specific building the actual measured savings are 20-25% which is very encouraging.

Other green initiatives within the department

All printers within the department were renamed in 2009. The new naming scheme is to give printers tree names. This a small and subtle reminder to user that when they use printers they are using the resources from trees.

The department is also reviewing its use of air conditioning and will be introducing guidance/policy on appropriate use. In particular this guidance encourage the use of opening windows rather than turning on air conditioning but if air conditioning is used specifies that it should be set to only cool the room to 25°C and turned off when leaving the office.