Before trying to satisfy the energy requirement of the commercial building proposed in my previous article, I would like to take some time to go through the figures I listed in Table 1 (typical office consumption) and Table 2 (typical common building consumption).

Table 1 - Zero Emission Workspace, office 1 estimated electricity consumption (click on the image to enlarge)

Table 2 - Zero Emission Workspace, building estimated electricity consumption (click on the image to enlarge)

Let's analyse these numbers one by one, pointing out some smart tricks to make an office less energy demanding.

Computer boxes

An average computer box has a power consumption of 80W. Using it 8 hours a day for 6 days a week (I have exaggerated this estimate, considering Saturday as a full working day) it is a total energy consumption of 3840 Wh. Considering 20 computer boxes for the 220 m2 office under analysis, it would be 76.8 KWh per week. This would add up to about 4000 KWh/year.

I made the decision to impose a restriction on the use of computer boxes in Zero Emission Workspace, unless there is a specific business requirement for using a few of them. The reason is easy to understand by looking at the energy consumption of the natural alternative: laptops.

Laptops

A typical laptop has a power consumption of 20W. Making the same weekly calculation we obtain about 1000 KWh/year, which is a quarter of the electric energy required by a computer box. Considering the excellent capabilities of modern laptops, the added flexibility and the fact that they come with an integrated screen, I think there is no reason why we should use a PC box for simple office needs. A computer box will be used only if there is a specific requirement like in the case of a server machine.

I have also included 8 extra laptops which belong to guests sitting in the meeting room. I have assumed that all these guests' laptops are connected to the power supply and that they are switched on 4 hours a day, 5 days a week. This turns to be 166 KWh/year.

LCD displays

Even though an LCD screen comes integrated with a laptop, I have considered the option of using a separate monitor in order to extend the size of the computer desktop when someone sits at their desk and connects the laptop to the external screen. The typical 17" LCD display power consumption is 34W. 8 hours a day, 6 days a week, 20 monitors, it adds up to about 1700 KWh/year.

Even though it is likely that something more advanced than 17” LCD displays will be used, it is also true that we expect next generation monitors to be more and more energy efficient. For this reason, we stick to this rather old model for the scope of this estimate.

Projector

A 150W projector in the meeting room, switched on 1 hour a day for 5 days a week, amounts to 39 KWh/year.

Printers/copiers/fax machines

I have considered three different multi-function printer machines: a large Xerox A3 size colour printer/copier/fax machine, 32 images per minute; an A3 colour printer/copier/fax machine from Richo; and a fast mono colour printer/copier/fax machine from Richo (60 ipm). These models seem to be fairly energy efficient machines, according to the Energy Star web site. Assuming that we use all of them in our office, this adds up to nearly 1000 KWh/year in total.

It is surprising to know that a laser printer machine consumes quite a big amount of electric energy even when it is inactive (17W). This is why I have included also this number to my calculation.

Document shredder

Many offices have confidentiality issues and need a document shredder to dispose their internal documents. An average document shredder has a power consumption of 500W while shredding paper. 1 hour of shredded paper per day, 5 days a week, it comes out to be 130 KWh/year.

LCD HDTV screen

Sometimes big screens are used in offices as entertaining TV systems in the kitchen and break-out areas or as showcase monitors playing video clips about company's products and services. Strictly speaking, for the latter use we should also include the consumption of a DVD player, but I have considered just the consumption of the screen, since it is much more. Let's assume we want to entertain 8 hours a day, 5 days a week. For a 170W 46" LCD screen, this adds up to 353 KWh/year.

Microwave

Let's head to the kitchen. Any good office should provide basic kitchen appliances. A microwave has an average power consumption of 1400W. Using it 2 hours a day, 5 days a week, it amounts to 728 KWh/year.

Fridge/freezer

An energy efficient Bosh class A++ fridge/freezer, used flat out 24/7, consumes just 208 KWh/year.

Coffee maker

Waking up people during working hours by using an 800W coffee maker, which brews coffee 2 hours a day for 5 days a week, takes 416 KWh/year.

Water heater/cooler

A 90W water heater/cooler, used in conjunction with a timer that switches it on for 10hrs a day, 6 days a week, consumes 280 KWh/year.

Dishwasher

An average dishwasher used at 55°C, used once a day, 6 days a week, burns off 333 KWh/year.

Computer network

A Cisco 2500 network hub/router has a nominal power consumption of 40W. Keeping it switched on all the time 24/7, it requires about 350KWh/year.

Telephones

This topic is an interesting one. A typical modern solution for an office is to have a number of Voice over IP (VoIP) telephones installed on each desk. VoIP phones are usually powered from a VoIP switch via a technology called Power over Ethernet (PoE). The VoIP switch gives the necessary power through an Ethernet network cable to each VoIP phone in use in the office.

It is not difficult to realize that such a device requires a lot of electric energy. A Cisco Catalyst 3560-24PS can power up to 24 VoIP phones. According to the switch data sheets, a typical weekly energy consumption (24/7) amounts to 73 KWh, which corresponds to 3796 KWh/year. This really looks like a big energy sucker.

What about switching to mobiles? I believe that a modern office doesn't really need VoIP phones. People could argue that VoIP phones come with a lot of fancy features, but the truth is that today a simple smart phone can provide everything a VoIP phone system provides. And for phone conferencing, there are many Internet based solutions hosted by specialized companies, such as Cisco WebEx, Microsoft Office Communicator or even Skype, all of which offer videoconferencing as well.

A comprehensive business solution could be as follows:

  • mobile phones for standard voice calls and voice mail
  • soft VoIP phones for voice calls and online conferencing systems

What would this solution cost in terms of power consumption? A Nokia mobile phone charger has a nominal power consumption of 4W. If 20 people used it 2 hours a day for 5 days a week, it would add up to 41.6 KWh/year. Wow, this is almost 100 times less then using a greedy Cisco Catalyst! As usual, let's exaggerate assuming that people in our hypothetical office are very phone addicted and need the charger plugged in for 8 hours a day. That would mean 166.4 KWh/year, still nowhere near the enormous consumption of the Cisco switch.

Ventilation system

Now we need to consider the power consumption which is not office specific, but rather a whole building consumption. One of the main features of Zero Emission Workspace is a ventilation system with heat recovery, which is described in my previous article. There are a few ventilation systems that are compliant with the Passive House specification. One of these is designed and produced in the US by a company called UltimateAir. Their RecoupAerator 200DX Energy Recovery Ventilator has a nominal power consumption of 40W. Since we need to keep it switched on flat out 24/7, its total annual power consumption is about 350 KWh/year.

This is the consumption of one of them, but it might be the case that we need two or three independent ventilation systems, for example one for each floor. This is something that needs to be assessed at design time; what we need to take into account now is the fact that this consumption could rise up to about 1000 KWh/year.

Lighting

According to a study carried out in 2006 by the Electrical Department of the Université catholique de Louvain in Belgium and the Belgian Building Research Institute, commercial buildings represent more than 40% of the total energy consumption in Europe. A decrease of the European energy demand requires thus a better energy performance of buildings. Lighting installations represent a significant part of this consumption (about 35% of the total primary energy consumed in buildings like offices and schools).

That means we need to dramatically reduce lighting consumption if we want to achieve tangible results in slashing electricity consumption in offices.

Interestingly, the same study found out that using conventional 55W fluorescent tubes in conjunction with daylight regulation dimming systems and movement dependent switching the electricity consumption is lowered by 50%. Assuming 4 fluorescent tubes every 20sqm (Figure 1), 10hrs a day, 5 days a week, it all adds up to 26400 KWh/year (about 31600 KW/year considering 6 days a week).

Figure 1 - Iso-lux curves of 4 fluorescent tubes in a 20 sqm office

There is something to add to the Belgian study. If we substituted all the 55W tubes with 10W energy savings fluorescent light bulbs we could reduce the lighting consumption to 8640 KWh/year. This would be a massive reduction, though I haven't considered this option in my final calculation.

In fact, some studies argue that fluorescent tubes are better then energy savings light bulbs in terms of light spectrum. Even if the latest energy savings light bulbs have a very good natural light spectrum and I believe that for this reason they could be used in offices without affecting negatively people's eyes (LCD monitors 7 hours a day are far worse than any kind of lighting!), we can still think of mixing the two technologies: we may use fluorescent tubes for the offices, where people work and spend most of their time, and energy savings light bulbs for the communal areas like corridors and toilets.

Lifts

Lifts are very hungry energy suckers. A ThyssenKrupp 10K Drive Lift, which is claimed to be an energy efficient lift thanks to a particular motor technology, has a consumption of 87KWh/day with a 35% duty cycle (i.e. used 35% of the time), which means 27144 KWh/year. This is a lot of energy, but the only way to cut it off is really climbing the stairs, which is something we can encourage in a 3 storey building, especially for the first floor or going down.

How many people do actually use a lift without a real need for it? Do we really need to use it going down from the first or second floor of a building?

Obviously we can't force people to use the stairs or stop them using the lift. What we could do though is to encourage using the stairs by giving benefits for every certain number of climbings, like vouchers for monthly gym memberships.

Conference audio system

A 500W Yamaha conference audio system, used 4 hours a day for 5 days a week in the conference room at ground floor, demands 520 KWh/year.

Hand driers

Hand driers are really demanding too. But there are some efficient solutions around. An Xlerator high speed hand drier can dry hands in 10 seconds, thanks to a very powerful air stream.

I have made a calculation considering a typical weekly usage including guests. If the office number 1 at ground floor has 20 permanent employees in 220 m2 and the total office area is 1185 m2, the total number of permanent staff is about 110 people. Accounting also 30 guests per day, at a rate of 3 10 second dry shots per day, it all adds up to 468 KWh/year.

Vacuum cleaner

A 1500W vacuum cleaner used 3 hours a day, 5 days a week, burns off 1170 KWh in a year. I believe that avoiding the use of carpets in commercial buildings would help to reduce the need of vacuum cleaners. Tiles, laminate and linoleum are much easier to clean and they would dramatically reduce the accumulation of dust mites which increase the risk of allergies and asthma.

CCTV system

Typically, commercial premises are protected by some sorts of security systems like alarms or CCTV cameras. I have taken as an example a CCTV system protecting the building 24/7 with a 60W 16 channel Digital Video Recorder, 12 2W day/night cameras, 4 6W high definition cameras and a 30W monitor. This all adds up to 1205 KWh/year.

Electric car chargers

The idea of giving businesses the opportunity to use electric vehicles for some of their business trips might look like an unaffordable luxury in terms of energy consumption. But let's try to do some maths and see what we are really talking about.

A Citroën Berlingo Electrique 500 has a consumption of 25 KWh per 100 Km, while one of the most efficient electric cars, a small Mitsubishi iMiEV consumes 10 KWh per 100 Km. David MacKay, in his book "Sustainable Energy – without the hot air", gives a good list of modern electric vehicles on the market together with their measured consumption. It turns up that the consumption for an average electric car is 15 KWh per 100 Km. Considering 6 cars, 100 Km per day, 5 days a week, it would be 23400 KWh/year. This seems quite a lot, but in fact it is less then the consumption of the ThyssenKrupp lift and very similar to the energy required for lighting. This means that if we could avoid using almost completely the lift (which would also be good for our health in a 3 storey building), we could power 6 electric vehicles, 5 days a week, all year round.

The introduction of a fleet of electric business cars would be a great step towards a zero emission workspace: even part of the business trips would be powered by renewable resources.

The total consumption for a building like the one described here would be 118517 KWh/year.

As I said in my previous article, we need to stretch this number in order to have a good energy buffer in case we need more energy then the estimated one. I decided to set this number to 120KWh/sqm, which is the limit set for the Passive House standard. This amounts to 216000 KWh/year for our 1800 m2 hypothetical building.

How are we going to generate this electric energy on site? This will be the topic of the next article.