In my previous article I introduced some possible ways for a business to build a reputation as eco-business and I concluded that if a company really wants to stand out it needs to do something extraordinary which is not just the mainstream. But what can it be in practice?
Let's assume this company needs a small office. An effective way for showing a concrete commitment would be to have the office premises themselves up to the standard. If anyone says that they would like to save energy, contribute to cut CO2 emissions and do something valuable for the environment, the best way to start is to improve the quality of the places where they live and work, since buildings can be among the worst gas guzzlers we can think of.
Now, let's try to design at very high level a possible solution for a smart workplace. The hypothetical commercial building which I am going to analyse will have the following main characteristics:
- three levels
- a reception room, a conference centre and an office at ground floor
- two offices at the first floor
- three offices at the second floor
The goal is to get this building as independent as possible from gas and electric grids. In fact, it will not be connected to the gas grid at all and it will need very low (or even none) input from the electric grid. Ideally, the building itself will produce a surplus to be sold to the electric grid.
To achieve this outstanding result, a number of different technologies and construction techniques turn out to be necessary.
The first target is to make the building as thermally efficient as possible, which means that it should need very little energy to get heated in winter or cooled in summer. For this to happen, three main technologies will be adopted:
- insulation
- air-tightness
- mechanical ventilation system with heat recovery
Figure 1 - Passive House technology (source Passive House Institute)
Insulation is a construction technology by which very little heat gets through the external envelope of a building. The external envelope is formed by any external fittings like walls, windows, the ground floor slab, the roof. For every external surface, modern construction solutions must be used to have very little heat transiting in either direction through the envelope.
Air-tightness is a construction solution to prevent air from filtrating through the building envelope. Air-tightness is different from insulation since insulation prevents the heat passing through the envelope while air-tightness prevents the air passing through. There are several reasons why the building should be air-tight. Drafts in indoor living places
- lead to damages caused by condensation and damp
- usually create unpleasant conditions for the occupiers
- prevent a good mechanical ventilation system from working effectively
A mechanical ventilation system with heat recovery is central to achieving a good result in terms of energy efficiency. Instead of relying on air infiltration through window and door frames, the air circulation is forced by fans. The polluted air from inside gets pumped out of the building through a counter-flow heat exchanger. Another air pump introduces fresh air coming from outside through the same heat exchanger. If the air from inside is warmer then outside, the heat exchanger makes the fresh air from outside warmer before it comes in, while, if the air from inside is cooler, the warmer air from outside gives up heat to the air getting out of the building and it becomes cooler. This way, the heating (or cooling) required for maintaining constant the temperature inside the building is minimal (see figure 2).
Figure 2 - A counter-flow heat exchanger
This standard, known as Passive House (or Passivhaus in German), is well proven and has been used throughout Europe for 20 years. It can suit different kinds of buildings, either residential or commercial, and it gives the possibility to save up to 80% of the heating energy if compared to modern low energy standard buildings, and up to 90% if compared to the average German building stock, which is much better quality then the average building stock in the UK. These figures have been measured analysing a big number of Passive Houses in different locations for many years.
The Passive House standard has been defined by the Passive House Institute. According to the institute, a Passive House is a building for which thermal comfort can be achieved solely by post-heating or post-cooling the incoming fresh air, which is required to fulfil sufficient indoor air quality conditions, without the need for recirculated air. For European passive construction, a building can be defined as a Passive House if its annual heating consumption is less than 15 kWh/m².
Furthermore, the combined primary energy consumption of living area of a European Passive House may not exceed 120 kWh/(m²a) for heat, hot water and household electricity.
With this as a starting point, additional energy requirements may be completely covered using renewable energy sources.
We have just seen how we can build an extremely thermally efficient building, but now it remains to find out how we can generate the little power required to heat the office premises and the rest of the energy required for hot water and office equipment.
For this purpose, I've worked out a hypothetical solution for Zero Emission Workspace. This will be a good starting point to understand what it takes to power a small commercial building by using only renewable resources.
Figure 3 shows the 3 storey building front section. The hot water is provided by thermal solar panels, while the electricity needed for the building is generated on-site by a mix of renewable energy sources: PV solar panels, a wind turbine and an optional CHP unit. A rainwater harvesting system is also used to filter and re-use rainwater for internal need.
Figure 3 - Zero Emission Workspace, front section (click on the image to enlarge)
As said previously, the building will be designed and realized according to the Passive House specification and, for this reason, an air-tight envelope and an excellent insulation with elimination of thermal bridges will ensure that the premises can be heated and cooled by 3 counter-flow heat exchangers, one on each floor. The good quality of the air will be ensured by a ventilation system, which will be designed for maximising the efficiency of the heat recovery mechanism.
The floor map in figure 4 illustrates a hypothetical ground floor layout. The total area for each floor will be 600 m2, giving a total of 1800 m2 for the whole building. There will be common areas like a reception hall, corridors, toilets, shower rooms and a lift as well as a conference room and a 220 m2 office. Figures 5 and 6 show the first and second floor respectively, with other offices of various sizes.
Figure 4 - Zero Emission Workspace, ground floor (click on the image to enlarge)
Figure 5 - Zero Emission Workspace, first floor (click on the image to enlarge)
Figure 6 - Zero Emission Workspace, second floor (click on the image to enlarge)
Now, the main question is: what's the annual electricity consumption of these offices? And what's the annual consumption of the common facilities, like the ventilation system and lighting?
To help in this calculation, I've designed a hypothetical office layout for the 220 m2 office at ground floor, as shown in figure 7. The unit consumption in KWh/m2 of this office will then be used to estimate the total office space consumption of the building. A separate calculation will be worked out for the common building consumption.
Figure 7 - Zero Emission Workspace, office 1 layout (click on the image to enlarge)
Table 1 shows the typical energy needs in an average office: computers, printers, telephones, projectors and other office equipments and kitchen appliances. For each office equipment or kitchen appliance I've tried to estimate a typical weekly usage in order to calculate the annual energy consumption knowing the nominal power of the device. For each one of them I have also provided the source of my figures, so to demonstrate that this computation is reproducible by anyone.
Table 1 - Zero Emission Workspace, office 1 estimated electricity consumption (click on the image to enlarge)
In one of my next articles I'll go through some of the most interesting entries of the tables, making some considerations on how we can save electricity by making smart choices in what we use at work. Please consider that the greyed items are not included in the total figures. They are in the table for comparison purposes. For example, I have decided to use laptops instead of computer boxes, mobile phones and soft VoIP telephones instead of actual VoIP telephones and a VoIP switch. In later articles, I will also consider a further reflection on lighting, since many options are available to save electricity depending on the actual circumstances.
But now I am interested in big numbers. I want to find out how much electricity we have to generate possibly on-site to keep this building alive.
Table 2 shows the estimated consumption of all the common building facilities. One of the features I have included in this list is an electric car filling station, depicted in figure 8. This will be formed by 6 car bays, each one fitted with a battery charger. These six electric cars will be available to use for the six offices during working hours. Anyone who needs to do a business trip will have the opportunity to use one of these green vehicles. This will be an extra step towards a real zero emission business. I have estimated a usage of 100 Km per day per car, five days a week.
Figure 8 - Zero Emission Workspace, electric car filling station (click on the image to enlarge)
OK, let's have a look at the results. The electricity consumption per unit area for the office under analysis is 31.9 KWh/m2 per year. Assuming that the other offices have the same consumption per unit area, the total consumption of the six offices is 37860 KWh/year. Adding the common building consumption on top of that, we get to 118517 KWh/year, which is equivalent to an annual unit area consumption of 65.84 KWh/m2.
Table 2 - Zero Emission Workspace, building estimated electricity consumption (click on the image to enlarge)
It is interesting to remember that according to the definition of Passive House set by the Passive House Institute, the total primary energy consumption (i.e. primary energy for heating, hot water and electricity) must not be more than 120 kWh/m² per year. In my estimation, the primary energy consumption is still well below this limit, in fact it is almost half of that. As any good engineer does, let's exaggerate what this building needs by assuming that we want to guarantee an energy buffer big enough. I will take exactly the limit set by the Passive House Institute, 120 kWh/m² per year, which translates into 216000 KWh per year for the whole 1800 m2 building.
Now my next goal is to satisfy this requirement, which means to find a suitable mix of wind power, solar power and possibly other renewable resources to generate 216000 KWh per year.
I am going to find it out. Stay tuned.
