A zero net energy office building is one which consumes no net energy. Its an office that uses very little energy, then has some form of renewable energy to generate all the power it requires.

With current off the shelf solar technology, presuming little or no shading, its possible to get around 100 kWh  of energy per year per square meter of solar panels at latitudes of around 40 degrees, more in sunny locations at lesser lattitude. For a single storey building, with a roof covered with solar panels, and little shading, keeping office energy consumption to 100 kWh/m2 is easy, and in fact I’ve audited quite a few small offices that are nothing special but only use in the order of 100 to 120 kWh/m2. But a grid connect solar system nowdays costs in the vicinity of  $700 to $1,000 per square meter, which is pretty  expensive, so there are very few zero net energy offices in existence.

Aggressive energy conservation and use of off the shelf technology (like skylights) can mean that office energy consumption is kept down to somewhere between 30 to 50 kWh/m2, meaning only half the roof needs to covered with solar panels, or allowing for some shading. For example our office uses only 30 kWh/m2/year, but is shaded in winter, we could make it energy neutral now just by covering around 2/3rds of the roof in solar panels.

So it is possible now, in 2009, to have a zero net energy office, but its not easily affordable, yet. And if your office is 3 storeys or higher, its becomes very hard to achieve no matter what your budget.

Technological advances however, are happening rapidly and I believe that by 2020 a zero net energy low-rise office may be affordable. And importantly this should be achievable by retrofitting an existing office building, with no need to especially construct a new building. Some of these technological changes are:

• The emergence of LED lighting. Assuming by 2020 we have LED lighting of around 200 lumens per watt. Allowing for some daylighting, and good use of task lighting, it may be possible to have annual lighting use less than 8 kWh/m2/year.
• Computer efficiency improvements. Assuming that with thin client architecture and high efficiency monitors by 2020 an office PC uses 15 watts, and that a 200 watt server can then serve 30 clients, computer energy use would be around 3 to 4 kWh/m2/year.
• There are many likely pathways for HVAC, which will depend on climate. A likely pathway for temperate climates is 100% fresh air HVAC systems, with air to air heat exchangers, but also using legacy internal ducting to allow high flow full economy cycles. Fans will be highly efficient, and heat pumps will have high efficiencies at a range of loading conditions, with the conditioning of air separated from ventilation to lower fan energy use. Couple this with light weight retrofit phase change materials (PCM) to provide thermal mass (eg plasterboard with encapsulated PCM), white roofs (where there are no solar panels), glazing treatments and new insulating membrane technologies to improve the thermal performance of the building. Seal the building well, and combine with good use of sensors and intelligent control all of which limits HVAC energy use to say 15 kWh/m2/year.
• Miscellaneous loads: high efficiency fridge at say 150 kWh/year; near zero standby loss hot water system; high efficiency multi function devices, totalling say 4 kWh/m2/year.

This will result in total office energy use of around 30 kWh/m2/year.

With aggressive energy conservation occupants should be able to to get down to say 15 to 20 kWh/m2/year.

Assume solar panel efficiency is more than double current efficiency and the installed price per watt of a grid connect system is one third of the current cost. This will provide 260 kWh/m2/year at a cost of say $500 per square meter.

A single story unshaded office where aggressive energy conservation is practiced will then need only 8% of its roof covered with solar panels, at a cost per square meter of building area of only $40.

A three storey half shaded office building would need most of its roof covered.

It should be possible to have a 7 storey building energy neutral if unshaded and the roof is covered with solar panels. Of course if additional solar panels can be added to walls it should be possible to get even taller energy neutral buildings.

By 2020 the net zero energy low-rise office building should be easily affordable, and in fact it may well be standard good financial practice to convert existing office buildings to energy neutral ones. So even building owners with no interest in acting to slow climate change will have energy neutral buildings. And most low rise office buildings then - whether they are 100, 50, or 1 year old -  could be energy neutral.

I say “should” and “may” because I still have some doubt as to whether a couple of the technologies that modify the thermal performance of a building –  particularly PCMs, and retrofit membrane’s that improve its insulation properties – will be affordable. But then again with focus a lot can change in 11 years, and as more of us demand better energy performance from our buildings I believe that this will spark the innovation needed to make zero net energy office buildings common place.

You can help make this a reality by acting now to make your building more efficient. Do what is affordable now. Then repeat regularly - technology is now advancing quickly. You’ll create the demand that will drive the innovation that will create the technology that will make energy neutral buildings common place.

A recent Sustainability Assessment job took me to the corner of Victoria to the town of Mildura.  A town of around 30,000 people, Mildura borders NSW on the Murray River.  In summer the maximum temperature averages over 30 degrees and naturally there is a high demand for air conditioning and water.  Conventional air conditioning systems contribute substantially to greenhouse gas emissions through the consumption of electricity (predominantly generated from burning coal) and water, for cooling towers and evaporative cooling systems.

The idea of solar air conditioning was mentioned, which sounds great, but does it exist and is it practical?

After doing some reading, yes, solar air conditioning does exist, but despite Australia’s sunny climate there does not seem to be much awareness, knowledge and skills in this area.  So how does it work and why isn’t it widespread in Australia?

From my understanding, there are essentially two categories of solar air conditioning.

1. Ventilation based systems that use photovoltaic power to power fans via heat exchangers or  through desiccant filters  that remove moisture from the air and improve thermal comfort and;
2. Solar thermal systems that harness the sun’s thermal energy (heat) to drive the cooling system.

Photovoltaic powered ventilation based systems are very much dependent on climatic conditions and building design.  These kinds of systems take advantage of fresh air intake to a building and remove unwanted levels of humidity, improving thermal comfort and reducing cooling (heating) requirements.  These kinds of systems have generally been adopted for smaller-scale applications, including the residential market.  This form of solar cooling does not actively cool the air supplied to a building space and is therefore limited to the right environmental conditions to work effectively.

Solar active thermal systems are expensive, more complex and generally too big for smaller applications such as residential housing.  The common system uses an absorption chiller, which compared to a conventional compressor based chiller, does not use electricity to power the system, but instead uses solar collectors to heat water that is then used to produce chilled water through interaction with a refrigerant or desiccant solution.  Such systems can also be used to generate hot water for heating requirements and general hot water needs.  Such systems make good sense where ample sunlight is available and for large-scale or remote applications.

Source: http://greensource.construction.com/products/images/0704_11.jpg

Australia has a high demand for air conditioning and therefore a high demand for electrical energy through use of conventional compressor driven coolers.  The high demand of air conditioning in summer puts a huge strain on the electricity network and contributes substantially to global warming through burning fossil fuels and use of refrigerants (which have an extremely high global warming potential) in air conditioning systems.

Why then is solar air conditioning not widespread, at least for large-scale applications?  The main barriers to solar cooling include:

• The high cost of solar collectors
• Lack of skills in solar cooling technology and increased complexity
• Abundant, cheap energy with no environmental cost
• Minimum incentive to reduce peak power consumption

Overcoming these barriers really requires government intervention through subsidies, research funding, introduction of interval metering to pass on peak costs to electricity users and introducing a carbon tax or trading scheme to factor in an environmental cost on energy.

The Australian National University (ANU) is currently developing a hybrid solar air conditioning that is aimed at replacing conventional residential air conditioners.  The design employs a solar thermal powered compressor that can provide cooling and heating just like a reverse cycle air conditioner. The break-through is the ability to generate cooling like an absorption chiller, but without the need for a bulky and complex system.

The system employs what is called an ‘ejector pump’, which is capable of generating low pressure (necessary for refrigeration) and is low cost to manufacture.  A refrigerant is pumped to high pressure and then heated by solar collectors (the same used for solar hot water systems).  The ejector creates a drop in pressure (the cooling effect) by converting the energy in the refrigerant into kinetic (movement) energy by firing fluid into the ejector at supersonic speed.

Source: http://solar-thermal.anu.edu.au/low_temp/solarac/image071.jpg

Amazingly, the only electricity needed to power the ejector unit is 150 watts or 1/10 the power minimum of a conventional air conditioner.  This is set to revolutionise air conditioning as we know it and the project is moving closer to commercial viability.  With the onset of a carbon trading scheme, the rollout of smart meters beginning, energy rates set to increase and summers increasing in temperature, the economic case for this upcoming technology holds great promise.   I certainly can’t wait for this ‘cool’ technology!

A few months ago I wrote a blog posting about how tighter regulation of electricity supply voltages could save Australia 15 million tonnes of greenhouse gas a year.

However a comment on that posting suggested that voltage reduction may not result in any useful savings.

Below I report on the results of an experiment we undertook to identify how much power can be saved, if any, by operating equipment at a lower voltage.

We measured a variety of single phase loads at different voltages. A variable transformer was used to vary the voltage. A German made Power Tech plus plug in power meter was used to measure voltage, current, power and power factor at the different loads. Loads experimented with included typical single phase lights, computer equipment and a fan.

The experimental set up is shown above. Below is a graph showing the results of the testing.

This graph clearly shows that for common lighting loads power consumption decreases with decreased voltage

• Incandescent lamp (resistive load)
• T8 fluorescent (inductive load)
• T5 fluorescent (electronic ballast)

The reduction in power consumption with the T5 fluorescent (with an electronic ballast) was unexpected.

The fan, with a single phase (shaded pole?) motor, also used less power with lower voltage, interestingly the power factor improved as voltage was lowered, with the power factor the highest at 220 volts.

The PC computer and monitor both showed lowest power consumption at 230 and 240 volts, but power consumption generally did not decrease with voltage. Power factor improved a little at lower voltages.

This experiment shows that for a variety of loads power consumption is in fact less at lower voltage.

For heating or cooling loads equipment may need to run longer when at lowered voltage to reduce the same amount of heating or cooling, with no net energy savings.

Three phase synchronous motors are unlikely to use any more or less power (a theoretical assertion, we don’t have the equipment to test), having the motors run at 230 volts rather than 240 or 250 volts however is unlikely to cause motor damage due to excess current as the voltage difference is only small.

But with lighting and many single phase motors power consumption drops with lowered voltage.

My back of the envelope calculations still come up with a saving of around 15 million tonnes of greenhouse gas if voltages were closer to the 230 volt standard rather than being at 240 to 250 volts.

If high voltage drops in distribution were a problem additional network infrastructure could be used to deliver a more consistent voltage across the network. 2009 is the year of the “smart grid.” A smart grid could mean multitap transformers that can be changed on the fly to deliver a more consistent 230 volts across the whole electrical network.

Free cooling takes advantage of cold outside air to cool a warm building. Strictly speaking “free cooling” isn’t free as energy is used by fans to move air from inside to outside. Free cooling is beneficial for any building where there are significant heat loads inside.

Server rooms and data centres can benefit enormously from free cooling, and in fact is the main reason why Google’s major server rooms are located in cold climates. It’s also beneficial for large office buildings where internal heat loads from people, lighting and office equipment mean that the core of the building is warm, even though it may cold outside. Buildings with glazing facing the sun can often benefit due to the heat load from solar heat gain. Its been our experience that in temperate climate’s such as Melbourne even small buildings can benefit from free cooling.

To cool for “free” your building’s air handing system needs to have an “economy cycle” installed. An economy cycle has a large fresh air intake, and also a large spill or relief air outlet. Rather than recirculating most of the air in the building as is normally done, with an economy cycle the air is not recirculated, it simply comes in, provides cooling, then is vented out again.

If an economy cycle is not operating, not only is fan energy used to recirculate the air, but energy is used to provide cold refrigerant or chilled water to coils that cool the air that is being recirculated.

Your building’s air handling system may already have an economy cycle fitted. Its worth while finding out if it does, and if so, if its operating properly. Common problems that limit the effective use of an economy cycle are:

• Very tight temperature settings with a narrow deadband (see an early blog post on what is a comfortable office tempature for more on dead-bands)
• Faulty actuators. These may not be fully opening or closing the supply air, return air and spill air dampers.
• Faulty dampers. Dampers may be broken, rusted in position or seized.
• Controls that can’t enable an economy cycle, even though all the hardware is in place.
• Out of calibration sensors, that don’t call for an economy cycle when needed.
• The supply air vent is located in a warm plant room, so that an economy cycle won’t work even though its cold outside.

On the other hand your system may not be set up for an economy cycle. This is the case with many packaged air conditioners. In this case to get free cooling an economy cycle may have to be retrofitted. This involves increasing the sizes of the supply and spill (relief) air dampers and ducts as needed, the fitting of motorised dampers, and upgrading of the controls.

Small server rooms cooled by split system air conditioners can often be easily set up for free cooling by setting up the necessary duct work. The more equipment in the server room the bigger the savings.

In cold and temperate climates free cooling should always be considered as an energy saving measure.

During our energy audits re will often undertake a detailed system inspection and data logging to verify the correct operation of existing economy cycles, or undertake a cost-benefit analysis of installing an economy cycle if not yet installed.

During energy audits, our team often finds situations where walls or partitions have been moved or an extension has been added to a building and the electrical and mechanical services have not been considered. This leads to reduced occupancy comfort and energy wastage. The major energy saving opportunities lie in the duct design and the lighting layout. The following case study examines the opportunities brought about by re-examining duct design.

(part 1) HVAC opportunities

The following diagrams show a case study of an existing duct layout where an extension has been added on the west facing windows of the office. Measuring the flow rates of the packaged units servicing the area alerted us to the fact that air velocities were excessive and fresh air rates were greater than 10 litres per second per person.

Figure 1 – Mechanical service duct layout with measured diffuser air velocities

What is the affect of high air velocities and what energy saving options does this present?

High air velocities cause wind chill. Wind chill is a convection process which increases the transfer of heat from surfaces such as skin and clothes.

Figure 2 – Wind chill cartoon from
www.r-p-r.co.uk/wind_chill_table.htm

In figure 1, occupants were complaining of feeling cold even though the temperature in the area was measured at a comfortable 23 degrees Celsius.

Rule of thumb

At 25 degrees C, an air speed of 1m/sec will be felt by the body as 2 degrees cooler.

If air velocities are too high there may exist an opportunity to slow the air handling fan down. This can be done via the installation of a Variable speed drive (VSD) or in belt driven fans, by changing the pulley size. Both of these methods result in fan energy savings.

Note: care must be taken not to reduce the air speed excessively in refrigerant systems as this could lead to malfunction or excessive wear and tear on the unit.

It is also important to consider what happens to the fresh air volume when slowing down air handling systems. If the fresh air intake is set to 10% which provided the occupants with precisely 10 litres per second per occupant and then adjustments are made to reduce the air flow rate by 25%, this would result in new fresh air volumes of 7.5 litres which may be too low. In a fixed fresh air system this may mean opening the fresh air damper (if it is adjustable) and in a modulating system, this will require adjustments at the controller or in the Building Management System (BMS).

An alternative to increasing the fresh air rate may exist in installing CO2 monitoring. The opportunities of which will be the subject of a later blog.

In our case study we have identified that there is an abundance of air volume and higher than required fresh air volumes. The small west positioned packaged unit was installed initially to service a different heat load presented by the west facing glass. Since then the building has been extended and the glass is now internal. This has the effect of reducing the heat load on this part of the office.

By simply reviewing duct design, a complete packaged unit has been removed from service!

By measuring the air volumes at each diffuser we can determine the quantity of excess air and how we can balance the system to improve occupancy comfort. Auditing the diffusers also highlighted some areas that did not require air conditioning such a store room, and a copy room that has been retrofitted with its own split system and extraction system (see diagram above). The following diagram shows the new layout of the HVAC ducts. Note that AC unit 3, and 4, have been extended to allow the removal of AC unit 5. By simply reviewing duct design, a complete packaged unit has been removed from service.

Figure 3 – Mechanical services duct layout after changes

It should be noted that this analysis has been made significantly easier because of the access to up to date mechanical services drawings and accurate floor plans. As any alterations are made to buildings it is important to update the floor layouts, mechanical, and electrical services drawings. If your facility does not have up to date drawings, it may be worth while seeking the services of a drafting company to develop a Computer Aid Design (CAD) set. This will allow the facilities department to track any changes as they occur and allow more efficient analysis of problems for contractors which ultimately will result in faster and more comprehensive analysis of problems.