Carbon Conservation & Energy Efficiency


Bruce Rowse & Team

Posts Tagged ‘economy cycle’

What will make zero net energy office buildings affordable by 2020?

Wednesday, September 16th, 2009

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.

How to cool for free

Wednesday, July 8th, 2009

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:

The actuator motor in this photo has come off its shaft and is hanging uselessly from its cord

The actuator motor in this photo has come off its shaft and is hanging uselessly from its cord

  • 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.

Diagram showing how a simple free cooling system can be fitted into a server room currently cooled by split system air conditioners. A controller will close dampers, shut down the fan and start the split system if outside air can't keep the room cool

Diagram showing how a simple

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.