In October last year CarbonetiX started an independent evaluation of LED lights as a substitute for fluorescent lighting. LEDs, standing for light-emitting diodes, have previously been commonly used for other purposes such as for low energy indicator lights on household equipment, but have not yet been widely used for general commercial lighting.

The evaluation is being undertaken by CarbonetiX in partnership with the Sustainability Fund, managed by Sustainability Victoria, and with the support of Frankston City Council. Eight months on and the trial is now nearing conclusion.

176 fluorescent tubes were replaced with solid state LED lamps in the Mahogany Neighbourhood Community Centre in the City of Frankston.  Users of the facility were surveyed before and after the upgrade and noted either no change or an improvement in the lighting. An illumination assessment showed that illumination levels after the upgrade were around the same as before. Yet power consumption has dropped from over 40 watts per lamp down to 18 watts.

The trial has involved firstly a desk-top evaluation of LED products, then selection of lamps from those six manufacturers who appeared to have the best products. These were then tested by CarbonetiX for light output and power consumption. The best performing lamp was then sent to a NATA (National Association of Testing Authorities) certified laboratory for photometric testing.

It was disappointing to have the only Australian lamp fail during our in-house testing. However the overall testing result was  surprisingly good: the useful light provided by the best lamp in a standard office troffer was similar to that of a used halo-phosphor tube, whereas our earlier program of testing indicated the LEDs were just not bright enough to be used as a fluorescent substitute.

This means that where a building is currently lit by halo-phosphor lamps, which are still quite common fluorescent tubes, and where the illumination levels exceed those specified in AS1680, that the best LED tube could be used as a fluorescent substitute. 

Another concern was the reliability of the product. Barney Mezey, our energy auditor who ran with the project, was concerned about the headache that failure of the lamps would cause. Fortunately all of the lamps are still working three months after they were installed. Obviously this is nowhere near long enough to establish whether or not the lamps will operate for 50,000 hours or not as claimed by the manufacturer. But it is a good start..

LEDs are still expensive, with CarbonetiX estimating a twelve year return on investment. But this trial indicates that if the technology continues to evolve and prices drop that LEDs could help halve the use the energy used by lighting in commercial buildings.

Once you start listening for climate positive stories or examples you’ll find lots to be inspired by. I’ve heard quite a few of them over the last 18 days. Here are seven quick examples of organisations that have saved money and greenhouse gas by cutting their use of energy.

1. University of New South Wales mail centre – Fuji Xerox helped them achieve a 23% reduction with new copiers and printers / consolidation of machines.
2. Airbus – the new A380 uses 40% less fuel per passenger km than aircraft of 25 years ago.
3. Google server rooms – use less than half the energy of a typical server room of the same capacity.
4. Dell computers saved over USD$1 million by improving the computer switch off practices of its staff.
5. The leading Sustainability Street (a program run by Vox Bandicoot) – cut greenhouse emissions by 49%.
6. Gaden’s Lawyers cut energy consumption by 20% through behaviour change. No capital cost.
7. Logistics company Linfox is aiming to cut its emissions by 15% by 2010. A driver training program is already making a significant contribution to the achievement of this target.

Now that’s climate positive! How much could you save?

(Part Two) The first part of this topic was published on the 8th of May.

Flat Plate Solar Collectors

Flat panel (aka flat plate) collectors work on the principle of copper pipes running through a glass covered collector, often connected to a water storage tank on the roof. The hot water can then thermosiphon itself in and out of the tank, thus heating the water. Finally the hot water is gravity fed into the house from the roof. This is an extremely efficient way of gaining and storing hot water and can be over 90% efficient in the right climate. The simplest combination is the close-coupled system (see photo below).

However, the water tank may be located in the roof space or on the ground as a separate unit in which case a pump is necessary to circulate the water. This is known as a split system. Flat panel collectors are still the most commonly used collectors in domestic hot water applications in warmer climates due to their affordability and reasonably easy installation. The collectors should last well over 20 years and can handle an operating temperature up to 80 degrees.

Flat Panel HWS

Evacuated Tube Solar Collectors

Evacuated tube collectors consist of glass tubes with a layer of heat absorbent coating inside them. As the tubes encasing the water pipes are a vacuum it greatly reduces heat loss. The thermal energy retention can be up to 97%. Copper pipes run through the centre of these evacuated glass tubes in a U-shape. These are all connected to a common manifold which is then connected to a slow flow circulation pump which pumps water to a storage tank below. The hot water can be used at night or the next day due to the insulation of the tank. Evacuated tubes are often used in commercial applications or in applications where hotter water is needed, since they are capable of generating temperatures above the boiling point of water (for example on dairy farms). While evacuated tubes have a long life similar to flat plate collectors, they are composed of fragile glass tubes which may occasionally need replacement.

Evacuated Tube HWS

Comparisons

As pointed out in Part One of this blog it is not a simple matter of using evacuated tubes or flat panels as each circumstance is different. Each collector design has its own merits. Both systems can save over 3 tonnes of GHG emissions per year and can reduce heating energy consumption in a home between 50%  to 80% especially when electric hot water storage systems are being replaced. In addition both systems can be up to 70% efficient when heating water and heat losses in the system are taken into account. So instead we should look at the benefits and the short comings of each system.

Evacuated Tubes

Advantages

• No heat losses due to convection and conduction because glass collectors are hermetically sealed.
• No change of performance during the service life of the collectors as there is no corrosion.
• Thermal diode operation principle, the hot water flows one way only from the collector to the tank and never the other way around.
• It is able to harness sunshine from all directions due to its cylinder-shaped glass tubes.
• Well-suited for colder climates with reduced hours of sunshine, where frost may be a problem or where the roof is prone to overcast from clouds.
• Freeze free so can be used in sub-zero temperatures and in the presence of snow.
• Easy installation due to light weight and no maintenance needed afterwards.
• Requires smaller roof area for installation.
• It is less apparent on roof because of the absence of a water tank coupled to it.
• Each glass tube is independent from each other so in case of breakage it can be replaced.
• Minimum greenhouse emissions when combined with gas boosting.
• Saves about 3 tonnes of CO2 annually when compared to electric storage.
• Very low running cost when used with gas or off peak electricity.
• On average it is about 5 years payback on investment.
• Suited for commercial and industrial applications.

Disadvantages

• Expensive to purchase due to more components, such as pump, separate water tank and associated plumbing and electrical work.
• Less cost effective than flat panels based on initial investment.
• Glass tubes could break easily in a hail storm or from falling branches.
• In higher ambient temperatures it is less efficient than flat panels.
• In direct summer sun it could be too efficient making the water too hot which results in wastage.
• Evacuated tube collector’s aperture area is typically between 60 and 70% of the gross collector area (meaning that’s how much of the total area exposed to sun is doing useful work).
• Some heat pipes are prone to cracking rendering the system useless especially at the braising points. These don’t like repeated heating and cooling down especially if it is very sudden.
• The welding should be done with silver alloys to prevent this from happening.
• Mainly made in China, thus not supporting Australia.

Flat Panels

Advantages

• Operates extremely efficiently in warmer climates and in higher ambient temperatures especially when water tank is horizontal and adjacent to the collectors.
• It can be between 44% to 76% more cost effective in warm climates than evacuated tubes.
• Losses are minimised because of water tank being located next to collectors.
• Thermosiphon operation minimises maintenance - no moving parts or distant pipes.
• Simple to install as system can be purchased as one unit with collectors and tank together.
• Affordable to purchase for the above reasons and because of less plumbing involved.
• No electrical installation required in most cases where stand alone system is used (ie the tank is not separate from the collectors).
• Space saving as water tank is located on roof and not in or around the house.
• Robust construction.
• Large collector area.
• Flat plate collector’s aperture area is typically between 90 and 95% of the gross collector area.
• Mostly made in Australia for Australian conditions, which supports the local industry and economy.

Disadvantages

• Can corrode.
• The air gap between the absorber and cover pane could result in heat losses during cold and windy days.
• It can rob the water of built up heat if the collector becomes colder than the water temperature.
• No internal method of limiting heat build up and have to use outside tempering devices.
• In colder climates it may need extra protecting devices from frost or freezing.
• It is more reliant on accurate northern exposure in order to operate efficiently.
• Installation could be difficult due to weight and size.
• Circulates water inside insulated areas. Prone to leakage, corrosion and restriction of flow due to possible airlock.

The graph below compares the three main types of solar hot water systems and their efficiency.

Solar Collector Efficiency Graph

Explanation: Solar collector efficiency is plotted as a straight line against the parameter (Tc-Ta)/I, where Tc is the collector inlet temperature (in °C), Ta is the ambient air temperature (in °C), and I is the intensity of the solar radiation (W/sq. m.). Notice that inexpensive, unglazed collectors are very efficient at low ambient temperatures, but efficiency drops off very quickly as temperature increases. They offer the best performance for low temperature applications, but glazed collectors are required to efficiently achieve higher temperatures.

Summary

From the above descriptions and considering the merits and drawbacks of each system the following conclusion can be drawn. In warmer climates and most temperate zones, where there is good exposure to sunshine throughout the year, and the ambient temperature is fairly stable the flat panel collectors are recommended to be used. Also, if there is good uninterrupted northern exposure available the flat panel is more economic. The flat panel is extremely efficient and the systems can produce sufficient hot water for most households. The use of a flat panel system will result in up to 80% reduction of hot water cost when compared to electric storage units. These are also more affordable with a faster payback period on investment. They are designed and made in Australia for Australian conditions.

On the other hand the evacuated tube systems have an advantage of being able to operate in colder climates or where there isn’t enough sun light (ie. some alpine or mountain areas, prone to overcast or where there are more trees). These systems also work well in the presence of snow or sub-zero temperatures. The unique design of the glass tubes allows it to capture sunlight from various angles thus heating the water for longer periods. In some cases where very high water temperatures are required - even in warmer climates- the evacuated tubes have the ability to produce water at higher temperatures than flat panels. Being smaller in surface area these units could be more suitable where there is a lack of space. Again 80% reduction in hot water cost and GHG emissions are quite achievable from such a system.

Please take note of the references for the graphs and information in this article. Where possible we have used information stemming from government websites, academic resources, and manufacturers data. If you need more information or actual references please contact us.

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.

(Part One)

One of the most energy intensive (and therefore costly) processes in any house is the heating of water. Heating water accounts to about 37% - 40% of the annual energy consumption in an average Australian household and about 20% of its greenhouse emissions. Therefore it is important to consider all the alternatives, such as using the heat of the sun in solar hot water systems.

The diagram below summarises the GHG emissions of each type of hot water system.

GHG emissions from hot water systems

Throughout the day, a sensor monitors the difference in water temperature between the water in the storage tank and the water in the collector (typically mounted on the roof). At a preset temperature difference, the sensor triggers a pump to circulate the water through the collectors where it absorbs solar heat.

Below is a summary of the two types of commonly used domestic solar hot water systems. Both the flat panel and evacuated systems have several versions, where gas or electricity is used to boost the water temperature if it is not sufficiently hot coming out of the water tank. In most cases the sun is simply used to ‘preheat’ the water to higher temperatures (40-70 C) before it goes into a storage tank. A pump may be used to circulate the water from the tank to the collectors until it is used. In addition the flat panel systems may use a heat-exchange mechanism typically where the water may freeze.

Flat panel or evacuated tubes?

In recent years evacuated tubes have become more popular and affordable and together with the flat panels have become widely used in Australia, especially since generous government rebates have been introduced. However, it is still disputed which system is better than the other. Obviously the manufacturers of each type of system claim that theirs is better than the other (sometimes claiming 90% to 160% more efficiency than the other system). The following reasons have been cited: because it captures sunlight better, is better in certain climates, is more cost effective, has better output for dollar spent, has faster payback, is less prone to failure or damage, is cheaper to repair, requires less roof installation area, etc.

It is difficult to find impartial opinions on the subject. It seems that each system should be examined in its own context. The climatic conditions and application will determine the better collector. One of them may be the preferred choice over the other due to a number of variables, such as the environment, availability of sunlight, elevation, orientation, average outdoor temperature, greenhouse gas savings, ease of installation including existing plumbing, payback period, running cost, availability of natural gas to use for boosting water temperature, how well the hot water tanks are insulated and many other factors. So which one is better and how do they compare?

To be continued……..soon……….