Green without eco-bling 07 June 2011

As energy saving climbs up plant engineers' agendas, Dr Tom Shelley reviews some of the good and not so good technologies for heating, ventilating and air conditioning

There are many cost effective ways to reduce energy consumptions in buildings, but don't expect a reasonable return from, for example, a wind turbine erected on a factory end gable in the middle of a commercial estate. This is an example of what is coming to be known as 'eco bling' – adornments that have more to do with being seen to be green than serving any useful purpose.

That's not to say all novel ideas concerning wind energy, photovoltaics etc don't work: many do. Sorting the wheat from the chaff is about applying a good dose of engineering circumspection. However, it is also worth noting that some of the best energy saving ideas for buildings and plant are simple and can also be relatively invisible.

Take thermal insulation. Most plant engineers are aware of the requirement to insulate walls and roofs but, sadly, fewer are aware of the importance of insulating cold pipes in refrigeration and air conditioning systems. German headquartered Armacell, which makes Armaflex foam insulation, recommends 15.5—25mm insulation for chilled water pipes and 32—50mm for refrigeration pipework. Installation costs are claimed to be recoverable after five to seven months and the company also calculates that for every cubic metre of its product, CO2 savings amount to1,150kg for air conditioning systems, 1,900kg for refrigeration systems with a line temperature of -5°C and 2,550kg for those operating at -36°C.

Another high impact way of improving the thermal behaviour of buildings with windows is to introduce blinds, whose behaviour can be greatly enhanced by modern coatings. Swedish Hammerglass EnergyBlinds use sputtered aluminium, which makes them highly reflective. Sunlight mostly consists of wavelengths from 100 to 2,500nm, of which the 350nm to 2,500nm portion makes it through window glass. Conventionally, when this light strikes inner surfaces, it is converted to infrared radiation in the range 10µm to 30µm, which heats the room – the well known greenhouse effect.

EnergyBlinds, however, transmit 10%, 15% or 40% of incoming light, according to type, but reflect the rest back through the glass unchanged. At night, they also reflect infrared radiation back into the room, reducing heat losses through windows by up to 30%.

On a different note, HVAC running costs can also be greatly reduced by employing variable speed drives, so that fans only run as required, not continuously at full speed. Schneider Electric's new ATV212 Altivar drive, for example, is designed specifically for HVAC. It's 'C-Less', meaning it does without large energy storage capacitors on the internal dc link, because it doesn't need to handle high over-torques. As a result, it produces 30% less harmonics than other drives. It also monitors flux within the motor and adjusts drive output to meet needs, further reducing energy consumption.

These drives are available from 0.75—75kW, are IP21 or IP55 rated and come embedded with Modbus, BacNET, Apogee and Metasys digital plant communications. A fire mode function works with motors used for smoke extraction and a damper control function ensures that the motor won't start unless dampers are in the correct position.

Optimised in a very similar way for the HVAC market are CFW700 and CFW701 drives from Weg. These too are less expensive than general purpose drives, because of reduced capacitance on the dc bus and less complex software – although they still include auto-configuration, PID control, overload and over-temperature protection.

Moving on, at the Hannover Fair in April, Econ Solutions demonstrated an energy monitoring and analysis system, which, according to project manager Marc Rostock, was developed for its parent company's operations. Based on brick sized electronic units that interface with sensors and are connected by Ethernet, it uses a web browser interface. He claims that, on average, installation of its system saves 25% energy costs within the first year.

A similar figure is cited by Ener-G Controls for its E-Magine building energy management system. Managing director Dr Cedric Rodrigues says the firm has tackled "two major system flaws" that prevent many BEMS from delivering their projected cost and carbon savings. First, the software is pre-configured to recognised CIBSE (Chartered Institute of Building Services) control strategy standards – so it avoids problems caused by inconsistent programming. "Customers benefit from control strategies that are repeatable and not reliant on an individual engineer's skills," he says'

Second, the system prevents the classic flaw of users adjusting settings and gradually eroding designed-in energy efficiency benefits. "E-Magine locks-in optimal settings, so that the BEMS achieves peak performance throughout its lifetime," says Rodrigues.

These are serious points. Lisa Wilkinson of energy logging specialist t-mac says: "Working with a couple of retailers, we have seen energy costs reduce phenomenally by limiting air conditioning setpoints so staff cannot abuse the system." Her company's systems also link air conditioning and heating to ensure they "don't fight each other", and she also alludes to sensing external temperature so that over-door heaters only trigger when needed.

Wilkinson describes switching HVAC equipment on and off according to time of day and business hours as Step One. Step Two, she says, is managing overall BEMS performance and adding in remote diagnostics and maintenance. "Finally we look to educate staff to ensure they are aware of the impact a change in system performance can have on the cost and carbon emissions of their business," she says.

Fleshing out the kinds of improvements that can be made, Cleeve Park School in Sidcup, Kent, is expecting £10,000 savings per annum, thanks to a Dedicated Engines (DEL) eFM Internet-based BEMS. The school has two plant rooms: Zone 1, the main boiler room, with three boilers; and Zone 2, with two boilers. Prior to installation of the new system, there was no centralised BEMS, and the boilers were operated independently, using timers and manual controls.

With eFM system installed, boiler run times in Zone 1 have been reduced from 96.5h to 40.75h per week, while Zone 2 went from 168h to 40.75h. "We are delighted with the results so far," states Don Blaylock, assistant head teacher. "We were looking for ways of reducing our energy costs, but were restricted by lack of funds. The NESS (National Energy Saving Service) Share programme not only solved the funding issue, but also recommended technologies. Now we are able to properly manage and control the operation of our heating and hot water through the eFM system resulting in significant savings."

But there is still more to solving building energy management than sorting out staff system abuse. David Hudson, senior product engineer with couplings manufacturer Victaulic, makes the point that HVAC system flows change over a typical 24 hour period. "Because of heat gain from the sun and changes in building occupancy, the demand for heating and cooling varies, not only throughout the day and night, but also by building sector," he reflects.

For him, one solution is balancing valves to ensure that heating and chilled water systems deliver correct flows to all terminal units in an HVAC circuit. In an unbalanced system, he explains, some building sectors will experience underflow or overflow conditions that impact indoor climate. For instance, areas closest to energy production and delivery might receive excess flow, resulting in excessive heating or cooling while remote areas remote receive insufficient flow.

Problems can result from poor design, improperly adjusted balancing valves, or clogged strainers and coils, he warns – and that can be expensive. Hudson claims that for every unnecessary single degree temperature above 20°C there is an 8% increase in heating costs, while for every single degree cooling below 23°C, there is a 15% increase in cooling costs.

Focuses the mind, doesn't it.

Dr Tom Shelley

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