Comment on energy efficiency of air curtains

By Steve Brown, Development Director, Envirotec

A common misconception regarding the use of door curtains in retail environments is that they always use large amounts of energy. This does not have to be the case.

The most important aspect of an air curtain is the barrier of air it creates between the external and internal environments and not its heat output. I will explain why this is important.

No Air Curtain

Warm air naturally rises and when a heated space is subjected to a lower temperature, such as when a door is opened, the warm internal air rushes to escape out of the top of the doorway. This escape of warm air is made up by cold air rushing in at the bottom of the entrance effectively lowering the temperature of the heated space.

The main aim of an air curtain is to reduce this effect by forcing the escaping warm air downwards and back in to the heated space thus reducing the cooling effect of cold air ingress.

A correctly specified air curtain will help improve energy efficiency, compared to doors that are continually opening and exposing the interior of the shop to outside temperatures.

An air curtain creates a barrier that helps prevent the cold outside air from mixing with the warm indoor air. Air curtains with intelligent controls can be configured to contribute to the heating of the interior of the shop, so the energy consumption of the main heating system could be reduced in proportion to the energy consumed by the air curtain.

Air Curtain Fitted

A crucial factor here is that the air curtain should be correctly specified for the doorway it is protecting, with the span of the warm air jet being wider than the doorway. It is also worth noting that many air curtains now use low carbon, low energy heat sources such as heat pumps, thus improving energy efficiency even more.

Air Curtain with heat pump 

The same principles apply to shops that are air conditioned in the summer, as an air curtain will prevent the cooled air from inside the shop being wasted through the doorway.

Closed doors, with no additional protection, which are constantly being opened during periods of high footfall, actually reduce energy efficiency due to the conditioned air leaving the building as explained above.

Therefore, the ideal solution for balancing the requirements of access and energy efficiency is to operate a closed door policy with an integrated correctly specified air curtain, using an efficient heat source, which becomes active when the door is opened.

Sales Engineers and Sales Agents Opportunities in High Wycombe, Bucks

HVAC Sales Engineers and Sales Agents required by leading HVAC equipment and services provider.

Envirotec’s Energy efficient Air Curtains and bespoke design Air Handlers have been industry benchmark products for over 40 years.

Increased demand for sales support for Envirotec’s existing products, services and exiting new products has led to the following position being created:

Sales positions include:

• 2 Internal Trainee Sales Support Engineers based in Envirotec’s head office in High Wycombe, Bucks.
• Sales Engineer to cover London area
• Sales Engineer to cover East Midlands area
• Sales Engineer to cover Manchester area
• Sales Agent to cover Newcastle and North East area

To express your interest or to find out more information please contact:

Peter Faruqi - Sales Manager peterfaruqi@envirotec.co.uk  M: 07795 494 884 or

Steve Brown – Development Director stevebrown@envirotec.co.uk  M: 07917 185 630

How a Good Control Strategy Saves Energy and Money

Enetec Energy Saving Intelligent Controllers

Envirotec have been supplying quality heating and ventilation related products to the HVAC trade for over thirty-five years. During that time the company has developed into one of the market leaders as a manufacturer and innovator of warm air door curtains. Supplying products for a wide variety of commercial applications Envirotec have produced around 100,000 door curtains since it entered the market-place in the late sixties.

“A door curtain as part of a heating system is an energy efficient device”.

The principle of a door curtain in its most powerful form is to separate the internal and external environments. This is achieved by creating a barrier of air across a doorway or entrance.

Door curtains create an invisible screen helping to prevent the ingress of flying insects, pollen and fumes. Conditions inside buildings are improved and cold zones adjacent to entrances can be minimised.

Less powerful door curtains or over door heaters, help condition air that enters through entrance doorways.

An added benefit to the building occupiers is the saving in energy required to heat or cool the building because less of the conditioned air leaks out of the building.

Enetec is a purpose built designed control system which maintains tight control of space temperature. The heating elements are burst fired with electricity to optimise their power consumption allowing the output to be proportionally controlled, supplying the exact amount of energy required to maintain space temperature

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Building management system or stand alone control

The Enetec family of energy efficient door curtain controllers are configured either as a “stand alone system” or for control via a “Building management System” (BMS).

The on board computer can be configured to achieve optimum energy efficiency whilst maintaining comfort conditions. This allows facility engineers and M&E engineers the flexibility required to run today’s modern buildings.

The “plug-n-play” style of Enetec should be appreciated by facility engineers as it arrives factory set. All that is required are BMS enable and analog signals to give a high degree of controllability.

Master and Slave options save additional site wiring - negating the need to supply BMS interface connections to multiple banks of door curtains. One master unit can control up to sixteen slave units via a communication interface (RS485). Connection cables supplied (2m long supplied as standard) make for easy site connections.

Each slave unit is pre programmed to run with default settings so that in the event of a BMS or master unit failure the slave unit continue to run.

Benefits

·         Accurate temperature control using a closed loop control process.

·         Energy saving by maximising usage of latent heat stored in the elements reducing energy consumption by up to 60% when compared to a traditional thermostat control system.

·         Does away with the need to have energy hungry auto opening or revolving doors.

·         Allows the premises doors to be permanently open during opening hours.

·         Integration with Building Management Systems (BMS) allowing optimum efficient control.

·         Can be retro fitted to other electric/water heaters.

·         Buildings without a BMS or time clock system can use the features to accurately control the on and off periods of the warm air heaters, helping to avoid unnecessary operation.

·         Additional control equipment not required.

·         Master and slave options for multiple banks of door curtains.

Features

·         Up to a maximum of 28 time settings can be programmed.

·         Fan speeds automatically controlled for optimum efficiency.

·         Fan speeds can be pre-set to a fixed speed if site conditions require.

·         BMS on/off control/fire interlinks.

·         BMS set point control via 0-10V/4-20mA input.

·         BMS duty cycle control via 0-10V/4-20mA input.

·         BMS fan speed control via 0-10V/4-20mA input.

·         Pre-programmable set point parameters.

·         Optional IR receiver for infrared remote control.

·         RS485 port for easy connection to a wall mounted control switch reducing the amount of time and materials required for site installation which also can be used for slaving other units.

·         RS232 communication port for direct connection to a PC to modify or reset parameters.

·         Real time clock and configuration data stored in non-volatile memory with long life (10 years) lithium manganese battery backup.

·         Analogue inputs providing calibrated range (-10 to +30°C) thermistor inputs to enable accurate temperature zone measurement

·         Digital inputs, six opto-isolated, suitable for volts free contacts, thermal cut outs, pulse inputs energy monitoring etc.

·         Fan failure sensing enables automatic shutdown of electric elements in the event of a fan failure. Volts free contact relay linked to fan failure for fault indication.

·         Heater failure sensing via current transducers with a volts free contact relay linked to heater failure for fault indication.

·         Simple to use menu for configuring the controller.

·         Single phase or three-phase control of heating elements using zero voltage switching burst fired triacs.

·         Heating load outputs up to 90kW

Temperature control explained:

Enetec is a closed loop control system. It can also be configured as an on/off open loop control if required.

A process control loop consists of a sensor to measure the temperature variable, a controller and a control device e.g. Contactor or thyrister drive.

A temperature controlled system is composed of four essential elements which all affect its performance:

1. The Load – the air that needs to be at determined temperature.

2. The Heat Source – the heater that provides heat to the load.

3. The Sensor – measuring the temperature of the load and feeding back the information to the controller.

4. The Controller - A device which controls the heat flow to the load by adjusting power output from the heat source according to the information received from the sensor.

 The Enetec controller will compare the temperature measured by the sensor with the desired load temperature (the Set-Point) and increase heater power if the sensed temperature is too low, or decrease power if the sensed temperature is too high. The heat source, the sensor and the controller form the control loop and together act upon the load.

The load temperature (or process temperature) is compared by the controller with the required value or set-point, set by the user. The enetec controller automatically adjusts the power to the heat source to achieve no error between process temperature and set-point.

The type of control action affects the performance achieved.

·         On/Off control - This is a simple form of control it takes little account of thermal time constants and simply switches the heater off or on as the process temperature passes through the set-point. This will usually result in continual oscillation around the set-point (hunting) due to the switching hysteresis. It is used where high accuracy isn’t needed, or for when a constant heat output is required.

·         Proportional plus Integral gain control - is used for high accuracy and energy efficient control of load. Proportioning control means that the controller recognises the size of the deviation from the set-point and adjusts the power output accordingly. This prevents oscillation around the set-point, and the integral parameter adds extra accuracy, with little or no offset or overshoot. The proportional and integral gain parameters can be adjusted (or tuned) by Envirotec engineers to give the optimum control for the particular conditions of the system.

With on/off control, the controlled heater can only be on or off, there is no setting in between and the size of the corrective action is unrelated to the temperature deviation. This leads to the oscillation described above.

In proportional control, the control action can be varied between 0 and 100% of the available heat source tailored to the size of the temperature deviation measured by the sensor. Where, for example, large amounts of cold air cool the system down (so that it needs rapid heat-up) a large injection of heat would lead to huge overshoot without proportioning action.

The width of the proportioning band is be set to just exceed the limits of any normal high or low temperature excursions in the system. If the proportional band is too narrow, oscillations resembling on/off control will occur; if too wide, control will be stable but sluggish, probably with an offset at equilibrium. The offset is corrected by biasing the proportional band so that the band is in the correct place once tuned.

An offset in the control temperature can be compensated by incorporating an integral parameter, which positions the proportional band for the correct power output to achieve equilibrium at set-point. (Proportional plus Integral control (PI)).

Setting the Proportional and Integral Gains

With the integral gain set to zero, the proportional gain is set to give the response shown in the diagram below. If the gain is set too low, the response of the heating system to changes in air temperature will be very slow. If the gain is set too high, an oscillatory response will occur which could take hours to stabilise. Once the optimum response has been achieved, then the integral gain setting is increased to minimise the offset that occurs with proportional action only.

Electric heater output control

The controller output is interfaced to the heat source by a switching device which contains Solid State Relay (triac) complete with a zero voltage crossover or synchronising drive circuit; it takes the form of a triac board and heat sink assembly having no moving parts to wear out.

Where continuously variable control is needed, a BMS linear voltage or current output can be used (0-10V or 4 - 20mA) this can be toggled between setpoint control and on/off duty cycle control via a digital input.

Water coil heater output control

When low temperature hot water (LTHW) is used as the heat source medium the Enetec controller can be programmed to control either a 24V raise/lower or 0 -10V type valve actuators.

The raise lower type valve will be driven to the correct position to allow only the precise amount of LTHW to flow to reach the required setpoint.

 The amount of time required to drive the valve fully open/shut will be programmed into the controller and this will be used to calculate the amount of travel time required to reach the flow rate needed to maintain the setpoint. Every 24 hours the onboard software automatically checks the valve position and will drives it fully open and shut. This is to make sure that no drift has taken place during the control period therefore maintaining accuracy.

The 0 -10V controlled valve actuator will be driven to the required position in a similar way to which the electric units are controlled by determining the duty cycle needed and converting the 0 -100% output into a 0 -10V signal on a linier scale. The valve will be opened and shut according to the demand therefore only allowing the required flow of LTHW.

If multiple door curtains are required to protect an entrance one Enetec controller could be used to control a shared valve saving time and money on installation and giving energy saving benefits.

Burst firing (Electric elements only)

This method provides variable electrical output power for the control of temperature. It is achieved by triggering the device on and off in multiples of complete mains cycles. The power to the heating load is switched on and off only as the mains cycle passes through zero Volts. This minimises the electrical noise sometimes associated with switching heating loads and greatly extending element life. The Enetec’s duty cycle is achieved by burst firing the heating load over a two second time cycle e.g. a 50% duty cycle equates to the elements being powered on for 1 second and then off for 1 second.

Thermistor Sensor

Thermistors (derived from thermally sensitive resistors) are solid state devices that exhibit a high coefficient of resistivity, used to measure temperature, their resistance changes proportionally to changes in temperature.

Energy Saving 

A project partnering Envirotec, a leading high street retailer and BSRIA compared methods of controlling an Envirotec air curtain at the entrance of a supermarket for a six week period resulted in significant energy savings being achieved.

The results showed that the Enetec control used significantly less power maintaining a return air of temperature of 24°C compared to traditional control methods.

Energy savings of between 30 – 60% are anticipated over a 12 month period resulting in a return on investment of between 12 and 24 months depending on usage, heating load size and the cost of a unit of energy.

For more information on energy saving contact Envirotec 

Air Handling Units (AHU's) Refurbish?

When to refurbish?

 There are many situations where refurbishing existing air handling plant is a more cost-effective option than replacing with new.

When it comes to establishing a sustainable policy and minimising environmental impact, energy efficiency generally dominates the headlines. And while this is clearly an important consideration there are other factors to consider as well.


In existing buildings, for example, there are often opportunities to refurbish major items of plant such as air handling units (AHUs), even those 20-30 years old, instead of replacing them. Not only does this reduce material consumption and embodied carbon, it also creates an opportunity to upgrade the performance of the plant while reducing costs and disruption.

To put this into perspective, consider a 2m x 2m x 6m AHU with an airflow of 7m3/s. It incorporates a volume control damper, bare tube frost coil (LPHW), panel filters to F4 efficiency, bag filters to G6, CHW cooling coil, LPHW reheat coil, fan and motors - and would cost £12,500 to supply and install, based on good access.

To refurbish a similar unit, replacing all internal components, treating any corrosion, replacing damaged external panels, re-commissioning and providing a 12 month warranty would cost £9,125 – a saving of 27%.

In fact, depending on circumstances and the level of experience and expertise applied to the project, the savings achieved by refurbishing will typically range from 20% to 50%. Furthermore, there will be additional life cycle cost savings through reduced maintenance costs and improved energy efficiency, all providing a fast return on investment. A recommissioned system and updated Operation & Maintenance manuals will also contribute to reduced cost of ownership.

Why refurbish?

There are many reasons to consider refurbishment, ranging from deterioration of components and casework through to a desire for higher performance and/or improved efficiency.

Clearly, all AHU components will suffer some age deterioration. Condensate mixed with airborne pollutants may cause corrosive oxidation of cooling coils, for example, There will also be wear and tear on moving parts in fans and motors, while static components may have years left in them.

For these reasons, an initial inspection to identify opportunities for refurbishment is the first stage in any such project; followed by a method statement, risk assessment and detailed costings.

Very often, it will also make sense to take the opportunity to improve performance. In such cases, existing components can be replaced with newer designs that comply with modern standards and specifications, while also offering improved efficiency. For example, it may be possible to replace original standard fans driven by AC motors with more efficient backward-curved fans and DC motors. Similarly, heat transfer across heating and cooling coils has improved in recent years, as has the efficiency of filters and the thermal and acoustic insulation of replacement AHU panels. The same principles are true of any direct expansion refrigeration equipment installed in the AHU.

Where a major upgrade to performance is required, or where major deterioration has occurred, it is also possible to replace whole sections or, indeed, introduce new sections. In such cases, if access is restricted, these may be taken to site and assembled in situ.

In fact, this highlights another major benefit of refurbishment, as there are many buildings where access to the AHU plant is very difficult, so that refurbishment becomes a much more sensible option. When planned properly, refurbishment is also less disruptive compared to a new installation as the work can be carried out in phases outside normal working areas. Also, units serving critical areas can be isolated so the work is phased to suit the needs of the building’s occupants.

Clearly, then, there are many good reasons to consider AHU refurbishment as an alternative to replacement. The key is to harness the expertise of specialist companies that have extensive practical experience of AHU refurbishment and can deliver a complete turnkey solution.