Energy Savings by Dave Savage

Building Automation Systems (BAS) have the ability not only to save energybut to also increase the comfort of the working environment which canimprove productivity.

Energy conservation is vital to the objectives set out by the G5 meetings andthe targets set for global reduction of greenhouse gasses caused bycontinued demand for energy usage, can only be met by a concertedapproach by all.

Many corporations have defined their internal “Green” strategies whichinclude the recycling of materials, defined reductions in emissions of harmfulproducts caused by production processes, and the provision of HVAC.

Satchwell Control Systems Limited, …(Elixir to provide intro)..one of the main areas for potential savings and comfort control is theoptimisation of the BAS.

The optimisation of the BAS is dependant on the physical plant, operator andthe type of environment that the BAS is being applied to.

Optimisation of the BAS equates to good energy management which is acontinuos cycle of activity, applied in order to ensure savings are beingmade. A regular review of plant operation must take place and further tuningapplied when necessary where identified.

Ease of use is fundamental with this approach to encourage the tuning ofdaily changing parameters. Operator time saving can be substantial also. Asimplistic approach increases user confidence and allows savings to beimmediate by even the most ardent of Ludites.

One measure of ease of use is the number of keystrokes / stages to modify aparameter, more than 3 to get to the parameter screen for changes wouldequate as being difficult and would discourage opportunistic changes beingmade which could equate to substantial savings not being made.

Areas for energy savings are as follows;

Set-points

The easiest way make savings is to reappraise and /or relax set-points.Caution must be applied as the changes need to be made in accordance withthe overall plant scheme as the settings may be crucial part of an overallcontrol strategy.

A shift can be applied in accordance with external conditions for example withan air conditioned plant the summer set-point for cooling can be increasedrelative to an increased external temperature (within a pre defined band).

A regular review of set points and modification is an essential part of theongoing energy cycle and must be continually reviewed looking for scope forfurther savings.

When an opportunity for set-point saving has been identified, by makingminor set-points changes over a period of time ensures a smooth transition,for example a stepped change of 0.5’C at a time for room temperature.

Shifting / relaxing set points in line with a combination of external conditionsand calendar can typically equate to 5-30% savings.

A set point reduction could equate to as much as 10% saving per ‘C on yourheating fuel bill and potentially higher with cooling / chiller plant.

Occupancy times

Time Schedule

Only running plant when the space is occupied is the greatest energy savingmeasure.One example is the occupancy pattern of a building such as an educationalestablishment which is continually changing due to activities such as nighttime educational use and school plays etc. It would be easy to apply a “carteblanche” approach setting a broad range time pattern but this would equateto periods of heating / cooling when not necessary. Regular reviews ofoccupancy would highlight that it may be possible to apply multiple switchingperiods of occupancy on different days

Typical time schedule which indicates a variable switch pattern.

In addition to a permanent change, the ability to extend a time operation on aone shot basis ensures that a one off change in occupancy such as latemeeting occupancy patterns are changed for that one period then reverting tothe normal occupancy pattern.

Calendar Schedules

BMS systems offer the ability to use different switching patterns on differentcalendar dates. This enables varied time scheduling to match varying workingpatterns to be programmed well in advance. This facility can be appliedwhere area occupancy is constantly changing week on week such asexhibition halls or meeting rooms. A saving is also made on operator time asthis can be configured once as oppose to having to make changes on aweekly basis.

Calendar schedule using different time switch patterns on different calendar dates

Relative Schedules

With this approach it is possible to have a single time schedule or “Coreschedule” controlling an entire site with other time programmes all referencedto it. The reference schedules will switch in empathy to the core schedule,some may switch before or after the core schedule. Modifying the coreschedule will automatically amend all other schedules ensuring all plant canbenefit from reduction in overall site working hours.

Holiday schedules

Holiday schedules are used in conjunction with time schedules ensuring thatno plant operates when there are holidays. The ease of set-up is againimportant as this facility must be utilised to take advantage of the 8 publicholidays in the UK for example. If this is equated to the potential of 52 weeksmultiplied by 5 working days = 260 an 8 day saving equates to over 3%possible energy usage.

Where there is an integrated systems approach on a site for example thelighting control system and chiller system are integrated to the BAS, a singlechange to a core schedule or holiday schedule can propagate to allintegrated systems ensuring HVAC systems work in empathy with the actualrequired occupancy and therefore maximise on energy saving potential byoverall site.

Site holiday programme

Optimisers

Prior the introduction of optimisers in the mid seventies, many buildings werecontrolled entirely by a mechanical time clock. These were often set to switchthe plant on at a time which often assumed the worst condition such as aspell of Siberian weather, a condition that may only occur 2-3 days perannum. This in real terms equated to plant being enabled in the early hoursof the morning till the late evening for every other day, without change.

The buzzword of the time was energy savings and synonymous with that wasthe word “Optimiser”. This was a stand alone controller which had an outsidetemperature sensor located on a north wall and a single internal temperaturesensor. A rate of temperature rise was calculated in accordance with howcold it was outside and the internal sensor. Based on this the plant wasswitched on at a time prior to the required occupancy time which equated toputting in the “Optimal” amount of energy.

Optimiser principle

The enhancement of optimisers in the early 1980’s introduced the optimumoff function which worked the opposite way. It predicted the off time based on

the external temperature and the room temperature, the earliest possible timethe building could have its heating plant switched off, whilst still retainingcomfort conditions.

Optimisers can provide typical savings of 5-25%, potentially higher withcooling / chiller plant, of energy usage compared with standard controllers.

The principle of optimisation is different today with a choice of algorithmssuch as a linear relationship between rate of rise and internal temperatureand logarithmic. Defined by the Building Research Establishment logarithmicthis can offer a potential 8% further saving on the energy used during thepreheat period by more accurate calculations of start time.

With BAS systems it is also possible to apply optimisation to cooling plant.Optimisers work the opposite way to the heating optimiser i.e. based on howhot it is and how high the internal temperature is the cooling plant will beswitched on at the latest possible time. The modern optimiser can determinewhether to initiate either a heating optimised start or a cooling optimised startensuring plant operates for the minimum time and results in savings. Theoptimiser adapts itself to suit the building and stores the perfect values foryour building.

The extensive information reports produced by the BAS on the optimisersoperation must be regularly reviewed to ensure the maximum savings aremade. This can be done after different external temperature conditions andon different days of the week. The BAS optimiser has additional “boost”functions which may be applied after the internal temperature did not reachoccupancy in the previous 24hours such as a Monday morning. This isenabled automatically to ensure comfort levels are achieved.

Frost protection

It is fundamental that during all times when the plant is switched off that afrost protection strategy is in place. A three stage frost protection strategy is arecognised approach and also has a benefit of saving energy as it is onlyapplies a heat source in the event of the water in the veins of the HVAC plantfalling below a specific temperature and the external / space temperaturesbeing below pre-set values.

Plant over-rides

We have discussed setting the occupancy pattern, during this time the plantwill operate to maintain heating / cooling within the building. Due to factorswhich influence the energy required it may be possible to operate the plant ina different mode or switch it off entirely. It is important that where optimisersare utilised that self adaption is inhibited during manual overrides andfailures.

Where plant is occasionally manually over-ridden, a regular plant review toidentify these plants set to a temporary condition is essential to ensure noenergy is used unnecessarily.

Compensation

With a wet system i.e. radiators, compensation is normally applied wherebythe temperature in the circuit varies in accordance with the externaltemperature, the colder it is outside the higher the water temperature in thecircuit is. There are minimum and maximum settings applied. This must bereviewed regularly or after any plant overhaul to ensure the compensationparameters are still representative and prevent over heating which will havean effect on energy consumption saving typically 5-15%.

Compensation graph

Standard compensation can be enhanced by the addition of room influence,solar influence and wind influence whereby a number of sensors are fed backinto the control loop and influence the set point, this provides increasedcomfort conditions an prevents overheating.

It is important to ensure that the maximum flow temperature for your systemis achieved / maintained for any boost period to ensure the quickestconsistent run-up.

Outside high limit

A wet heating system, even with compensation applied, can be switched off inthe event of the external temperature exceeding a pre-set as the ∆t(temperature difference) between internal and external is minimal or evennegative (Q=U A ∆t).no heating is normally required in a building when theexternal temperature exceeds 15 -20’C dependant on building type. It isimportant that hysterisis is applied to prevent plant switching in and out with aminor temperature change. Each building is different and this figure can becalculated accordingly.

The inverse of this can be applied with cooling plant to ensure free cooling isused when the external temperature is below a pre-set by closing a cooling

valve, zone, or disabling primary chilled water plant (See enthalpy controllater)

Disabling Humidification plant.

Providing the external conditions contain a moisture content above therequired level in Kg/Kg and satisfactory humidity levels are achieved in thereturn duct then humidification plant can often be disabled. The application ofthis must be reviewed on an AHU by AHU basis to ensure the control schemewill allow this as some plant types rely on 100% saturated air to reheat tosupply at the desired level.

Research has shown that enthalpy control implementation can provideenergy savings. Additional savings can also be made by reducing ventilationrates.

Zoning

A cost effective way of saving additional energy is to apply further zoning ofareas where there are different occupancy patterns. These zoned areas areonly heated / cooled when required. Each zone can have occupancy times /compensation / optimisation etc. applied to maximise the savings potential.

One consideration could be the location of people and equipment and theconsideration of relocation to zones where heating / cooling can be applied tomatch the working pattern.

Plant control stability

Plant that is not providing stable control can equate to extra energy usage(typically 3-5%) as well as increasing wear and tear on plant equipment.

Primary heating and chilled plant water must provide a stable source for otherplant such as central Air Handling plants supplying to further heating /coolingsources. Unstable control can occur due to plant performances / efficiencieschanging one example is a filter becoming blocked reducing air flow.

Unstable primary plant and/or control loop settings could cause AHU’scontrolled from supply air with heating and cooling to hunt. Control responsecan produce too much heating followed by too much cooling. This “fighting”cycle may only equate to a slight +/- variation round the set point, but inmechanical wear and energy terms this is inefficient.

By physically watching the control items for movement, using a dynamic viewof the plant, will highlight and assist in the fine tuning of the control loop tomaximise savings.

Log data showing unstable control

As part of any routine plant maintenance this process should be employedand corrective measures taken.

The quicker the plant reacts and stabilises the greater the savings.

Air handling plant

Most AHU plants consist of a supply and extract with a re-circulation duct withdampers on each to re-circulate the already heated / conditioned return air orto utilise whenever possible fresh air as a free cooling source.

A percentage of fresh air into the building is usually at a fixed percentage(typically 20%). By using an air quality sensor in the return duct. Thepercentage of fresh air can be reduced when air quality is good which willnormally be at the beginning of a working day, equating to a saving orincrease the percentage fresh air as necessary improving the workspaceenvironment.

Variable air volume plants need to maintain air by volume which can be usedin conjunction with air quality.

Enthalpy Control

Enthalpy is the total heat content of air.

Psychometric Chart

This can applied to AHU plant with heating and cooling. The principle is thateven though the outside air may be hotter than the return air, if there is lesstotal heat in the outside air it is more economical to utilise the “warmer”outside air than the return for cooling the air into the space.

Night Purge / Summer pre cooling

At the times of the year where daytime temperature is at a level where acooling load at start of building occupancy is required and the external air iscooler than the required occupancy temperature Night Purge can be applied.

This sequence enables central AHU plants to run in full fresh air mode for aperiod of time (30 minutes is typical). This purges the building with freshcooler air and reduces the initial load on the primary plant at occupancy start.This has the additional benefit of a fresh air feeling for the staff at occupancy.

Electricity Savings

Load cycling

Load cycling is the switching off of an electrical load for a period of time on aregular basis. This can be applied to background plant such as a fan or pumpwhere the effect of it being turned off will not result in consequentialinconvenience.

Load cycling should be overridden In the event of conditions exceeding a pre-set such as a low space temperature.

The savings in electricity made result in the time the plant is able to be off forexample within a 20 minute period if the plant can be switched off for 5minutes then the saving per hour would be 20 minutes or 25%. When appliedtypically this can result in 5-25% savings on the electricity bill depending onthe sizing of the plant.

Load cycling application

Disadvantages of load cycling are that regularly starting and stopping plantmay cause an increase in electrical load during start up or decrease theoverall life of the plant.

Maximum demand

Maximum demand (M.D.) is applied to buildings where a limit is set for themaximum consumption allowed (normally over a half hour period) and is acost reduction measure by preventing this limit being exceeded.

There could be 48 different limits per day and each day having a differentpattern.

If any one limit is exceeded then a “penalty” is applied to the electricity billwhich could equate to paying a higher tariff per KW/H consumed. The aim istherefore to ensure that the M.D. limit is not exceeded. Cost reductionassociated with maximum demand implementation are typically 3-5%

An outstation is synchronised with the M.D. meter and forecasts whether thelimit will be exceeded by monitoring the rate that electricity is consumed,versus the amount of remaining energy and time.

The algorithm associated with M.D. is complicated, but the net result is thatelectrical loads, site wide, are shed if the forecast predicts the limit will beexceeded. They are reinstated after the danger period has passed.

The demand target can be calculated by the BAS if required to further reduceconsumption.

Maximum demand application

Loads are shed in rotation per priority level and a matrix enables the choiceof criticality of load. The rate at which they are shed and restored iscontinually reviewed by the calculations.

The complication with M.D. is which electrical loads can be shed. The lowestlevel may be electrical water heaters, the highest level may be one of anumber of chillers whereby it may be out of sequence for a period of time as itgoes through an shutdown sequence before it is reintroduced to the controlscheme.

Indirect reduction of maximum demand could be applied by overriding theamount that a chilled water control valve can open to.

This would indirectly reduce load to the chilled water plant and thereforereduce electricity consumption however the time in which the valve takes todo so may not be practical, but may be possible on parallel routines.

The intelligent office approach

The demand for intelligent integrated solutions within the building wheresystems such as access control, chillers, lighting etc. are connected to theBAS system is increasing.This approach provides one coherent system and has the advantages of asingle user interface which can be customised per user, reduced training,standardised presentation of alarms and logged data to name a few.

This brings further opportunities for energy savings by applying a controlstrategy where the plants work in empathy with each other.

Intelligent integrated systems showing typical services connected to a BAS

One example could be where the user uses the access control to gain entryto a building, this signal is used by the lighting control and HVAC systems togo from economy relaxed levels of lighting and settings to an occupied mode.

To equate this to a % saving is difficult but if only half an hour per daysavings will soon accumulate over a short period of time.

Monitoring and Targeting

Monitoring and targeting such as Satchwell Montage is a powerful new way tosave money on utilities and other raw materials. By using metered datagathered from the BAS system, and providing some additional production,weather data or other load data and saving of 5-25% of your utility costs canbe made with little or no capital expenditure!

The techniques of cost reduction, called Monitoring and Targeting or M&T,employed have been proven to consistently deliver this level of savings in ahuge range of organisations. The evidence comes from countless M&T casestudies produced by the UK Energy Efficiency Office, World Bank and EECDirectorates.

In fact the process is very simple. In the software you compare your utilitycosts with the Influencing Factors that determine that cost. SatchwellMontage tells you clearly when you have done well as well as when you could

do better. Consider the graph below. It shows the oil used by a boiler againstthe external temperature (using degree days), over a week. As you can see,there is a significant degree of variation in the amount of oil used for roughlysimilar heating needs - the savings come from identifying when performancehas been good or poor and changing behaviour or control to repeatefficiencies.

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Colder Weather ->

Oil Used

The points below the dotted line show better than average performance! Those above are worse than average.Clearly there is lots of room for savings if only you can see where you are…

By providing an “overview” of your performance - typically weekly - M&Tcomplements the real-time, alarm and controls facilities of the BASsoftware as detailed above. Importantly, it extends the benefits by givingadditional perspectives of the site - performance, costs by department ortenant, long-term trends, savings achieved through investments etc.

Monitoring and targeting active summary display and drill down graphs

Satchwell Montage’s powerful reporting and analysis tools let you achievemany different objectives, from producing invoices to determining ranks ofimprovement and calculating ratios such as energy use per m2.

With an unlimited user license on one network - you can spread thebenefits of this tool to a large number of people in your organisationallowing the share of information and data.

Satchwell Montage has a full suite of report and graph design tools it alsointegrates with other Windows applications, enabling the export of data toa wide range of file types or to copy and paste graphs and other outputs.In addition to receiving data from the BAS system, values can be enteredmanually, with a hand-held data logger and even picked up from other datacollection systems. All of this means that there is complete flexibility tomeet the needs of many different types of end-users.

Tools, such as this, help address the needs for energy and environmentalimprovements. Improvements that are so clearly demanded bygovernments and public alike. It demonstrates Satchwell Control SystemsLimited commitment to remain at the forefront of technical innovation andto provide the “best of breed” tools to maximise the benefits of ourcustomers systems.