ABSTRACT

Significant savings and operational return on investment can be realized by a building owner that utilizes his building automation system to control his landscape watering.  Most  buildings of recent construction or significant remodel, incorporate some form of building automation with distributed control networks for HVAC, lighting, other building systems and internet integration. 

A majority of these buildings also incorporate landscaping with some form of automatic irrigation or sprinklers.  Automatic sprinkler valves are usually 24vac activated by a multi-zone electronic clock.  Municipal outdoor watering regulations have become increasingly restrictive because of water management policies.  Automatic sprinkler clocks have been available for years from the irrigation industry that incorporate some water conservation features.  However the sophisticated systems are usually very expensive and reserved for irrigation of large areas such as golf courses, campuses and parks.

This paper discusses the issues of controlling the landscape irrigation with the building automation system. Water management and conservation features usually available only with very sophisticated landscape irrigation systems are easily implemented with building automation systems.  Technical issues are discussed along with a business case presented for the benefits to be realized by the BAS controlling the watering system.  

BUILDING LANDSCAPE IRRIGATION TUTORIAL

Being familiar with landscape irrigation systems will enable those in the HVAC industry to recognize and identify with those concepts presented in this paper.  Landscape irrigation is divided into two basic categories, those using the treated pressurized municipal water system and those using a secondary untreated irrigation water supply such as a canal that requires a pump to pressurize the irrigation lines.  Both the municipal systems and the pumped secondary systems usually tie into the water source at a single point that does not exceed 1 inch to 1 1/2 in diameter. This supply line is connected through an anti-syphon valve or backflow prevention valve for municipal water systems so that contaminated water in the irrigation lines may not syphon back into the treated city drinking water lines.  A pump sucking water through a strainer or filter pressurizes the lines and pumps water to the sprinkler heads in the secondary water system.  The underground irrigation lines are usually run in CPVC plastic and the irrigation system is zoned so that a defined number of sprinkler heads are piped to spray in parallel, delivering a predetermined gallonage of water for a landscape zone such as an area of lawn or shrubs with a similar watering need.   A zone is supplied by a single normally closed irrigation valve with a 24vac pilot solenoid that is energized by an irrigation clock to operate for a defined number of minutes a set number of watering cycles per week.  These zone valves usually have a bleed screw which allows the valve to be opened manually for sprinkler head testing without the need to energize the solenoid.  A flow adjustment knob limits the maximum flow that can pass through the valve.   From 1 to 4 of these zone valves are usually piped in a parallel manifold and located in a single underground box with a removable plastic lid at the ground surface.  These boxes are then distributed across the landscaping, all connected in parallel to the single water supply. 

The electronic irrigation clock may have as many 24 or more zones that start with zone 1 activated at a set time per week to water for an adjustable number of minutes. The next zones follow in sequence with an adjustable number of watering minutes per each zone.  The water supply lines are sized so that normally only one zone is watering at a time.  If a pump is used to pressurize the system then a pump start contact will energize the pump motor starter anytime any of the zone valves are energized.  More sophisticated clocks may allow for grouping a number of zones together to have different start times per week and a separate number of watering days per week. 

The wiring is run in 18 gauge or larger multi-conductor low voltage underground cable that is often directly buried with the irrigation lines rather than enclosed in plastic conduit.  The wiring terminations in the valve boxes are often wire nuts that are filled with grease to prevent electrical connection corrosion.  The valve boxes are often full of water during the watering times.  All of the sprinkler zones are "home-run" wired to the single irrigation clock which may result in some very large wiring bundles.  The irrigation clock is usually powered by a 24vac transformer that also powers the zone valves.  A landscape architect or irrigation system designer will size the sprinkler heads, lines and zones based on projected watering requirements for the landscape plants and lawn areas.

FEATURES ADDED TO THE IRRIGATION SYSTEM THAT PROVIDE MAXIMUM BENEFIT WITH BUILDING AUTOMATION CONTROL

BENEFITS OF A FLOW METER

Since the total irrigation system is usually connected to the water source at a single point, a single flow meter, with a pulse output, of the type usually used for municipal meter connections can be supplied and installed for several hundred dollars.  With the water flow reading available to the building automation system (BAS), there are a number of significant benefits that can be realized. 

1. When the irrigation system is first commissioned, having a flow reading per zone can significantly reduce the time required to adjust the watering flows.  Sprinkler zones are typically calibrated by relying on published flow rates per sprinkler head and then placing measuring containers to catch the water as it falls on the landscaping.  The zone must often be operated a number of times, with the commissioning person waiting through the whole watering cycle for each zone to collect the water in the container, adjust the valve flow rate and then try the zone again.  Often times the zones aren't calibrated because of the time required and so many areas are significantly over watered for the life of the building.  If the water is charged per gallon supplied by the municipality, this can be a significant lifetime cost.  Only under watered areas show up by the resulting brown spots in the vegetation or lawn.  Many municipalities have a sewer usage charge based on the gallons of water used.  Metered landscape water can be deducted from the sewer water quantity bill. 

2. Preparing a table of zones and actual flows per zone as read by the flow meter allows the BAS to be programmed to generate over-flow and under-flow alarms per each zone.  Usually problems are only identified weeks later when there is an area of lawn that is dying or turning brown from lack of watering.  An example would be an alarm generated by a "midnight geyser."  Landscaping crews frequently mow off sprinkler heads that don't fully retract.  When the zone is being watered at night, the lack of pressure drop from the missing sprinkler head allows most of the water to be wasted, shooting up in a geyser and the other heads on the zone broadcast only a small fraction of the normal water which causes dying lawn or brown spots over time.  Unless someone is present to witness the event, this condition can persist for weeks or months.  The author has observed missing sprinkler heads causing “midnight geyser” that generate an overflow  of  130 to 150% of normal.  The BAS would generate an alarm of an overflow, shut-off  the zone valve and  e-mail an alarm to the cell phone of a maintenance person, telling them which zone has a problem.   Calibration for this condition is easy, simply unscrew a sprinkler nozzle and record the resulting flow during a test of the zone.  "Hanging on" or sticking valves that continue to water when the next zone is activated will also generate an overflow alarm.  An underflow alarm would also be generated by a valve that fails to open.  A partial opening valve would also be detected and an alarm generated.  A significant overflow could indicate a broken line.  If flow occurred when no zone valves were activated, possibly indicating a broken pipe, then besides generating an alarm, a main shutoff valve could be energized.  If there is a significant underflow on a pumped system, automatically shutting off the pump in addition to generating an alarm, would prevent the frequent pump motor burnout problem that occurs due to leaves plugging filters or canal inlet strainers etc.  If there is considerably variable supply pressure from a municipal water system, it may be necessary to add a pressure sensor to the inlet of the flow meter and use the pressure measurement to offset the “midnight geyser” flow alarm settings per zone.

3. If the BAS is programmed with the area square footage of each landscape zone, watering the zone with a predetermined precipitation rate is possible by using the feedback from the flow meter.  While a zone is being watered, the flow meter is providing a gallon per minute water usage signal. When the required amount of precipitation is reached during the watering cycle as determined by the total flow delivered to the zone, (from the flow meter signal), the zone valve is shut off and the watering cycle advances to the next zone in the sequence.  One inch of precipitation over a square foot of area is approximately 2/3 of a gallon. If the amount of precipitation needed to water a lawn, as published by the municipal water district using weather data and weather forecasting is 1.5 inches of precipitation per week, for example, one gallon per square foot per week would equal the precipitation requirement for the lawn.  If  the area of the zone being watered is 300 square feet, and the water delivery is 10 gallons per minute then as soon as 300 gallons, (30 minutes of watering time)  is reached then the precipitation requirement is met.  Rain fall precipitation measured automatically could be subtracted from the watering requirements.

BENEFITS OF USING AN OUTDOOR AIR TEMPERATURE SENSOR

Most building automation systems already have an outdoor air temperature sensor.  Outdoor air temperature is only one principal factor to predict soil moisture evaporation in determining watering needs.  Adding a solar intensity sensor signal to the equation with outdoor air temperature more accurately reflects the landscape watering needs.  Analog output pyrometers are available but a simple photovoltaic cell puts out a dc current that is directly proportional to solar intensity.  Measuring this current as a percentage of the total current output in bright sunlight and averaging it with the outdoor temperature as a percentage between 50F and the highest possible, the BAS can then adjust watering minutes per zone to reflect the actual need.  During the highest heat demand the watering time can be increased to 120% whereas during cloudy cool days the watering times can be decreased by 50% or more.  Summing the temperature/solar effect from 10am to 4pm daily and maintaining a sliding average over 5 days, dropping the oldest day, provides a reliable factor to influence watering times. An outdoor air relative humidity sensor could also be used to influence the solar intensity and outdoor temperature equation.  Using soil moisture sensors, installed over a number of sites in the landscape and feeding these signals into the BAS, precise watering needs on a per zone basis can be calculated and delivered.  This approach can be quite costly considering the sensors, installation and software programming time.   Using the outdoor air temperature and solar intensity can approximate the same benefit of water management for a significantly lower installed cost.

BUILDING AUTOMATION DATA LOGGING PROVIDES BENEFITS.

Using the data logging capability of the BAS to keep track of zone watering times and actual water flows can provide a real benefit in monitoring the performance of a landscape irrigation system.  Looking over logged data graphical representations of the water quantity delivered to each zone, (multiplying the water flow per zone by the watering minutes) a maintenance person can readily spot problem areas.  Traditional watering observation and spot checking requires a lot more personnel time working nighttime or even overtime hours.

CONNECTING A READILY AVAILABLE RAIN SENSOR OR A WEATHER STATION PROVIDES BENEFITS.

Many have observed sprinkler systems watering during a rainstorm and generating a very negative impression, especially during a drought or water rationing. This can be prevented by connecting a simple contact closure rain sensor to the BAS and programming it to prevent any of the zones from watering when detecting rain.  The BAS can provide additional benefits than merely preventing negative impressions.  Timing the duration of the rain storm or receiving a rain fall quantity signal from an automatic weather station or a bucket type rain sensor, scheduled watering times can be skipped based on the amount of rain received.  If the inches of precipitation watering method is being used to meet water conservation requirements, then the rain accumulation compared to the flow being delivered would factor into the precipitation delivered per zone. An analog signal from a ground moisture sensor would accomplish the same result of automatically calculating an inches of precipitation requirement. A wind velocity signal from a weather station or wind velocity meter could be used to delay watering to prevent waste from sprayed water blowing away in high wind conditions.

INTERNET CONNECTIBILITY OF BUILDING AUTOMATION SYSTEMS PROVIDES SIGNIFICANT BENEFITS.

E-mail capability of a BAS is often taken for granted by the building owner or operator.  Alarms are typically sent to maintenance personnel web-enabled cell phones for critical HVAC process failures such as main air handler, chiller, boiler or other system problems.  Since landscape watering alarms, except for a main line break, are not as critical, instantaneous response to e-mailed alarms for broken head geysers may not be practical.  The BAS would simply shutoff the “geyser” zone, (detected by an overflow or underflow condition), bypass it in the watering cycle and send an e-mail alarm to a landscape maintenance company to come look at and repair the sprinkler head problems the next day.  Since watering usually occurs at night, e-mailed alarms can facilitate repairs to sprinkler zones that in conventional systems may take weeks to discover.   

Web pages, served up by the BAS and accessed by internet browsers, provide a convenient way to program the watering schedules for building landscape irrigation systems.  Graphical site plans can represent the landscape zones and piping and zone diagrams can be easily viewed online by the maintenance person. Since watering usually occurs at night, the maintenance person can access the irrigation control schedule and verify watering on-line, remotely from home without having to drive to the building to verify watering operation in the middle of the night.  Conventional irrigation clocks are usually cumbersome to program because they have a limited character screen display.  Often times because of the programming difficulties, the original watering schedule is never changed even if it doesn’t represent the landscape watering needs as determined by operation over time.  With web pages on-line, simple schedules can be displayed on a single page and updated easily.  During watering cycles, the total gallons delivered to a zone or a calculation of total  precipitation in inches based on the square footage of the area would be displayed on a web-page that could be accessed from the maintenance person’s home.

Web services, such as integrating weather forecasting websites can provide significant water conservation measures to the building operator who wants an automatic irrigation system that is really “state of the art.”  Weather forecasts of upcoming rain can be used to delay watering schedules.  Forecasts of extremely hot weather can be used to increase watering times.  Some agencies even publish recommended precipitation rates for irrigation on a daily basis that could also be used to adjust watering times to meet plant evaporation rates.  Because of many municipalities mandating water conservation restrictions, using the BAS with internet capability, permits the building owner to implement mandated water conservation measures without needing to purchase sophisticated irrigation time clock controllers from a traditional irrigation manufacturer.

TECHNICAL ISSUES IN BUILDING AUTOMATION IRRIGATION CONTROL

Conventional HVAC electronic control hardware is packaged for installation in indoor mechanical rooms, not underground in the irrigation valve environment.  If this type of hardware is used for the irrigation system control, control panels are usually fabricated with the required number of digital output controllers mounted together in the panel.  The wiring to the control valve boxes, located across the landscape area must be “home-run” to the control panel location.  This can result in some large wiring bundles depending on the number of zones controlled.  Since conventional irrigation clocks control all of the zones from a single enclosure, locating HVAC style digital control output modules in a single panel to connect to the existing zone valve wiring may be an effective way to use the BAS in an irrigation system control retrofit.  Connecting to flow meters or moisture sensors, on a retrofit project, with all of the valve wiring being "home-run," may require extra underground wiring installation unless there are spare conductors in the wiring bundle. 

As most building automation systems utilize a distributed network to communicate with local application specific controllers such as VAV or fan coil types, distributed network irrigation valve controllers are also available  that communicate on the LON talk protocol. Locating these valve controllers in the zone valve boxes considerably minimizes the amount of wire and the wire bundle size for larger landscape irrigation systems.  These valve controllers are totally encapsulated which allows them to operate underground or underwater which is often the case in irrigation valve boxes.  These valve controllers also have inputs so that the system flow meter, ground moisture sensors or rain sensors can be wired to the nearest valve box, to minimize wiring costs.  For a distributed network irrigation control system, only one pair of 24vac power wires along with a twisted pair communication trunk needs to be daisy chained from valve box to valve box along with the water supply lines.  The twisted pair communications trunk could be the same as the one in the building but there may be a need to isolate it with a repeater in high lightning storm areas. The 24vac transformer powering the system needs to be larger than for a typical irrigation clock because of the power requirements of the distributed valve controllers. 

An alternative to running twisted pair communications wire underground would be to use valve controller modules that communicate LON talk via powerline over the 24vac power wire pair that is run to each valve box.  A twisted pair to powerline router would be located near the 24vac transformer powering the irrigation control system.  The LON twisted pair trunk in the building would connect to the powerline router and it would communicate with the valve controllers over the 24ac power wires.  This feature would be of real benefit in retrofit applications because the existing underground wiring could be re-used to also communicate the flow meter and other sensor signals. If the BAS operates on BACnet or a proprietary protocol, then commercially available gateways or BACnet to LON talk routers would be required to use the LON talk waterproofed valve control modules.   

The robustness of the irrigation valve controller modules to be installed underground  and even operate underwater is imperative for the reliability of the BAS controlled  landscape watering system.  The author has observed valve boxes installed in low areas that are flooded with ground water continuously.  The totally encapsulated networked valve controllers continue to operate reliably even though they are under water all the time.

SPECIFYING AND SELLING BUILDING AUTOMATION LANDSCAPE IRRIGATION CONTROL

The building automation supplier has been accustomed to marketing through the architect/mechanical engineer sales channel.  To successfully sell BAS controlled landscape irrigation with all of its associated benefits, the building owner and building operations team needs to be brought into the loop.  Since the landscape design and irrigation system layout is handled directly by the project architect (or subcontracted by the architect to a landscape architect) during the building design phase, it is important to schedule presentations to the owner of the benefits of BAS controlled landscape irrigation early on in the project conception phase.  Owners are the key players who will reap the benefits of utilizing the BAS to control the irrigation during the life of the building.  If the project is located in an area of significant watering restrictions, contacting the municipality water department and making a presentation of the water conservation benefits of BAS control will certainly bring them on board.

There will be resistance at first from the landscape contractors as the building automation supplier will be viewed as a new competitor in their established marketplace.  This is where a partnering relationship with an irrigation contractor is very important.  The only part the landscape contractor will be giving up in the project is the traditional irrigation controller. He or she will still be supplying all of the irrigation piping, sprinkler heads, valves, installation and underground valve wiring.  The contractor will be able to program and monitor the watering through the BAS web-page schedule that he can remotely access via the internet at his place of business without having to drive over to the building during the installation, commissioning and warranty phases of the project.  He will be the one to receive the e-mailed "midnight geyser" alarms from the BAS to which he can respond promptly and demonstrate his customer service abilities.  He will be in a better position than his competitors to obtain long-term maintenance contracts with the building owner because of his supplying customer service with remote web interface and e-mail alarm response to quickly correct problem areas.. 

It is important to make a presentation to the owner during the project inception phase of the benefits of integrating the BAS with the landscape irrigation. The water conservation and management benefits the owner will be receiving include:

1. Early detection and prevention of "midnight geysers" from mowed off sprinkler heads.

2. Landscape watering conservation from automatic watering time adjustments based on ground moisture sensors, outdoor air temperature and sunlight evaporation effect or agency published inches of water precipitation requirements.

3. Public image enhancement from avoiding watering during rain-storms and high wind periods along with the water conserved by using these BAS features.

4. Water management of being able to meter the water going to all of the zones rather than having over-watered or under-watered areas during the life of the project.  The data logging features of the BAS allow for reviewing reports of the continuous water usage in the zones and fine-tuning the amount of water delivered through schedule adjustments.

5. If the owner is billed for municipal water usage the water conservation measures implemented by the BAS provide for an attractive financial payback.  A bonus payback would be where metered landscape water is deducted from the sewer bill.

6. A web-enabled BAS allows a building owner or operator to program, monitor and adjust his landscape irrigation along with the rest of his building via the internet using a standard internet browser.

To assist the project architect with specifications, only some minor modifications are required.  In the landscape section, typically Division 2, Section 2810 replace the section on the irrigation controller with "The timing control for the automatic irrigation valves shall be provided by the building automation system per division 15 or 17.  The building automation control modules, 24v power transformer, including any electrical enclosures to house these modules shall be provided and installed by the building automation supplier.”  Also include in Section 2810, “Provide and install a line size water flow meter at the point of connection in the pressure piping.  The meter shall be Istec Model 1700,  Hays Model MRD 1 (or equivalent) with an electrical pulse contact output of 1 gallon per pulse. Provide wiring from the flow meter to the nearest building automation system control module.”  Under the “installation section” include language that calls for the underground wiring and wiring terminations to the automatic valves to be provided by the landscape contractor as coordinated with the building automation supplier. Wiring terminations within control enclosures provided under the building automation section shall be the responsibility of the building automation supplier.  Include language that calls for the irrigation system commissioning to be a joint responsibility of the landscape contractor and the building automation supplier.

In  Division 15 or 17 depending on where the building automation system is referenced, the performance and sequence of the irrigation control needs to be specified.  Include language “that the timing control of the landscape irrigation shall be by the BAS and that the commissioning of the landcape irrigation system shall be performed jointly by the BAS supplier and the landscape irrigation contractor.”  The unique features available by using the BAS for irrigation control need to be specified.  The following features should be included as a minimum:

1. A single water flow meter installed to provide water usage for each of the zones.

2. Over flow and underflow alarms for each zone using the flow meter to prevent water wasting from “midnight geysers” or malfunctioning zones.

3. Data logging of water used per zone along with reports of “inches of precipitation” delivered for water management by the building owner or operator.

4. Water conservation program capability of watering time duration per zone continuously adjusted by automatic or manual entry of evaporation or precipitation requirements.

5. Internet capability of e-mailed alarms and internet browser watering schedule adjustments, water usage reports and manual override operation of any zone.

6. Any of the irrigation control hardware to be installed outside in underground valve boxes needs to be “encapsulated to operate underwater.”

7. Rain and/or wind sensors should be included to delay watering cycles based on the amount of precipitation received or wasting water during high wind conditions.

CONCLUSION

Building automation systems offer features that the building owner can benefit from in controlling the landscape irrigation system.  Water conservation and resource management plans can be more easily implemented for landscape irrigation systems using the features

of logging precipitation delivered, e-mailing alarms for overflows due to broken heads, and automatic watering time adjustment based on moisture sensing or evaporation calculations.  Replacing the simple timing functions of most irrigation controller clocks with the programming capability and internet web-access of the BAS provides these benefits to the building owner.

The author would welcome any comments or requests for more complete specifications.

Gaylen V. Atkinson, Atkinson Electronics, Inc.
E-mail:  gaylen@atkinsonel.com
Website for LON network irrigation valve controllers:  www.atkinsonelectronics.com 

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