Keep your cool with Roof Mister
QUESTIONS AND ANSWERS
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Q) What are the physical properties that support roof cooling? A) Roof cooling is based on the fact that water, as it evaporates, absorbs large quantities of heat. For example, one gallon of water at 100°F will, in evaporating, absorb approximately 8500 Btu's. In other words, the evaporation of less than 1-1/2 gallons of water over an hour’s time will absorb 12,750 plus BTUs more heat than a one ton mechanical air conditioner.
Q) Does the water temperature have an effect on the cooling efficiency of the system? A) Yes, but it is very slight. For example, for water at 120°F, the amount of heat absorbed at the change of phase is approximately 2% less than it would be at 80°F. [For other temperatures, check the steam tables (Thermodynamic Properties of Steam, Keenan and Keyes)]
Q) Is the water recirculated? Is my roof flooded? A) There is no water to re-circulate. The controls for the system insure that only the amount of water that can be evaporated for the existing conditions on the roof at that particular time is misted. Therefore, all of the water misted on the roof is evaporated. The reason for Roof Mister’s emphasis on very low volume spray heads and a sophisticated (but not complicated) control system is to monitor the water requirements and flow to the extent that even on sloped metal roofs there is no run off. The roof's temperature is the primary, although not necessarily the only, determining factor in calculating the immediate values of the misting cycles needed by the roof. Additional information from other analog type sensors can be incorporated (wind speed and direction, light intensity, etc.). The roof is misted for only a few seconds each cycle, after which the mist evaporates in a few minutes. So the roof is cooled but dry most of the time. (Under normal operating conditions, the misting occurs approximately 6 to 10% of the time (3.6 to 6 minutes an hour)). On average a Roof Mister system will use less than one pint per square foot per day, resulting in a typical operating cost in water of $2.50 to $3.00 per 1,000 square feet per month.
Q) Do I have to use city water? A) No. We have systems that operate using river water, pond water, treated waste water and well water. When using city water, typically the sewage charge can be waived, since the water used for the system is evaporated. Normally, the sewage charge constitutes about 1/2 the total water bill.
Q) Does the system require a pump? A) For optimal performance on large systems, 75 - 90 psi is required. The increased pressure allows the system more control and flexibility. Roof Mister can specify and/or provide the booster pump, pump controls, and piping design and/or assembly.
Q) My water is of very poor quality, will it clog the spray heads? A) We have over 2-1/2 million spray heads in operation, with systems operating in 19 states and several foreign countries. In addition, we have a lifetime guarantee on each spray head against clogging. There are several reasons for this: 1. Each spray heads is filtered. 2. The spray heads itself is constructed from ABS and Celecon. The advantage of these plastics is that they are very slick (high lubricity) and simply do not collect precipitates as do metal spray heads or nozzles. 3. A filter can be placed in the system, if required. In the long run, however, the spray heads lifetime warranty protects the customer from clogging problems, and the fact that we can offer this guarantee, is indicative of our experience that clogging is not a problem.
Q) What will the installation of a system do to my roof warranty? How will it effect the life of my roof? A) The system has been installed on many types of roofs; single ply roofing (EPDM, PVC, etc.), built up, metal, asbestos and modified bitumen roofs. Many systems have been installed strictly to extend the life of the roof.
Q) How is the system anchored to the roof? A) The hydraulic and the electric system (conduit) are mounted on Roof Mister’s supports which are in turn attached with an adhesive that is compatible to the roofing membrane. The roofing membrane material is not penetrated.
Q) I am going to have to replace this roof in a few years. Can I remove and replace the system? A) We have had several customers replace their roofs after the installation and because of the design of the system it has presented no problems. A system of 100,000 sq. ft. can be easily disassembled into segments and removed from the roof by two men with pipe cutters within 1 - 2 days. Reassembling would require approximately 2 - 4 days.
Q) Does the system require a pump? A) For optimal performance on large systems, 75 - 90 psi is required. Roof Mister can specify and/or provide the booster pump, pump controls, and piping design and/or assembly. The increased pressure allows the system more control and flexibility.
Q) I have mechanical equipment on the roof. Will this be sprayed? A) Our designer and technicians check with the maintenance staff or owners of the facility to insure that any equipment on the roof that is to be avoided can be taken into consideration in the design. Directional spray nozzles (360o, 270o 180o and 90o) can also be employed to avoid spraying equipment.
Q) My maintenance staff is on the roof often. Will they get wet? A) The spray emitted does not normally get above the knee, and it is, of course, very light. In addition, a particular field can easily be deactivated by means of a control handle atop the solenoid valve. Finally, it has been our experience that the maintenance staff finds the cooled roof a much easier environment in which to work and normally they will avoid disabling the system unless it is absolutely essential.
Q) How is the system constructed? A) The system is a network of Roof Mister UVRPVC tubing and spray heads placed atop the roof on 10' to 20' centers. The network is subdivided into "fields", which are activated by the Roof Mister controller, normally one field at a time. 1. Each field is controlled by 24 VAC pressure differential solenoid valves. 2. The main or supply line constitutes a manifold supplying water to the fields. 3. The roof sensor(s) is (are) placed under a thin coating of mastic on the roof surface. 4. The control enclosure can be placed virtually anywhere the client wishes.
Q) Why do you put your wiring on the roof in conduit since it is 24 volt and is not required by code? A) We put all of our wiring in conduit in order to protect it from people's feet, the elements, and for aesthetic reasons.
Q) Is Roof Mister’s controller just a timer? A) No, the amount of solar radiation impinging on the roof varies, hour by hour, throughout the day and varies day by day. Likewise, the amount of water required varies throughout the day with the morning and evening requiring less than what is needed during midday. A set time "on" and a set time "off" obviously does not allow for this, resulting in a system that will be set correctly for only two times throughout the entire day. In addition, the weather conditions are constantly changing and so does the amount of water required to maintain the roof surface temperature at its lowest point. Therefore, the problem with controlling a system in this non-responsive fashion is that the amount of water issued to the roof is either too much or too little for the majority of the time. When too much water is issued, you have runoff and water is wasted. When too little water is issued, the roof’s temperature rises and the heat entering the building through the roof increases. By contrast, the Roof Mister’s control system monitors (every 1/10 sec.) the temperature of the roof and/or other weather conditions. The controller constantly monitors and adjusts the on-time of the misting spray and the frequency of the spraying cycles, in order to minimize both the roof temperature and the water usage. It is the weather/temperature conditions at the roof’s surface at any time, minute by minute, hour by hour, day or night, that determines if, when, and how the Roof Mister system will operate.
Q) What if my control system goes down? A) The control system is built of standard, interchangeable, commercially available, components that are modular in design and require nothing more than a screwdriver to replace. Modules can be replaced, depending upon available stock, within 48 hours. The CIM (Customer Interface Module) is provided with every Roof Mister controller. This module allows a person to adjust particular options within the PLC without concerns of harming the "basic" program (a Factory Reset button is also present). The CIM also allows the customer to monitor the system's inputs and outputs, as well as informing the customer with alarms. This module is normally physically attached to the controller(s), although a portable CIM device is available. Another option is to incorporate a modem with the system. With this option, we recommend that most customers supply a standard (analog) phone line to the controller. This allows, a Roof Mister technician from any location (at the office or in the field), the ability to monitor, troubleshoot or adjust the program at the facility (Domestic as well as Overseas). Also, every customer’s individual program is kept on file. If a modem is not installed on the controller and the program needs adjusting, the program can be emailed to the customer and downloaded into the CPU with the supplied communication cable. If the CPU needs replacing along with the program, the program can be downloaded into another CPU and next-day aired to the customer.
Q) What if I wish to monitor or control the PLC? A) Many customers are uneasy with the idea that they can not control or monitor the system or the controller may be in a location that is not easily accessible to a analog phone line. For those who wish to be able to adjust the amount or the frequency of the misting, Roof Mister offers two types of interfaces to the PLC. 1. The CIM (Customer Interface Module), which is standard equipment with all Roof Mister controllers, allows a person to adjust particular options within the PLC without concerns of harming the "basic" program (a Factory Reset button is also present). The CIM also allows the customer to monitor the system's inputs and outputs, as well as informing the customer with alarms. This module is normally physically attached to the controller(s), although a portable CIM device is available. 2. The HMI (Human Machine Interface) is an event driven monitoring system software that is loaded onto a customer computer/s and gives the customer many various visual displays of the system. For example (but not limited to): a. Display Panel/s: Real-time displays of the system and fields operating (graphic and analog/digital) , b. Control Panel/s: Allows the customer to change certain aspects of the program without concern of damage to the program, such as misting times, frequencies, activation / deactivation of the system and or sections of the system, c. Information Panel/s: Displays the information from all inputs and outputs of the system, d. Logging Panels: Shows multiple real-time trend graphs over various hours / days. Also data-log files may be generated automatically showing input information.
Q) Which should I consider for my system? A) This depends upon a number of things. The CIM is standard and most customers prefer this type of monitoring and control for systems under 250,000 square feet that have minimum number of input signals (sensors). The HMI option is more expensive due to the cost of the software and added programming for both the PLC controller and the HMI software (customized graphic screens for the customer’s computer). It is more ideally set for very large systems or systems with multiple or remote controllers and requires that the customer have means to communicate with the controller, such as a modem, and a computer with the requirements needed to load the HMI software. Some customers use both types in tandem. For more information about which option is best for your facility, please call us at 256-757-5366.
Q) How much maintenance does the system require? A) The system requires very little maintenance. Two items must be addressed during the year: 1. Winter: drain/blow down and 2. Spring: startup The system is constructed of Roof Mister’s UVRPVC tubing (specifically manufactured to our rigid specifications) with high quality solenoid valves, and, of course, spray heads and the control system. The only moving parts of the system, are the 24 VAC solenoid valves and in some systems the "rotor spray" nozzles. The Roof Mister controller is industrial grade and will retain the program memory with no power. Because of the intelligent program, the controller itself needs no adjustment by plant personnel.
Q) The system may freeze in the winter, how can damage be prevented? A) In order to avoid freezing and subsequent damage, the system is "blown down" for the winter. Roof Mister provides manual drain valves and a pneumatic fitting to which a compressed air line can be attached. In the spring, the system has to be restarted and, of course, checked for proper operation. Opening the water valves and applying the power to the controller is all that is needed.
Q) What about a "freeze protection" program? All Roof Mister controller programs include a subroutine that provides emergency freeze protection from sudden, unanticipated drops in roof temperatures. The controller activates the system, intermittently, to prevent damage during these conditions. Complete automatic winterization of the system is also available. This option monitors the roof temperature and after specific conditions are met, the controller runs subroutines to evacuate the system of water.
Q) How long can I expect a system to operate? A) From a cost consideration, the most critical component in the system is the exposure of the tubing to the sun’s ultra violet radiation. The Roof Mister UVR-PVC tubing, made especially for Roof Mister, is a co-extruded type, with the outer shell of the tubing containing over 10 times the normal amount of titanium dioxide found in typical PVC tubing. The manufacturer assures us that our tubing, exposed to sunlight, will have a life expectancy of 25 plus years. |
