System Overview #
innovateIT Car Wash Equipment LLC has developed a high-efficiency reverse osmosis system to provide spot free rinse service for express car wash applications.
The system features a “Flow on Demand” control algorithm to adjust pump pressure and flow to account for changes in feed water temperature, number of cars being washed and condition of the membranes.
The VFD pump allows the system to respond to the car wash demand for RO water and is sized to generate RO needed to match the demand throughout the day.
This approach allows the use of a reduced size RO storage tank which is fully integrated to the RO stainless steel stand.
In addition, the VFD pump allows the unit to produce full flow (15 GPM) down to 40F feed water temperature to ensure consistent flow for the wash even in extremely cold winter climates.
The RO usage is monitored and RO production rate is automatically adjusted to meet the demand (number of cars in tunnel) to improve energy efficiency of the system and eliminate the on/off cycling typical of existing RO systems.
In addition, the integrated system eliminates the cost of buying and installing large buffer storage tanks needed to meet the high volume tunnel demand at busy washes.
This RO system has been engineered to allow years of trouble-free operation and low life cycle cost for the operator. The system utilizes commercial (high efficiency) RO membranes which operate from 70 to 200 psi pump pressures.
All the components (chlorine filter, pumps, etc.) have been selected to improve the system reliability, minimize energy use, and reduce required maintenance.
A large touch screen Human Machine Interface (HMI) provides an intuitive screen display for the operator to use to monitor system performance.
Additional screens provide for initial set-up of the unit and the maintenance screens which document the pump operating hours and on/off cycles to help anticipate maintenance actions and reduce unplanned maintenance.
The unit includes the RO storage tank but requires a separate tank for the reject water. RO reject water is used for other wash processes which include wheel blasters, underbody spray and various rinse processes.
Principles of Operation #
The system is designed to automatically generate the required RO for the demand of the tunnel (up to 24,480 GPD with the Standard Flow system or 37,440 GPD with the High Flow system.
NOTE: Most car washes operate with varying feed water temperatures over the course of the year. This unit is designed to ensure that the unit produces adequate RO for rinsing cars across a wide range of feed water temperatures and levels of dissolved solids.
The unit uses the Grundfos VFD Pump along with a PLC controller to match the RO production to the RO usage. This approach produces high quality water with maximum operating efficiency.
The tank level sensor (pressure sensor) is used to generate the request for RO production flow rate which varies based upon the RO storage tank level.
This feature allows the system to increase flow as the tank level drops. When matched to properly sized nozzles in the tunnel, the unit is designed for up to 200 cars per hour continuously.
The variable flow approach based on tank level allows the use of a smaller RO storage tanks which integrate directly to the RO system.
The result of this feature allows the pump to operate at lower pressures for longer periods, increasing membrane life and reducing pump cycling.
This feature avoids short cycling the pump and allows unit to run efficiently even during periods of low or intermittent carwash tunnel volume.
An electrical control box is installed on the unit which includes the PLC, a mechanical disconnect from the main power supply, motor fuses, transformer to convert the 460Volt three phase power to 24 V and 110V to power the HMI and air solenoids (24Volt) and water quality TDS sensor (110Volt).
The control box also includes a motor starter for the re-pressurization pump which uses RO water from the storage tank and delivers RO flow to the tunnel.
This pump is turned on based on an RO request signal from the tunnel controller and does not integrate to the RO production pump controller.
A flow switch and an air operated solenoid valve have been added to the re-pressurization pump output to protect the pump from a dry running condition. This feature will turn off the re-pressurization pump if the flow switch fails to close.
The electrical inputs and outputs (I/O) has been selected to minimize the number of sensing devices while providing the ability to diagnose failure of the equipment.
System Operation #
The following input and output signals are used to provide the controller information to operate and troubleshoot the system. These sensors are shown on the system schematic.
Pump Inlet Pressure Switch PRS1
0-5 psi adjustable pressure switch which is used to detect an issue with the water supply. If this switch fails to closed after start-up it will turn off the RO pump and register a system fault. A PRS1 fault will shut down the RO Production Pump and log a faut in the data log.
RO Pump Pressure Sensor PRS2
This pressure sensor is used to protect the system from operating over the setpoint pressure.
The system should be able to produce 10 GPM (Standard Flow) or 15 GPM (High Flow) of RO below 200 psi at water temperature above 40F.
If pump pressure exceeds the programmed maximum pressure setting (see settings for the HMI) the pump will be automatically reduce RO pump speed to maintain the maximum pressure setpoint even if the membranes cannot produce the requested flow.
This pressure set point is adjustable to allow use of membranes which might be lower pressure or cold water membranes.
This situation may occur as the membranes reach end of life or if feed water drops below 40F.
RO Product Flow Sensor – ROFLO
This sensor provides the feedback signal to the pump controller to adjust RO Pump speed and pressure to achieve desired flow rate. The programmed flow rate is adjustable on the PLC settings screen. The unit can be programmed to three flow levels based on three tank levels.
This sensor provides a 4-20 ma signal to the controller and the calibration is set in the controller software. This allows the operator to adjust the requested flow based on the tank level. As the tank level decreases, the flow should be set to increase. This approach allows the unit to generate RO at the lowest energy cost to meet the flow required by the tunnel.
The innovateIT unit has a curve programmed in to optimize the unit operation. Most operators should utilize the factory default; however, the RO production turn-on level can be adjusted if desired.
The tank is divided into three sectors which allow flexibility in set-up. The objective is to allow the unit to adjust flow based on tank level with lower flow rates as the tank is nearing 100% full and higher flow rates as the tank approaches empty.
The ‘RO Production Turn On’ level is adjustable and will normally be set in the 60% range. Based on these settings, the unit will ramp from 0 GPM to 8 GPM when the tank reaches 60% full condition.
If tank level drops below 50%, flows should increase to 9 GPM. If the number of cars coming through the tunnel is low, the tank will continue to fill until it reaches 90% at which point the flow will drop to 6 GPM.
These settings and requested flow rates can be adjusted by the operator; however, the following values should provide the best performance for the system and achieve the highest energy efficiency to provide RO water to the tunnel.
* RO Turn On Level – 60%
The VFD Settings are used to define the rate the VFD pump command changes. These are set based on system testing and should not be adjusted by the operator. To verify the system is working correctly, turn ON tunnel command and allow the tank level to drop
Verify the RO pump turns on at 60% tank level (or programmed set point per settings) with a flow of 7 GPM. Pump speed and pressure should increase as the level drops below 40% to achieve 10 GPM RO flow into the tank.
Once the re-pressurization pump is commanded off, the unit will keep running continuously until the level reaches 100%. The system will then initiate a RO MEMBRANE FLUSH CYCLE before shutting down.
During the flush cycle, the RO pump circulates a few gallons of RO water to the feed side of the membranes. This RO water pulls deposits from the surface of the membranes. The flush water remains in the membranes until the tank level drops to the turn-on level.
Using this method, the feed (concentrate side) of the membranes will always be cleaning the membranes between the RO production cycles.
Tank Level Sensor
The tank sensor is low pressure sensor that measures the static water head pressure based on the depth of water in the tank.
The 0-5 psi sensor is scaled to a 4-20 ma signal. This signal is used to requested flow rate based on the tank level. This signal is an input to the PLC which is used to modify the flow request based on the tank level.
Recirculation Flow Switch
The recirculation flow switch verifies that the recirculation loop flow (the combined flow of the recirculation flow and reject flow) is operating at more than 12 GPM of flow during operation.
This switch protects the membranes from fouling, verifying that Solenoid C is open and the recirculation flow orifice is not blocked during RO production. If the reject flow orifice or the recirculation orifice becomes blocked it would increase RO recovery beyond the membrane limit and damage the membranes. The switch will not close if the RO pump pressure is less than 70 psi.
The RO pump speed should be set so that the minimum RO pump pressure is set to 70 psi. The municipal water regulator for the feed water needs to be set to 40 psi. These two settings ensure that there is adequate recirculation flow to protect the membranes when operating at low pressure (i.e. when using high temperature > 70F feed water).
The switch should close as RO pressure at the pump reaches 70 psi.
Re-Pressurization Pump Flow Switch
This switch verifies that when the RO Request for water is sent from the tunnel controller, Solenoid D has opened, the delivery pump has turned ON and RO water is flowing to the tunnel.
If this switch fails to close it will turn-off the re-pressurization pump to protect it from running in a dead headed condition. Verify the switch operation by removing the switch and manually activating the switch to ensure it closes as flow increases.
System Functions #
The following outlines the operating steps in AUTO MODE. Each of these functions is designed to ensure a reliable and consistent supply of RO water for the spot free rinse portion of the wash.
- The unit will always start-up in the OFF mode.
- In this mode, power is supplied to the RO system and the 24vac signals are energized. However, the pumps and solenoid valves are all commanded off.
- The HMI will show a red dot in the mode button on the main screen.
- The unit should be commanded to AUTO MODE by the operator using touch screen using the mode select from the main screen.
- The operator will then touch Production Auto Mode and re-press Auto Mode
- This Auto mode will produce RO water until tank is full. Once full, the tank float closes and initiates a flush of the membranes.
- Once the flush is completed, the unit will turn off RO pump and wait until RO level drops to the “TURN-ON Level (based on the RO tank level sensor). At this point the RO will produce 7 GPM of flow to begin re-filling the tank.
- If usage in the tunnel exceeds 7 GPM and the tank level continues to drop (based on usage to rinse cars) then the RO production flow rate will increase to 10 GPM.
- The RO pump will continue to operate until the tank reaches the 100% FULL condition.
- Once full the unit will perform a flush and turn off to wait for the tank level to drop.
Note: In the event of either low RO flow from the system (due to failed membranes or pump problem) or if the demand from the tunnel exceeds the flow from the RO system, there is a municipal water line that uses a Jobe float to fill the RO tank if the water level drops to approximately 4 inches depth of water in the tank.
This is to protect the re-pressurization pump and ensure rinse water is delivered to the tunnel.
Municipal water has much higher TDS than the RO water and will combine with the RO water produced to create a mixture which will have TDS between the RO production and municipal water levels.
It is likely that this water will form spots if not removed from the car during drying, so it is important to verify that the usage is less than the production flow during a high volume day.
If the RO unit is off-line due to a fault, this back-up system using municipal water allows the operator to continue to wash cars.
The RO system controller has a relay which closes when the unit has a fault. This feature can be wired to the system controller to notify the wash operator of a fault from the RO unit.
TUNNEL SIGNAL COMMAND FOR RO WATER DELIVERY TO TUNNEL
- This signal is controlled directly by the tunnel system controller using a 24 Volt DC relay signal to the RO System Controller and is used to turn on the Re-Pressurization Pump.
- This signal switches on and off for each car in the tunnel based on the belt speed. The re-pressurization pump is limited to 180 cycles per hour (maximum cycle rate).
- If the belt speed exceeds the 180 per hour rate, the operator should use a look ahead feature on the car wash system controller (which leaves re-pressurization pump on) to avoid exceeding the cycle rating established by the pump manufacturer and creating a potential thermal overload of motor or motor starter.
RO STORAGE TANK
- The stainless steel RO storage tank is integrated onto the stainless steel stand. Municipal water flows to a solenoid inside the tank to automatically supply municipal water to the tank if there is a failure in the system.
- This municipal water passes through the carbon block assembly to eliminate the chlorine from the water and protect the membranes from free chlorine damage when using the RO tanked water for flushing.
- The municipal water back-up prevents dry-running of the re-pressurization pump by adding municipal water to RO tank.
Note: The solenoid supplies water if the RO pump or membranes have reduced the RO flow.
The 24V DC signal may be present in system controller even when the controller power has been manually disconnected from the 3 phase power source.
You must turn off the 24 V electrical signal (RO Request) from the RO system controller prior to performing maintenance or repair to the system controller. Failure to de-energize this circuit could lead to equipment damage or personal injury.
System Performance #
RO systems are designed to provide spot free rinse water to the car wash tunnel and are rated by volume of RO water produced per day. Membranes are very sensitive to feed water temperature and will typically lose approximately 2% of flow for every 1F drop in feed water temperature.
The innovateIT RO System is conservatively rated for constant performance from 40F to 80F feed water temperatures. The system utilizes oversized membranes operating at conservative flux ratings combined with daily RO flush cycles to achieve high quality water and long membrane life.
This provides 10 GPM (Standard Flow)/15 GPM (High Flow). The maximum commanded flow at low tank levels is 12 GPM (Standard Flow)/18 GPM (High Flow). These flow rates result in long membrane life and consistent RO available for the wash process.
This system has been optimized to support a car wash that requires a maximum of 18 GPM (25,300 GPD) or 26 GPM (37,950) RO Production rate. The system uses the RO FLOW SENSOR to increase RO pump flow and pressure to achieve the requested flow rate. The pressure required to generate full flow will range from 70 psi (@ 80°F) to 200 psi (@ 40°F).
The Grundfos VFD pump has been oversized to allow this wide range of temperature capability while using Dupont (formerly Dow Filmtec) membranes which ensure high quality (low TDS RO water). The VFD pump also allows only pumping at the correct pressure and flow to generate the needed RO flow to support the tunnel demand.
Although the unit has a 7.5 HP pump, the majority of the time this system will be running much lower power. The electrical energy used to generate the RO increases as the RO membrane flow increases.
The result of generating RO at the rate required to satisfy the tunnel demand results in reduced energy consumption per gallon of RO produced. The membrane’s performance varies as the feed water temperature changes. In general, at a fixed pressure across the membrane the flow will reduce 2% for every 1°F reduction in feed water temperature from the 77°F rated temperature (77°F is the industry standard rating temperature).
This means the RO pump pressure must increase to maintain flow as feed water temperature drops.
The table below illustrates the impact of feed water temperature on the membrane flow and pressure. The innovateIT RO system uses pressure and flow sensors to control the recirculation flow and pressure needed to automatically generate 10 GPM of RO without requiring manual adjustments.
closed after start-up it will turn off the RO pump and register a system fault. A PRS1 fault will shut down the RO Production Pump and log a faut in the data log.
fig. 2.4 – 1 – RO System Performance
RO Pump Pressure Sensor PRS2
This pressure sensor is used to protect the system from operating over the set point pressure. The system should be able to produce 10 GPM of RO below 200 psi at water temperature above 40F.
If pump pressure exceeds the programmed maximum pressure setting (see settings for the HMI) the pump will be automatically reduce RO pump speed to maintain the maximum pressure set point even if the membranes