Hotel Verdemar installations:  rainfall capture and solar hot water

July 15, 2009

Rainfall capture

System Description

The rainfall capture system installed at Hotel Verdemar uses mostly existing and a few new rain gutters to capture rain from the roof of the front of the hotel, which is high enough to drain through a pre-filter and into the existing storage tank under the front parking lot.

Trash racks were installed on all of the rain gutters that are used for rainfall capture.  Four-inch drain pipes collect rainfall gathered from four separate roof areas and channel the water by gravity to the inlet of the pre-filter.

The wall-mounted pre-filter incorporates an initial baffle and two stages of rough gravel filtration for exclusion of leaves and organic particulate contaminants.  It has no moving parts and operates entirely by gravity.  The pre-filter is outfitted with overflow drains to divert excess water to the drainage canal and for washing the system.  A single six-inch outlet provides gravity feed of the pre-filter product water to the buried storage tank in front of the hotel.

The storage tank inlet is controlled by a mechanical float valve.  Upon filling of the tank to its set level, the float valve seals the inlet, and water backing up in the inlet pipe eventually overflows through the overflow drains of the pre-filter.  Once it quits raining the water standing in the column empties naturally into the tank as soon as the water level drops in response to water use in the hotel and allows the float valve to open in response.

A chlorinator is installed in the pump room and is activated whenever there is flow in the rainfall collection pipe to dissolve chlorine tablets and introduce them in a separate and dedicated buried pipe into the storage tank.

A three-stage water treatment system provides particulate filtration, activated carbon adsorption, and ultraviolet disinfection of all water that is pumped from the storage tank.  This means that not only the rainfall capture water but also the water from the well all passes through the filtration system.  The purification system has three parallel legs.  During routine maintenance steps, two legs may always be kept active while the third leg is turned off for filter cleaning or replacement.  Pressure gages are present at both inlet and outlet of the treatment system.  The difference in pressure (head loss) is the primary guide of filter performance.  Filter cleaning is recommended at a 20% head loss.

A flow meter is installed in the system inlet line.  This meter provides cumulative water usage measurements and is to be used in conjunction with the pressure gages to know when filter cleaning or replacement is needed.  A daily log of these measurements is recommended; an example data log sheet is provided as an appendix to this report.

The valving in the pump room allows for municipal water to be used instead of rainfall/well water through the operation of two valves.  When municipal water is used it passes directly into the facility and does not go through the filtration system and is not metered.  All well and rainfall capture water passes through the water meter and water filtration system.

A rimmed concrete floor drain is provided beneath the suspended filtration system to allow for filter washing and exchange in the loft.  Two spigots are deployed for water quality sampling and cleaning purposes.  One spigot is plumbed to the inlet water line, and a second spigot is plumbed to the outlet water line.  Care should be taken during sampling to distinguish between these two sampling ports.

Required Maintenance

1)       Collection.  The trash racks on the rain gutters must be cleaned regularly to remove accumulated leaves and other detritus.  It is recommended that the roofs be washed down at the same time.  The first stage of the pre-filter must also regularly be flushed and cleaned.  The second stage of the filter is expected to require cleaning on a more infrequent basis, perhaps monthly stirring of the gravel and flushing with a garden hose.

2)      Chlorination.  The tablet chlorinator requires regular addition of chlorine tablets.  It is important through careful monitoring to determine the proper adjustment of the chlorine feed.  The adjustment is done with a valve, and we have left the system installed in a fully open position.  The hotel water should not be higher than 0.3 mg/L, which is the smallest residual that the colorimetric testers in use can measure.  If the concentration is higher than this, the valve should be turned down.  If no chlorine can be detected, it may be necessary to exchange the flow meter to a model with a higher dosing capacity, but these determinations must be made by initial measurements of chlorine and system performance to determine optimal settings.

3)      Particulate Filters.  The wound-string particle filter cartridges are designed for cleaning and re-use.  It is expected that cleaning of filters with a hose once every one to two weeks may be needed, but the frequency of cleaning can only be projected based on actual experience.  At the time of installation the inlet and outlet pressures were identical.  As particle filters begin to clog, the outlet pressure will begin to fall.  When the drop in pressure across the filters rises to 20% of the inlet pressure, then it is time to clean or replace the filter cartridges.  For an inlet pressure of 40 psi, the outlet trigger pressure, for instance, would be 32 psi.  For an inlet pressure of 20 psi, the key trigger for cleaning/replacement would be an outlet pressure of 16 psi.

4)      Carbon Filters.  The carbon block filters are chemical adsorption filters that remove organic compounds and chlorine.  They may be expected to last three-six months and  the gage of when to change them will be when inlet and outlet chlorine residual concentrations are identical.  These units may be eligible for retirement if there are no taste nor odor issues from tank storage and if a chlorine residual in downstream water is desired.  If that were the case the first two stages of the filter system could be converted to a prefilter / polishing filter to extend the cartridge useful life by allowing a washable pre-filter.

5)      UV Disinfection.  The ultraviolet lights require no maintenance until the bulb needs replacement, and the bulbs last for one year.  There is a blue dummy light on the control module that confirms the unit is in operation.   UV lamp change-out is somewhat complicated, and it is easy to break the protective quartz sleeve.  The first time these lamps are changed, it may be best to have one of my technicians train your staff.

Commissioning

The most important variable during system startup is the chlorine dosage.  Unlike the well pump supply line, the water flow rate from the rainfall collection system is not constant and will vary widely.  Therefore it is more difficult to meaningfully calibrate the chlorinator to provide a steady and dependable dosage.    In real terms this makes no difference to water quality because the ultraviolet disinfection units sterilize the water anyway, so the chlorine is actually a redundant disinfection method.  Chlorine residual is nearly always considered the standard beside which the safety of public water supplies are measured, however, so it is reasonable to continue to chlorinate even though it is not technically required for water purity.  The objective of chlorination in this application is to provide just enough to sustain a chlorine residual while water is in storage to ensure its continuing protection while in the tank, especially since the tank is subject to contamination from the entrance hatch. 

Testing and Monitoring

Daily cumulative water consumption and filter head loss should be tracked and logged to assist in determining a maintenance schedule.  Attached is a sheet that may be used as a guideline for a form for keeping information.   In addition to routine onsite chlorine measurements, the hotel will likely wish to take periodic samples for laboratory analysis of bacteria and chlorine residual.  Based on the rate at which filters become clogged and the rate at which the carbon block’s ability to remove chlorine is exceeded, a maintenance program can be established, and long term supplies and costs can then be determined to establish a long term operational program.

Solar Hot Water Heater

A fifty-gallon ProgressivTube solar hot water heater was installed at the easternmost point of the lowest roofline.  This location provides full insolation all day long whereas the roofs higher up all have parts of the day in which the shade from the large tree blocks the sun.  The heater is supplied by a ¾” feed line that is plumbed to the pump room itself, where a valve is located behind the second pump to turn this line off if desired.  The inlet of the heater is plumbed with a vacuum relief valve and the first string of pipe is CPVC.  The outlet of the heater is plumbed with a pressure relief valve designed to release at 100 psi.  The outlet pipeline is ¾” CPVC plumbed all the way to electrical hot water heater feed connections and the laundry room spigot.

The solar hot water heater is plumbed to the two hot water heaters that service the loft, the office area, the apartment and Room 302.  In each case CPVC valves are installed at the hot water heater that allow for the solar input to be turned off and regular cold water to be turned off as desired.  The water heaters were left plumbed from the heater with the inlet cold water closed.  A second line is plumbed to the laundry and a spigot is deployed so that connection to the washing machine can be made through conventional garden hose.

The solar hot water heater does not have any maintenance requirements.  There are no moving parts, no chemicals to add, no filters to change, and nothing to clean. 

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