International Watershape Institute

All position papers

Position Papers

3. Fluid Mechanics Performance for Watershapes

Last updated:  

01/01/2020
Open/Download PDF

Introduction

Watershape University is the leading education system for the pool, spa, aquatics, and outdoor living industry. The experience and expertise of our instructors has resulted in this Position Statement intended to guide our students and Corporate Engagement team toward better projects.

This Position Statement was assembled with input from leading professionals in the pool and spa industry including individuals that are not members of Watershape University. The contributors share a common goal of improving safety, reducing energy consumption, raising the current standards, and building better quality projects. The positions are not biased toward specific manufacturers or products.

This document is not a consensus standard or building code. It has not gone through the consensus procedures of any recognized standards writing authority. Watershape University has little interest in pursuing the consensus process that would only dilute these positions with inferior concepts based on specific products, technology, maintaining backwards-compatibility, or other conflicts of interest. Use of this document is completely voluntary.

This document is made available in the public domain. Watershape University encourages the free distribution, use, and reference of this document in whole or in part. Individuals or firms involved with the design, engineering, construction, maintenance, and operation of pools, spas, and water features may use this Position Statement to guide their work; however, in no way does this relieve them from compliance with all laws, codes, standards, regulations, ordinances, or other requirements. Individuals and companies involved with the development of standards and codes are encouraged to consider these Position Statements and the associated Commentary. Authorities having jurisdiction may reference this document directly as a building code in whole or in part.

Watershape University reserves the right to add to, delete from, or otherwise modify this document at any time without notice. The positions stated herein represent sound thinking on the date of publication given the current state of technology, experience, and information. Watershape University recognizes that “one size does not fit all” and that there are exceptions to every rule.

In publishing this document, Watershape University disclaims all liability and is not responsible for any loss, damages, or injuries that may result from reliance upon the statements contained herein.

Format

There are two columns. The first column clearly and concisely states our position. The second column provides commentary and justification for the corresponding position statement.

Format

Each position statement is divided by lines.  The beginning of the section clearly and concisely states our position. After the line break, we provide commentary and justification for the corresponding position statement.

Position Statement

Commentary

3.1 Automatic Fill Device
3.1.1 An automatic fill device shall be installed.

Low water conditions may create safety hazards including increased risk of suction entrapment on skimmer equalizers, shallow diving envelopes, and potential damage to equipment.

IAPMO/ANSI USPSHTC 1 – 2009 section 306.2 states that the connection to the fill device “shall be protected by an air gap or a reduced pressure principle backflow preventer” (RPBP).

3.2 Overflow Line
3.2.1 An overflow line should be installed.

Without an overflow line, if the water level reaches the rim of the pool or surge basin the water may flood decks, damage landscaping, damage nearby structures, etc. It is preferred that the overflow be controlled.

3.2.2 Overflow lines should discharge to the storm drain for outdoor pools and the sanitary sewer via an air gap for indoor pools; however, local codes may have specific requirements and the authorities having jurisdiction shall be consulted.

The preference is that chlorinated water is not discharged to the storm drain but it is generally acceptable to discharge to the sanitary sewer. However, if a pool receives precipitation, the resulting consolidated flow rate (rain across the entire pool surface area and decks that slope to it) could easily peak at rates that exceed a sanitary sewer’s capacity – resulting in a sanitary sewer overflow (SSO) where untreated sewage is discharged into the environment. This is not expected for indoor pools where an overflow connection to the sanitary sewer via an air gap is appropriate in most situations.

IAPMO/ANSI USPSHTC 1 – 2009 section 313 states that when wastewater is discharged to the sanitary sewer, there shall be an air gap connection to a minimum 3” sewer line. This applies to equipment maintenance drains, filter backwash lines, etc. It is up to the local authorities having jurisdiction as to whether precipitation overflowing a pool is considered wastewater.

3.3 Flexible PVC Hose/Tubing
3.3.1 Flexible PVC hose or tubing shall not be used.

IAPMO/ANSI USPSHTC 1 – 2009 section 311.1 states: “Listed plastic circulating piping and fittings for non-threaded applications between all mechanical equipment and pools, spas, or hot tubs shall not be less than Schedule 40.” Hose and tubing are not included in this requirement.

IAPMO/ANSI USPSHTC 1 – 2009 section 311.2 states: “Listed plastic threaded circulating pipe between all mechanical equipment and pools, spas, and hot tubs shall not be less than Schedule 80. Threading of plastic pipe in the field is prohibited. Threads shall be molded.” Hose and tubing are not included in this requirement.

IAPMO/ANSI USPSHTC 1 – 2009 section 311.3 states: “Plastic piping shall be permitted to be cold bent for sizes two (2) inches (50 mm) or less with a radius of not less than five (5) feet (1524 mm) without the application of heat. Bends of small radii and exceeding two (2) inches (51 mm) shall be manufactured with the use of thermostatically controlled equipment and shall be listed.” Hose and tubing are not included in this requirement and we believe that the heat bending requirement reinforces the fact that rigid PVC pipe should be used since hose and tubing does not require special practices to bend it.

Flexible PVC hose is easily kinked if the minimum bend radius is exceeded. Even if not kinked, any deflection of the circular cross section decreases the area and increases the velocity in that section – excessive velocities increase headloss and wear the pipe prematurely.

Although most flexible PVC hose has a somewhat smooth interior surface, they typically have bumps from the corrugated structure and this increases headloss.

The wall thickness is typically more than equivalent rigid PVC pipe so headloss is also increased over comparable pipe sizes.

Vacuum pressures have collapsed flexible PVC hose and it is also easily crushed by tree roots.

Water-hammer has been demonstrated to cause flexible PVC failures at solvent-welded joints.

Termites have damaged flexible PVC hose.

3.4 Surge Basins
3.4.1 Surge Basins for vanishing edge and slot-edge systems shall be filtered.

Water-in-transit systems serve as skimming systems even when dedicated skimmers are included on a separate filtration system. Without a filter on the surge basin, collected debris is returned to the main vessel, creating unsanitary and cloudy water conditions, and maintenance problems.

3.5 Filters
3.5.1 Cartridge filters shall be limited to 0.375 gpm per square foot of filter surface area.

This has been a commercial limit for many jurisdictions. Anything higher risks damage to the cartridges and results in excessive headloss.

3.5.2 Sand filters shall be limited to 15 gpm per square foot of horizontal surface area. We recommend that sand filters be limited to 12 gpm per square foot of horizontal surface area. Sand filters should be backwashed at 15 to 18 gpm per square foot of horizontal surface area in order to suspend the media and release trapped debris.

It is common to see sand filters in the pool industry rated for 20 gpm per square foot. This unit flow rate will result in channeling of the media – especially with the typical short-profile filters common in the industry.

3.6 Skimmers
3.6.1 Skimmers shall not be operated above the manufacturer’s recommended flow rate. For common 8” wide floating weir skimmers, this is usually about 75 gpm.

High flow rates in the skimmer can result in vortexing and air entrainment that is problematic for the pump.

3.6.2 Skimmer equalizers shall not be required. When installed, they shall be installed in split pairs separated by 3-feet clear.

Skimmer equalizers are used to prevent pump damage when the skimmer runs dry due to low water level or blockage by debris. The low water level issue is easily solved with automatic fill devices that are standard on all new pools.

Skimmer blockage by leaves or other debris is a valid concern in some environments but not all. Many pools (e.g., indoor or those without problematic vegetation) may never have blocked skimmers so there is no justification for the equalizers.

Even if a pump ran dry, the resulting damage and expense would be insignificant compared to the risk of suction entrapment on the equalizers.

When equalizers are installed they should be installed in split pairs separated by 3-feet clear or on different planes in conformance with all the standards pertaining to regular split suction outlet pairs. This is because a float valve in the skimmer will effectively turn the equalizer into a suction outlet.

2. Energy & Resource Efficiency for Watershapes

View all Position Papers

4. Structural Requirements for Watershapes