Check out the plumbing
One aspect of spa design separating the simple from the spectacular is the configuration of the spa’s plumbing and hydraulics.
When it comes to plumbing, some companies tend to stick with designs that are tried and true, i.e. five simple jets, a single two-speed pump and a venturi have become commonplace.
One way builders can make their concrete spa installations more unique is to attend courses and seminars on plumbing and hydraulics. Several plumbing and equipment manufacturers offer free courses, while another option is to attend a pool and spa educational school to obtain more information. Armed with some basic hydraulic design principles, builders can break the mould and create more exotic spas with multiple jet pumps, an increased number of strategically placed jets and various levels of hydrotherapy.
Basic principles in spa hydraulics include:
- Start with jet placement and flow rates;
- Balance flow via pressure loops and manifolds;
- Number of jets multiplied by flow rate equals the total litres/gallons per minute (lpm/gpm);
- Water velocities and flow rates determine pressure loop size, e.g. if velocity doubles, head loss quadruples;
- Total head loss (friction, fittings, filters, heaters);
- Suction-side velocities should not exceed 1.4 metres per second (mps) (4.5 feet per second [fps]);
- Pressure-side velocities should not exceed 2 mps (6.5 fps);
- Suction lines are larger than pressure lines;
- Install all air lines in a Hartford Loop (above the waterline) to prevent water from backing into the blower;
- Larger lines carry more water at a lower velocity, thus lowering total head loss; and
- All pumps should be supplied by a minimum of two legal suction ports.
What to do about jets and blowers?
Multiple jet pumps result in multiple suction ports, which can become challenging to locate in a smaller spa. One option is to locate a well under one of the benches or stairs where access to suction ports is restricted. The Virginia Graeme Baker Pool and Spa Safety Act (VGBA) has led to a number of manufacturers creating large flow suction ports with a host of anti-entrapment features suitable for the confined spaces in a typical spa.
The idea of adding an air blower to the spa is also often debated. Spa jets are generally designed to operate without an external blower by venturi action. The addition of a forced air blower into the spa jet creates an increased amount of ‘action’ in the spa. Visually, the spa comes alive due to the increased air volume; however, air blowers tend to lower the spa’s water temperature, especially in the winter when cold outside air is injected into the water stream.
If not placed correctly, jets and blowers located on seats and benches can also float bathers out of the spa. Therefore, it is important to locate the air holes and jets properly. This is another advantage to building a custom-concrete spa, as jet placement can be uniquely customized to suit an individual bather.
For example, if the client has a shoulder injury, spa jets can be clustered to target that specific muscle group. Taking measurements of the client’s body, and including them in the spa’s design, can help ensure he or she has an excellent hydrotherapy experience.
Not only can jet placement be customized, but also bench heights, slopes, footrests, loungers and standup wells can be tailor-made. For the ultimate full-body massage, standup wells with more than 36 jets are entirely possible when building a custom concrete spa. Custom hot water cascades and large waterfalls can also be added for additional effects and muscle relief.
