MEMORANDUM
DATE: 18 October 2023
TO: City of Gonzalez, California
FROM: Justin Caron
RE: Pool Heater, Gas Pressure, and Options Forward
To Whom It May Concern,
Aquatic Design Group, Inc. (ADG) was contacted by the City of Gonzalez (City) to make recommendations, develop cost estimates, and provide specifications that can be used to allow the City to replace their current pool heater. ADG was contacted by City in part because ADG was the aquatic consultant on the most recent major renovation of the Gonzales Community Pool.
As a quick summary, the Gonzales Community Pool was renovated and reopened in 2016.
City staff reports the facility ran well for several years until around 18 months ago when the heater failed. Representatives from Raypak (the manufacturer) who recommended replacing igniters, filters and doing a general cleanup of the heater. GIS Plumbing were called to investigate, trouble shoot and have the heater repaired.
For background, the vast majority of pools in California are heated by natural gas as it has historically been the most readily available, efficient, and most economically viable means of doing so.
With the push for carbon neutrality and electrification some new projects are looking at providing electric resistance heaters, heat pumps, or utilizing alternative means of heating the pool water that does not include natural gas (or propane, etc.). ADG has been a part of over a dozen such projects and our recommendation at this point is that natural gas is still the most readily available, efficient, and economically viable way to heat a pool.
Our state energy codes do not allow swimming pools to be heated by electric resistance heaters unless 60% of your electricity is created on-site. Further electric resistance heaters are inefficient and individual units are not available in sizes required to heat larger bodies of water. Therefore, when utilized, a large bank of these units is required to provide sufficient amounts of electricity to heat the pool which takes up a considerable amount of space and will result in higher costs initially and on-going unless your electricity is being produced onsite.
Heat pumps are another option that is currently being utilized on various projects around the state. Heat pumps are not recommended for this project due to their own operational constraints. While efficient, heat pumps are meant to cycle and not run constantly. They also require generous clearances due to their need for a considerable amount of makeup air and space for their combustion air to flow. As a result of this several units would need to be provided with a recommended redundancy of at least 50% equating to an expensive enclosure to house the units to be built, and noise mitigation carefully analyzed.
Alternative means of pool heating such as geothermal, co-generation and fuel cell are only feasible on larger scale projects as the cost to develop them is considerable.
During the initial call with the City it was requested that a brief overview of 5 different approaches to heating the pool are discussed. These are listed below:
1. Solar systems:
a. Solar systems come in different varieties meant to achieve the same thing:
harnessing the sun’s energy and utilizing it at a project specific site. Types include:
i. Thermal Solar- Simple, inexpensive (relatively), and efficient way of heating pool water in which water is pumped from the pool system through black plastic panels where it absorbs the suns heat and is returned to the pool system at an increased temperature. A minimum of 60% of pool water surface area for the panels to be mounted is required to achieve a positive ROI (in most cases). This can be challenging on many projects. Thermal solar works well in areas that receive significant sunlight. The largest downside to the system is sightly fluctuating temperatures around the desired setpoint.
ii. Photovoltaic Solar (PV)- A energy creating panel as opposed to a water warming panel, this technology is used more traditionally on buildings and homes which require more electricity than a swimming pool typically uses. If electric resistance heaters were desired, a sizable array of PV panels would have to be utilized to produce the 60% threshold previously mentioned as required by the state. In addition to finding or creating roof space to house the solar array, a secondary enclosure would have to be created to house the series of electric resistance heaters.
iii. Photovoltaic Thermal Solar (PVT)- a hybrid system in which photovoltaic panels are directly above thermal panels. This arrangement reduces heat loss from the thermal solar panels and cools the photovoltaic panels resulting in an improved performance and efficiency of each. While a terrific technology in theory, ADG has no experience with them. ADG has been told that due to the high initial cost of this system a positive ROI is unlikely to occur over the life of the system.
iv. Evacuated Tube Photovoltaic Panels- Similar to how PV panels work, the tubes use a vacuum pressurized system to create high temperatures of either glycol or water which then run through a heat exchanger. The pool water is then piped to the heat exchanger to increase its temperature. The result is a more consistent temperature than thermal solar systems, albeit in a more costly and complicated system. Additional space is also required in such a system.
2. Rebuild Existing Heater:
a. After speaking with representatives from the City, Raypak, and GIS Plumbing as well as ADG staff it would be possible to rebuild the existing heater. However, such a rebuild will likely result in costs very similar to what it would cost to replace the existing heater and would not convey the same warranty as would be achieved with a new gas fired heater.
3. Replace In Kind:
a. A new replacement heater could be ordered and installed to provide a brand new fully warrantied solution that matches the original design intent. This solution would bring with it piece of mind in addition to providing a reliable heat source for the pool.
4. Replace with a Premium Efficiency Natural Gas Heater a. While rebuilding or replacing the existing gas heater could provide a viable solution, without fully understanding the root of the issues that caused the failure there is a chance the same issue could reoccur. More efficient natural gas fired heaters are available that would remove the heat transfer from inside the boiler and instead have the transfer occur in an external (but connected) heat exchanger. Such systems have become the basis of design across the pool industry where budget allows. These boilers can achieve up to 97% efficiency (as opposed to the current system which can achieve efficiencies around 86%). An additional benefit to this solution is that these boilers are more resistant to fluctuations in gas pressure and will be more resilient should fluctuations continue to be an issue with the available gas pressure to the site. While these boilers are more costly than the less efficient versions, they are more reliable and require less maintenance.
Prior to selecting a solution for the heater, it is highly recommended to have the gas line tested as it is likely the cause of the original issue is tied to, if not directly caused by, fluctuations in the gas line that comes to the site.
This concludes the memo. If further clarification, information, or additions are needed please let me know.
Justin Caron, MBA, CPO
Principal / Chief Executive Officer
AQUATIC DESIGN GROUP, INC.
CC. File