As with everything in life, there is right way and a wrong way to design a geothermal valve vault. Here, Joe Pejsa shares his recommendations for the right way based on years of experience and hundreds of installations.
1 Use a Two-Manway System
There are two primary advantages of using two manways in a vault design.
- Per OSHA standards, proper ventilation must be provided to safely work in a confined space (i.e. a buried valve vault). Ventilation in a vault is provided with a positive pressurization fan so that fumes from the surface can’t be introduced to the workspace (such as vehicle exhaust). The fan can’t be permanently installed inside of the vault, so it can be stored in the second manway for easy removal and use.
- The working space in a vault is limited and it is easy to get crowded. Two-manway systems improve access to flush and fill ports without blocking your exit. If something goes wrong and you need to get out, two access points make a lot of sense.
2 Always Include a Bypass
A bypass is a necessity for every geothermal manifold, including vaults. With vaults, a bypass should be placed in the vault(s) as well as in the building. This allows for segregation of interior and exterior piping, which decreases pumping requirements on your flush cart. Plus you be able to prevent the dirt and chemicals from one side of the piping system from getting into the other while you are prepping the system for operation.
3 Manifolds Need Isolation Valves and PT Ports
Every geothermal manifold should also include means to isolate individual circuits (via butterfly valves) and take performance measurements (via P/T ports). In general, some level of isolation will be necessary for any loopfield with multiple parallel circuits. At some point, there may be a need to:
- Isolate either the main supply-return lines to the building or the individual loopfield circuits during pressure testing or flushing/purging
- Make slight flow adjustments to individual circuits in order to balance flow through the entire loopfield
- Isolate a problem such (as a leak) in order allow for repair while preventing a total shutdown of the system
Butterfly valves are the most common and economical choice for isolation valves in a geothermal manifold.
In addition to isolation valves, the manifold design should include P/T ports to allow for performance measurements. In terms of placement in the manifold, P/T ports should be placed:
- On each circuit, on the loopfield side of the isolation valve (as opposed to the manifold side of the isolation valve)
- In one or two locations on the mains, such as the interior and exterior vault bypass.
With proper usage of isolation valves and P/T ports in a geothermal manifold, loopfield flushing, purging pressure testing, commissioning, performance checking, maintenance and repair will be simple and straightforward.
4 Make it Waterproof
A geothermal vault will not be entered on a daily, monthly or yearly basis which makes 100% resistance to water intrusion critical. After all, a slow drip over a year can add up to a significant volume. A leak free vault housing would lower maintenance costs by:
- Decreasing corrosion of valves and mechanical components
- Eliminating need to make provisions for electricity and sump pumps inside the vault
- Saving maintenance personnel time wasted pumping water from the vault prior to entering it to perform a system check or periodic maintenance
Environmentally speaking, a leak free vault would prevent the antifreeze solution from contaminating the surrounding area in the event that a leak occurs in the manifold. This can save you from costly environmental assessment and clean-up in the event of a mechanical component failure.
5 Use HDPE for the Housing
A loopfield should be viewed as an investment in permanent infrastructure on the site. HDPE is used to construct the loopfield in part because it has a service life expectancy of more than 100 years. Even if a building is torn down or somehow destroyed in 75 years, the loopfield will still be there ready for use. The same logic should apply to a geothermal vault. If the vault housing is made of the same material as the loopfield, the vault and loopfield will have the same life expectancy.
Stick to these principles with your next geothermal valve vault for maximum utility and minimal issues. Now that you know what to include, read 5 Features of Bad Vault Design for things to avoid with your next vault design.