a.Temperature and Flow Requirements – An existing parallel piping system may be used, provided the return water is not below 80°F and the return water temperature is not more than 80°F less than the boiler outlet temperature. A flow analysis should be performed to determine the flow through the boiler when the minimum
(and smallest) and maximum number of zones are activated.
Sufficient flow through the boiler must be maintained. The recommended maximum temperature difference between the boiler supply and return water is 40°F. However, a maximum delta T of 80°F across the boiler is allowable.
A minimum boiler supply water temperature of 130°F must be maintained to avoid sustained condensing within the combustion chamber.
b.Primary/Secondary Piping - If the conditions above cannot be met, then parallel piping systems must be converted to an arrangement that will provide the proper water flow through the boiler at the proper temperatures. Primary/ Secondary piping is a common method for isolating the boiler from the system. The concept must be for the boiler loop to inject heat into a primary loop, provided the return water into the boiler is at least 80°F. A
Figure 51: Parallel Piping Conversion
Multiple boilers are installed the same as single boiler installations. Each boiler loop will contain its own boiler circulator (see Figure 49b).
The boiler circulator selection will maintain a constant and minimum flow through the boiler during every heat demand. The circulator must be properly selected, based on the design temperature between the boiler supply and boiler return. A boiler circulator must be used with a primary/secondary piping arrangement.
Figure 52: Typical Burnham Boiler -
Primary - Secondary Loop System
c.Alternate Piping Arrangements - Piping arrangements other than Parallel and Primary/ Secondary, such as System Bypass, are acceptable as long as they ensure that the flow and temperature requirements of the boiler are met.
d.Glycol Antifreeze Solutions - Many systems today use ethylene or propylene glycol antifreeze solutions as a measure for freeze protection, as well as a pump lubricator and corrosion inhibitor. The properties of the glycol mixture have an impact on valve and pump sizing. All glycol solutions have a lower specific heat than water.
This means that the glycol solution cannot transfer heat as well as pure water, resulting in the need for higher flow rates. In addition, the viscosity of the glycol solution is usually higher than water, requiring a higher pump head for the same given flow. Consult factory for specific applications, pump selection and flow rate.
e.If this boiler is used in connection with refriger- ation systems, the boiler must be installed so that the chilled medium is piped in parallel with the heating boiler using appropriate valves to prevent the chilled medium from entering the boiler. See Figure 53.
