Selecting Fire Pumps for ESFR Sprinkler Applications
Probably the most contentious issue in the application of fire pumps over the last few years has been the use of relief valves in ESFR sprinkler applications. ESFR systems offer many benefits to a facility owner, such as faster and more effective fire suppression, reduction of loss and damage in the event of a discharge, and cost savings. The drawback of the ESFR system is the increased complexity in building design and hazard considerations for ESFR applications. The fire pump can also add a dimension of complexity to the overall installation. The intent of this article is not to resolve the ongoing debate, but to shed some light on the alternatives available to designers when faced with selecting a fire pump for an ESFR application.
In most applications the fire pump is installed to draw directly from a municipal water source. Due to the high flows required by an ESFR system, the minimum available pressure at the maximum flow condition can be substantially lower than the pressure available at the no flow condition. It is not uncommon to have 70 psi of static and 20 psi of residual pressure as determined by a fire flow test. The problem of supply pressure variation is compounded by the fact that a pump provides more pressure at no flow (churn) than at full flow (see Figure 1).