Estimate Fan pressure rise from ESP

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In EnergyPlus, Fan Pressure Rise is an input to most fan objects (e.g: Fan:ConstantVolume).

MEPs will usually give you External Static Pressure (ESP), and rarely Total Static Pressure (TSP).

Since what you should input in E+ is TSP (correct me if I'm wrong), are there any rules of thumb to estimate it from the ESP and basic knowledge of what filters and coils you have, or BHP? That would be useful In early design phases.

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Julien Marrec

asked 2016-02-01 10:35:34 -0500

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Correct, you need to use TSP in E+. ESP is only the static pressure for ducts and fitting. To get TSP you just add filter, coils and other devises. I think 0.5" w.c. is a reasonable early design phase assumption for coils. TABLE 6.5.3.1.1B of 90.1-2010 provides typical pressure drops for other devices.

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Lincoln

answered 2016-02-01 10:58:00 -0500, updated 2016-02-01 11:01:55 -0500

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Once you have an idea of the ventilation system component layout, you can definitely estimate the AHU's Internal Static Pressure (ISP) using rule-of-thumb values, and from there estimate the Total Static Pressure (TSP = ISP + ESP).

I've discovered that a good reference for typical pressure drops (in SI units) can be found in section 5 of AIVC Technical Note 65 - Recommendations on Specific Fan Power and Fan System Efficiency.

Table 5 on page 23 gives rule-of-thumb component pressure drops for different design considerations (poor, typical or good design). According to these numbers, AHU's internal static pressure can be anywhere between 250 Pa (1" w.c.) for a good design and 650 Pa (2.6" w.c.) for a poor design, given a typical Filter+HX+HCoil+CCoil component layout.

The External Static Pressure is usually between 400 Pa / 1.6" w.c. (for residential or smaller commercial buildings) and 750 Pa / 3" w.c. (for larger comercial buildings).

The Total Static Pressure can therefore be anywhere between 650 Pa / 2.6" w.c. and 1400 Pa / 5.6" w.c. depending on the design assumptions and building size, and this obviously has a great impact on the fan energy use. Also, the TSP will be a bit different between supply and return (usually lower on return).

This is important for EnergyPlus models but also for IES VE (when using ApacheHVAC) and eQuest models which also rely on Total Static Pressure to estimate fan system efficiency.