Dimplex ST0133 technical manual Where Vep System expansion volume

Technical manual

SOLAR

The expansion volume of the system Vep can be calculated using Equation 7.

Vep = Vsys ⋅ β		[7]
Where: Vep	[l]	system expansion volume
Vsys	[l]	total system volume
β	[-]	heat transfer medium expansion coefficient (0.00085)

The pressure relief valve pressure prv can as first approximation be used as 6 bar. How- ever, to allow for some tolerance it is recommended to calculate the pressure relief valve pressure prv in accordance with Equation 8.

prv = pop ⋅ (1 − 0.1)			[8]
Where:	prv	[bar]	relief valve pressure
	pop	[l]	opening pressure of relief valve (6 bar)

The last parameter to be calculated for use in Equation 5 is the cold fill pressure ppc of the system. The cold fill pressure ppc depends on the static height hstat of the solar thermal system and the required pressure in the highest system point pmin. The defini- tion of the static height hstat is depicted in Figure 33.

hstat

Figure 33 – Definition of static height of solar system

The pressure in the highest system point pmin should be between 1 and 1.5 bar. The cold fill pressure ppc can therefore be calculated as shown in Equation 9.

p	pc	= p	min	+ 0.1 bar ⋅ h			[9]
					m	stat
Where:				ppc		[bar]	cold fill pressure
				pmin		[bar]	pressure in highest system point
				hstat		[m]	static height of system

Equation 9 concludes the calculation of parameters required for Equation 4 to calculate the expansion vessel volume VEV. To be able to commission the expansion vessel, the membrane pre-charge pressure pmp has to be calculated as shown in Equation 10.

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ST0133 – A 02/09