Step 1 : recalculation of the tapflows

Introduction

Some diversity standards like the DIN 1988-300 (Based on DIN 1988-300) define

• standard temperature regimes [e.g. for DIN 1988-300 : 15°C (cold water) - 60°C (hot water)]

• standard flow rates for tapping points [e.g. for DIN 1988-300 : V_DHW = 0,15 l/s]

Let’s take the example of the shower for DIN 1988-300.

standard regime

With the temperature regime as defined by the standard, the shower tap flow would result in 0,15 l/s @60°C and 0,15 l/s @15°C
This results in an overall flow of 0,30 l/s @ 37,5°C. That’s the “goal situation“ we want to design to.

custom regime

Suppose the designer wants to deviate from the standard, and wants to apply a custom temperature regime, e.g. 10°C - 50°C.
If we don’t change the hot water flowrate, we will not be able to reach this “goal situation” without exceeding a hot water flow rate of 0,15l/s : we can reach 0,30l/s @ 30°C or we can reach 0,27l/s @37,5°C, but we cannot reach 0,30 l/s @ 37,5°C.

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Recalculation

If we don’t change the design flow rates, we will not be able to reach the design “goal situation”.
How can we realize the same goal with the regime of the satellite unit : 10°C - 50°C ?

The equations we have to solve for the example to reach the same goal situations are :

• V_DHW + V_DCW = 0,30 l/s

• 50°C * V_DHW + 10°C * V_DCW = 37,5°C * 0,30 l/s

In a more general way, these equations end up in a recalculation of the hot water design flow to :

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