I am using TSOL with configuration A7.1 - DHW thermosyphon system with electric water heater to model a thermosiphon system. In the simulation report, I am trying to understand what "DHW heating energy requirement" and "Annual energy requirement" represent.

Observations:

• For large loads, both values are displayed and are equal, and in some cases they are different but nearly equal

• For smaller loads, the "DHW heating energy requirement" disappears from the report entirely. Only "Annual energy requirement" remains

My questions:

1. What do these two fields actually represent? The difference does not appear to be losses, since losses are reported separately elsewhere in the report.

2. Why does the "DHW heating energy requirement" field disappear for lower loads? Is there a threshold (e.g., solar fraction > 95%) that changes the report format?

Thank you for any insights.

Dear Koffi,

Thank you for your inquiry.

Demand and supply are only shown separately if there is a shortfall. If both are the same, everything is covered, and only one value is displayed.

Example 1: Small storage tank without heating element

Demand = 2635 kWh/year
Solar energy supplied to storage tank = 1413 kWh/year
Storage tank supplied to domestic hot water = 1282 kWh/year

1400 kWh shortfall

Example 2: Small storage tank with small heating element

Demand = 2635 kWh/year
Solar to storage tank = 1158 kWh/year
Heating element = 1562 kWh/year
Storage tank to DHW = supplied 2342 kWh/year

There is still a shortfall of approximately 300 kWh, therefore "Requirement" is also displayed.

Example 3: Large storage tank with large heating element

Solar (1230) + Heating element (1996) = Energy consumption (3226 kWh)
Energy consumption (3226) – Storage losses (592) = Energy delivered (2634 kWh)

The "Requirement" value is no longer displayed, as the demand has been met.

If you have further questions, please let us know the exact TSOL version and send us screenshots and, ideally, the project file (*.tsprj).