Solar Hot Water, Rainwater & Condensate Lab
Size a solar hot water system: daily hot water, storage, collector area for your solar fraction and the back-up heater. Then size a recycled water tank fed by rainwater and AHU condensate, month by month, and see how much mains water it saves. In the Gulf the condensate usually beats the rain many times over.
How to use: pick a city to load climate data, then set the building. Every field has an i with a plain explanation.
2. View
3. Checks
4. Monthly figures
5. How it works
Solar hot water
Daily heat = hot water volume × 4.19 kJ/kg K × (60 °C − cold water temperature). Solar collectors deliver about the daily irradiation on the collector × system efficiency, so the collector area is the solar share of the heat divided by that yield. The worst month sets the area if you want the target all year, the average if annual is enough. Dubai's Al Sa'fat requires solar water heating for a large share of domestic hot water in many building types.
Back-up and Legionella
Store at 60 °C and distribute at 50 °C or more so Legionella cannot grow. The back-up heater must reheat the store within the recovery time on a cloudy day.
Rainwater and condensate
Rainwater yield = roof area × rainfall × runoff coefficient. Condensate from AHU cooling coils = air mass flow × the moisture removed. In humid Gulf summers each 1,000 L/s of fresh air can give close to 1 m³ of clean, cold water a day, at exactly the time irrigation demand peaks.
Learning and checking tool. Climate figures are typical long term averages. Use project data and the authority's rules for recycled water treatment and labelling.