How can I model swimming pool gains?
The approach I recommend for modelling gains from swimming pools is as follows.
1. Sensible heat gain. Represent the body of water as a room, maintained at a constant temperature. Represent the surface of the water as a window, consisting of a single pane with properties: transmittance=1, absorptance=0, reflectance=0, refractive index=1. This takes care of the sensible gain from the pool to the space above it. The software will of course generate a load for heating the pool, which you can either use or ignore depending on the aim of the study.
2. You will need to set a low surface resistance for the construction representing the downward-facing side of the surface. Do this in APcdb by unticking the default box for either Inside or Outside Surface Resistance (as explained below) and typing in the value 0.01 m2K/W. You need to decide whether the downward-facing side is 'inside' or 'outside' by applying the convention that the inside surface is the one facing the room that appears first on the ModelIT browser. When you've made this change you'll see surface temperatures close to those for the pool water.
3. Latent heat gain. Evaporation of pool water constitutes a latent gain to the space above. The software will not calculate this for you, but you can estimate it. An accurate estimate of this gain would take account of the vapour pressure difference between the pool (saturated) and the air, as well as the area of the pool surface (corrected for waves) and the area of wetted surfaces around it. Some of these parameters are difficult to estimate, and I recommend you use figures provided by equipment manufacturers. A number of these can be found on the web, and this one from Desert Aire is useful (see Table 3): http://www.desert-aire.com/index.php?option=com_docman&task=cat_view&gid=128&Itemid=179&mosmsg=You+are+trying+to+access+from+a+non-authorized+domain.+%28www2.iesve.com%29
