Hi all,
Currently working on a waterpark with VE, I would like to model the evaporation from the indoor pools in order to assess properly the impact on relative humidity and dehumidification energy consumption.
I have calculated the amount of water evaporated (function of inside temperature, water temperature and relative humidity) using mathematical correlations found in literature. My problem is now to model it in VE. I have used 2 approaches so far:
1 - Convert the amout of water evaporated (kg/h) in latent heat (kW) using the Internal gains in Apache. This method is too basic because I have to assume that the evaporation will be roughly constant as it cannot depend on room temperature. I created a variation profile with a night value and a day value, but it is still too simple.
2 - Creating a fictive humidification system using ApacheHVAC. The idea is to extract a certain quantity of air from the room, to heat it at room temperature, to humidify it at 100% RH and to introduce that air back in the room. That way, I can control the amount of water introduced to the room based on RH, but I still assume the room temperature is constant.
Those 2 methods give really different results on room conditions. Does anyone have ever dealt with that problem? Is there one "known" approach with VE?
Thanks a lot for your answer !
Cheers,
David
Modelling water evaporation from a pool
-
MatthewSteen
- VE Graduate
- Posts: 51
- Joined: Mon Nov 17, 2014 5:43 pm
- Location: Denver, CO, USA
Re: Modelling water evaporation from a pool
Old post, but here's recent info from the IES VE Support FAQ
http://www.iesve.com/support/knowledgebase/faq/2116
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?op ... sve.com%29
http://www.iesve.com/support/knowledgebase/faq/2116
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?op ... sve.com%29
Building Performance Engineer | Ambient Energy | http://ambient-e.com/
Q+A Resource for the Building Energy Modeling Community | https://unmethours.com/questions/
Q+A Resource for the Building Energy Modeling Community | https://unmethours.com/questions/
Re: Modelling water evaporation from a pool
Curious what approach you ended up with. Your first approach to model the evaporation as a Latent gain to the space with a profile is not a bad idea. There is an On demand learning video from IES that recommends doing it this way. Most of the times, 'simple' works pretty well.
You should have two evaporation rate - one during occupied period (activity factor > 0.5 usually) and one during unoccupied period (activity factor ~ 0.5?). If you know how the pool is going to be occupied, you can put this on a variation profile. This will get you 85% there. You can go in the weeds to model the physics accurately, but engineering judgement is needed. What is your goal and is the project budget big enough to accommodate the extra ~15% work.
You should have two evaporation rate - one during occupied period (activity factor > 0.5 usually) and one during unoccupied period (activity factor ~ 0.5?). If you know how the pool is going to be occupied, you can put this on a variation profile. This will get you 85% there. You can go in the weeds to model the physics accurately, but engineering judgement is needed. What is your goal and is the project budget big enough to accommodate the extra ~15% work.