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Investigating Effectiveness of your HVAC System Using SOLIDWORKS Flow Simulation
  • Investigating Effectiveness of your HVAC System Using SOLIDWORKS Flow Simulation

    Posted on May Mon, 2016 by seacad_admin

    The design and installation of HVAC system is getting much more complex compared to yesterday-years. It was used to be that you choose your HVAC unit, and place it wherever you want. But with the current trend of going green and creating buildings that are eco-friendly through less power consumption, designers are pushed to come up with creative ways to make a HVAC system that is both effective and efficient. In fact, Singapore makes it an accreditation by giving out BCA Greenmark certifications to company that meets the requirements. Special grants are also provided for vendors meeting such requirements.

    So what can a designer do to make their HVAC set-up not only meet customer’s requirement but also in such a way that energy consumption is at its lowest? Let’s look at a scenario as below:

    Here we have a typical Hospital Room with a patient and a doctor. On average we can expect about two person at a time that will be in the room. The common sources of heat would thus be:

    1. Metabolism from people
    2. Lights
    3. Electronic Equipment that are expected to be in operation

    A logical location for an air-con system would be from the center of the room, so that the cool air would travel evenly around the room. However we don’t know if the patient inside would be comfortable being directly under the air-con. We could put it away from the patient, but would the patient then feel warm? So let’s first vary the position of the air-con. Here we have set-up 5 potential locations:

    Doing a quick study in Flow Simulation for position number 1, we would get the following results:

    This is a temperature plot across a certain area in the room. Here we see that the patient experiences temperature between 35°C to 28°C across the body. But now the question is, is he comfortable?

    Temperature profile is not the best way to evaluate comfort, because what is cold for someone may be warm for others. That is why specific terms has been designated to measure such sensations, such as:

    • Predicted Mean Vote (PMV) – is an index that predicts the mean value of the votes of a large group of people on the 7-point thermal sensation scale.
    • Predicted Percentage Dissatisfied (PPD) – is an index that establishes a quantitative prediction of the percentage of thermally dissatisfied people determined from PMV.

    A PMV is a value between 3 to -3, with the optimum condition being at 0. So lets have a look at the PMV plot for Position 1:

    Here we see that the PMV varies about 1-2, which indicates that the patient is feeling uncomfortable due to warmth. With a quick re-run of the analysis on the different locations, we get the following results:

    Location 2

    Location 3

    Location 4

    Location 5

    Here we see that the location 5 is the best location for the air-con to cool the room. This knocks out one variable. If we want to achieve better PMV values, we can then vary the inlet temperature of the air, mass flow rate, location of heat sources and many other variables until we get our best outcome. All these can be done in hours!

    This removes the guess work when it comes to designing the HVAC system, and to enable us to reduce power consumption due to more efficient design. If you would like to know more about SOLIDWORKS Flow Simulation and its HVAC capabilities, feel free to contact us at +65 6372 1416 or email marketing@seacadtech.com.

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