Re: [TRNSYS-users] Ventilation VS cooling & heating

[David BRADLEY <d.bradley@tess-inc.com>]

Chou,
  In Type56/TRNBuild the term "VENTILATION" just means a flow of air whether it is hot, cold, or neutral. It isn't necessarily tied in any way to the HVAC system. The "HEATING" and "COOLING" types are used to calculate sensible loads for the space. Those types don't have anything to do with how that energy is delivered to the space.

  Typically, there are two kinds of simulations that I do with Type56:

Early on in a project, I need to determine the peak heating and cooling loads for the space and I need to get a very basic idea of how much energy the building will consume over the year. In order to do this, I use VENTILATION types to put the outdoor (fresh) air requirements into the zone. and I use HEATING and COOLING types to define set points. I allow the "system" to have unlimited power because all I really care about is the maximum hourly value and the annual sum. The annual sum gives a very rough idea of how much energy is required by the building. You have to do one of two things in order to get how much energy is required by the HVAC system: either define a simple COP for the heating and cooling system or use other TRNSYS models that take heating and cooling load as an input and return the power consumed (note, there are very few of these components)

The second kind of simulation is much more common and gets at one of TRNSYS's strengths. In this, you use the VENTILATION type to deliver hot or cold air to the space and you use a thermostat model (such as Type108) to turn on and off equipment that controls the flow of air. In this case, you disable the HEATING and COOLING types because you don't care about loads. The equipment of the system (fans, pumps, heat pumps, furnaces, chillers, etc.) will compute their source energy requirements as a function of their inlet conditions and the building will simply react to the ventilation air that it receives.

Kind regards,
 David
 

On 12/18/2011 05:12, Chou Shen wrote:

Hi

Thanks to David and Matt, you messages have helped me a lot. Now I know how to use type 24 & 25 to get monthly summary.

At this time I have some other questions:
1. When Editing type 56, in the Ventilation lable, the Heating and Cooling option can be set up by defining airchange rate and temperature & RH of air flow; while in both the Cooling lable and Heating lable, the cooling and heating option can be set up by defining cooling / heating power (does that mean I need to estimate the cooling / heating load before set this block up?), and the setpoint temperature & RH. As a result, type 56 provides two methods to define HVAC system. What's the relationships between the two methods?.

2. In addition to adding the information of HVAC in type 56, do I need to creat the HVAC system in to get the information of energy consumption of HVAC system?

Thanks!


--
Chou Shen
Graduate Research Assistant
Department of Civil, Architectural & Environmental Engineering
Missouri University of Science and Technology

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***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI  53703 USA

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