Re: tempering valve for heating

[Michaël Kummert <kummert@xxxxxxxxxxxxx>]

Susanna,

> I would like to know if in TRNSYS lybrary exists a tempering valve for
> heating. Until now I have only seen tempering valves for cooling a fluid. If
> not, could you give me a tip for heating water with a valve.
I am not sure to understand your question.I can think of two "modes" for 
a tempering valve:
1. You control the temperature of a mixed flow by adjusting the amount
   of "cold" fluid that bypasses a heat source. This is what typically
   happens in a heating application, e.g. domestic hot water.
2. You control the temperature of a mixed flow by adjusting the amount
   of "warm" fluid that bypasses a cooling device (e. g. a cooling
   coil). This would happen in a cooling application.
Type 11 (Type11b in IISiBat) can be used in case 1, so I assume you are 
looking for a solution to case 2. The name "tempering valve for heating" 
is somewhat confusing.

Assuming you want to solve case 2, Type 11 cannot be used and I think 
the easiest solution is to use equations to set the different flowrates 
in your system. Assuming you have an inlet flow (m_tot, T_in) that you 
want to send to a cooling device (flowrate: m_cold, Temp.: T_cold) or to 
a bypass (m_bypass) to obtain the desired temperature (T_set) for the 
mixed flow, you can use the following equations:

m_cold   = m_tot*(T_in - T_set)/(T_in-T_cold)
m_bypass = m_tot-m_cold

Besides the fact that equations are probably less easy to use than a 
component, some problems could occur:

- You do not have a way to prevent numerical oscillations (which is done
  with parameter 2 of Type11b in the "heating" case). So you will have
  to be careful and check that TRNSYS converges during the simulation.

- The above equations will obviously not work if T_in=T_cold or if it is
  not possible to reach the setpoint. In that case, Type 11 would just
  send the entire flow stream to one branch, but the equations will lead
  to an error. If you get that kind of problems, you will have to use
  tricks to prevent them (e.g. tests using the GT function, like adding
  a very small value to the difference if it is zero)

TRNSYS 16 will have a component equivalent to Type11 for "cooling 
applications".


Kind regards,


Michaël Kummert


--
_________________________________________________________

Michaël Kummert

Solar Energy Laboratory - University of Wisconsin-Madison
1303 Engr Res Bldg, 1500 Engineering Drive
Madison, WI 53706

Tel: +1 (608) 263-1589
Fax: +1 (608) 262-8464
E-mail: kummert@engr.wisc.edu

SEL Web Site: http://sel.me.wisc.edu
TRNSYS Web Site: http://sel.me.wisc.edu/trnsys