[TRNSYS-users] Water-to-water heat pump - Heat rate to load control

[David BRADLEY]

Damien,
   In my experience, there are relatively few heat pumps available on 
the market that can do what you are trying to do. Most heat pumps have a 
fairly fixed capacity (some have multiple stages) so that they have an 
easier time maintaining a fixed temperature rise than they do in 
maintaining a fixed temperature outlet. There is at least one notable 
exception to this; an air-to-water heat pump that has a variable speed 
compressor that allows it to modulate and maintain a target outlet 
temperature.

   Type927 is a temperature level control device meaning that it is 
looking for inlet water conditions on both sides and for a control 
signal. If you have obtained your heating loads from some other software 
tool, I would recommend that you read them into TRNSYS using Type9 and 
impose them on a water stream using Type682 from the TESS Loads and 
Structures library. I would then place a thermostat sensing water return 
temperature in the loop and I would use its output to turn on the loop 
pump and the Type927 heat pump. You will not get a constant supply 
temperature of course but in reality, a single stage (or even multi 
stage) heat pump can't really give you a constant supply temperature; it 
can only give you a supply temperature that hovers around a set point.

   If you are using Type56 to generate your building's heating demand, I 
would take it out of energy rate control (ie turn OFF the automatic 
heating and cooling types in TRNBuild), and allow the zone temperatures 
to float. I would then use a thermostat watching the zone air 
temperature and some kind of delivery device (a fan coil, radiant 
floors, etc.) to deliver the hot water from the Type927 to the zone.

Kind regards,
  david


On 6/6/2012 12:20, Damien Casetta wrote:
> Hi,
>
> I am trying to handle this problem by controlling the temperature. Let 
> me remind you that I want to control the heat load of an heat pump in 
> heating mode.
>
> Here is how I am trying to proceed :
>
> - I control the temperature exiting the heat pump
> - I fix a temperature set point (with an aquastat - heating mode) at 
> 50 C.
> - I vary the supply temperature (entering the heat pump) according to 
> the heating demand.
>
> The heating demand is based on hourly loads.
>
> What do you think about it?
>
> I am not very satisfied but I will give it a try. I am sure there is a 
> much simpler way to do it.
>
>
> Thanks in advance for your help.
>
> Best regards,
>
> On 1 June 2012 18:10, Damien Casetta <damien.casetta at gmail.com 
> <mailto:damien.casetta at gmail.com>> wrote:
>
>     Hi,
>
>     I am modelling a ground-source heat pump system including a
>     water-to-water heat pump (type 927), a borehole heat
>     exchanger (type 557b) and a building demand profile.
>
>     I have read a couple of messages in the archives about this topic
>     but I haven´t understood correctly the few addressing my specific
>     issue.
>
>     Here is my point. I assume the heat pump to meet the building
>     demand. The aim is then to force the heat pump load and observe
>     how the system behaves (COP, ground loop fluid temperatures).
>
>     I would be able to do this with an external MATLAB code (with COP
>     values interpolated from catalog data) but it would be a shame not
>     to harness TRNSYS potential (there is no need to re-invent the
>     wheel as I read in a previous message).
>
>     Let me put in other words: how to control a heat pump load?
>
>     I have read about a trick to handle this, with a "lump"
>     temperature but I don't get the idea behind it. Any other
>     explanations is welcomed.
>
>
>
>     Thanks in advance,
>
>     Best regards,
>
>
>     -- 
>     *Damien Casetta*
>
>     *Chalmers University of Technology *| Energy and Environment|
>     Exchange student
>     *INSA Lyon* Génie Energétique et Environnement | Elève ingénieur
>
>     +46.7.60.66.31.45 <tel:%2B46.7.60.66.31.45>
>     +33.6.71.78.03.75 <tel:%2B33.6.71.78.03.75>
>
>
>
>
> -- 
> *Damien Casetta*
>
> *Chalmers University of Technology *| Energy and Environment| Exchange 
> student
> *INSA Lyon* Génie Energétique et Environnement | Elève ingénieur
>
> +46.7.60.66.31.45
> +33.6.71.78.03.75
>
>
>
> _______________________________________________
> TRNSYS-users mailing list
> TRNSYS-users at cae.wisc.edu
> https://mailman.cae.wisc.edu/listinfo/trnsys-users

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

P:+1.608.274.2577
F:+1.608.278.1475
d.bradley at tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com

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