[TRNSYS-users] Air source heat pump system validation

[David BRADLEY]

Zhe Li,
   I look at similar energy balances quite often so I suspect there is 
not a systematic problem but something wrong in the simulation. There 
are a few things to look at.

First, make sure that you have some thermal capacitance in the liquid 
loop. This will usually take the form of a buffer tank. The tank should 
have enough volume to store at least one timestep of liquid at whatever 
flow rate your pump is running.

Second, look at the controls on your flow loop. Type941 is basically an 
ON/OFF device; it does not meet a set point temperature but simply puts 
its entire current capacity into cooling down (or heating up) the liquid 
loop. Under low load situations, this can dramatically overheat or 
overcool the liquid loop; the tank above should help this a lot.

Third, make sure that you are using a reasonably short timestep (1 or 5 
minutes). this will allow your system to be controller appropriately.

When you look at the energy balance, you have to also look at the 
beginning and ending temperature of the liquid loop. If it is 
significantly different than it was at the simulation start, you have to 
account for stored energy in your balance.
Kind regards,
  David



On 10/16/2012 08:42, Zhe Li wrote:
>
> Dear TRNSYS users,
>
> Thanks for your time.
>
> I am currently performing a simple validation of an air source heat 
> pump system. The air-source heat pump is Type941, and I am using a 
> defined thermal load (Type682) with an input file (Type9). However, 
> the results I am getting for the Total Heat Transfer to Liquid from 
> output option in air source heat pump component is between 2 and 3 
> times higher than the Heating Load Met from output option in thermal 
> load. I cannot think of any reason why the generated energy is 
> significantly higher than the load met.  I would understand if the 
> generated energy is a bit higher than the load met as there might be 
> heat losses from connected pipes.
>
> Could anyone give me some advices? This is very important for me to 
> continue my research project.
>
> Thanks very much in advance.
>
> Zhe Li
>
>
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-- 
***************************
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
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