# [TRNSYS-users] Problem of Type 917 and water temperature simulation

Fri Jul 12 08:40:04 PDT 2013

```Jing,

> I am modeling a building using water to air heat pump. I am using type
> 917 and I have several questions:
> 1. When I use buried horizontal pipes and ground Vertical U-tube in
> GHP library, how could I simulate the ground variables? Like the local
> water flow temperature, soil temperature. etc. TMY2 doesn't provide
> with such data.
the soil properties usually come from having done a test bore (unless of
course the project is theoretical in which case you will have to use
ground properties that you find in reference materials. You can get
estimates of the average ground temperature, the amplitude of the
ambient temperature swing, and the day of the minimum ambient
temperature by plotting results from the TMY file. The ground water flow
is very difficult to estimate. I suppose that what I would recommend is
to run your simulation with a few different values of ground water flow
rate to see how much the simulation results are impacted by your
assumption.
> 2. Could buried horizontal pipes and vertical U tube be used together?
> Just simply connect their inlet and outlet flow rates will be correct?
there should be no problem doing this.
> 3.If I connect vertical U tube with horizontal pipes, should I have
> different size horizontal piples to cater the flowrate accumulation of
> the U tube in series? For example, the horizontal pipe with one U-tube
> is 1/4 and the pipe with two U-tube will be 1/2 . But if I put some
> many type 952, I guess my model will be messed up. Is there any
> solution for that?
I am not entirely sure that I understand your concern. The models are
only looking at the thermal aspect of the problem. The tube diameters
are used in calculating the pipe surface area, not for any pressure loss
calculations. I also don't know what configuration you are looking at
but you may be able to use a single instance of Type997 instead of many
instances of Type952.
> 4. What's the major difference between type 917 and 919  ?
Type917 models an air-to-water heat pump where the air is the source
side. Type919 models a water-to-air heat pump where water is on the
source side.

Kind regards,
David

--
***************************
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370