Hi Raghad,
You've brought in a challenging one! I've found eQuest's options for modeling ground to water heat pumps limited, and I've had to use workarounds in the past. Here's two ideas; I'm assuming you have some experience with eQuest's detailed interface.
The simple way is to use water-to-air heat pumps (like a PTHP system) and add the pumping power from the 2-pipe loop to the ground loop. A possible disadvantage of this is that it might overestimate pumping energy if the 2-pipe loop ever turns off while the ground loop operates continuously, which it might do to provide some freeze protection. Another possible disadvantage is that this will allow the system to address simultaneous heating and cooling loads, which a 2-pipe system can't do. However, if you're doing a small residential building simultaneous loads probably won't be an issue.
If you really want to create a true water-to-water system, I'm afraid it's a bit more complicated:
- Create a 4-pipe fan coil system in the wizard. Go to the chilled water plant and make sure that you select a water-cooled condenser.
- Switch over to the detailed interface. Change the loop type of the condenser loop from a condenser loop to a water-loop heat pump loop. Create a ground heat exchanger, assign it to the loop, and delete the cooling tower. One important thing: when you change the loop type to a water-loop heat pump, go to the "Controls" tab and change the "Min Alarm Temp" field (which is in the bottom left) to the lowest temperature you expect to come from the ground heat exchanger.
- Open up the chilled water loop and change it to a 2-pipe loop. Open up your chiller and change it to a heat pump. DO NOT edit the "CW Loop" field (which will now be blank). eQuest technically only allows the heat pump "chiller" type to connect to a lake/well loop, but for some reason eQuest is "fooled" if you don't try to assign the loop yourself.
- Delete the hot water loop pump, any boilers attached to the loop, and the hot water loop itself. eQuest will prompt you to reassign some components - assign them to the 2-pipe loop you created in the last step.
Good luck!
Drew
