Issue with seperate hot and cold water pumps...

[joeborg]

Hi,
I'm dealing with a slightly complicated scenario. Essentially, my parents and I will be living in the same building; I'll have an apartment and they'll have the penthouse above me. For cost saving reasons and to save on roof space, our intention was to have a shared Solar Water Heater (SWH) supplied by water from a well we own. We'd then have two separate cold water feeds. In order to do this, I thought we could work using three water pump:

- 1 pump between the well tank and the SWH that would feed hot water to both of us (there's a T joint in the piping just after the solar water heater with one end going to my apartment and one end going to the penthouse).
- 1 pump on my cold water mains supply to my apartment
- 1 pump on the cold mains supply for the penthouse.

This essentially means there will be two pumps feeding each home. The (common) hot water pump for hot water and the cold water pump for cold water.

The problem we're having is that, at shower/bathroom mixers, there seems to be no gradual change from hot to cold water and viceversa. It's as though either hot water or cold water comes out. The explanation we've been given so far is that, due to the fact that we're using two separate pumps to feed hot and cold water, the pumps essentially end up 'competing' against each out. If one pump is on, there isn't enough flow/pressure for the other pump to also activate.

Given this situation, I was wondering if anyone had any thoughts on the above? Is it not possible to have two separate pumps? If so, what could the problem be? If not, is there any other solution that would allow us to share the solar water heater that you can think of?

Thanks,

Joe

 

[chris watkins]

More info required Joe, what type of pumps are being used (I am going to guess they are positive type). Why is it not possible to have one pump set to feed both hot & cold = equal pressures ??

 

[joeborg]

Hi,
Apologies. I'm not a plumber myself so I'm not sure I'm using all the right technical names. That said,

- This is the pump used for the hot water: Coelbo Speedmatic Easy (I tried to post a url to the datasheet but it won't allow me). It's an inverter based pump with a pressure switch (so it should be negative head if I understand correctly).
- The cold water pump is a normal pump that originally had a flow-switch (positive head). That said, we've now changed it to a pressure switch (negative head?) and that made no difference.

Both pumps as set to 3.0bar.

As for why we can't use one pump, the problem is that we have separate cold water supplies so, if we are to share hot water supply but have separate cold water supplies, we can't make do with just one pump for both homes.

Thanks for looking into this. I really appreciate it.

Joe