In Tank Heat Exchanger and Rennai Backup

[Hunderliggur]

Looking for comments. Last season I used the 2x500 storage tanks as a very big radiator in my unfinished basement. This helped the first floor a lot, but not so much for the second floor. I am now adding an in tank heat exchanger. The control logic will route the return water through the heat exchanger if the storage temp is greater than the floor return temp. Separate logic will bypass the Renai if the heat exchanger output is greater than 130F (because of the high head loss in the Rennai and to minimize wear and tear on the Rennai system). The radiant zones are controlled by a discrete radiant controller which starts the zone pump and the system circulator. Domestic Hot Water cold water make-up is run through the radiant tubes (to prevent stagnation in the floor during the summer) before being heated for domestic use (I know it is wierd, but it really does work well). I have omitted balancing valves, drains, vents, expansion, etc. for clarity (and time). Any comments or suggestions are appreciated.

 

[heating8]

YIKES ^2

Unless you're a professional plumber, please don't try this.

1. domestic make up through your heating system isn't a good idea. You've got to have the correct EVERYTHING to deal with the oxygen, chlorine, minerals, and that's assuming everything else is brass (including circulators) and you're using the correct pex etc. etc. etc.

2. why not set the rinnai and forget about all the additional valves. How are you getting flow through it in summer when you're not running the boiler? Just set the temp you want and it will come on as needed (depending on age of the units and model) just watch your minimum turndown ratio. Make sure you have mixing valve (to prevent scalding somewhere)

3. water takes the path of least resistance, so the amount of flow through your pex heating is almost nothing in the summer (yes i know the drawing isn't to scale.

4. why the circulators in series (1,2,3 & c)? Unless there's a reason, just pipe C in parallel and dump all the other valves you're adding to the right side of the drawing.

 

[Hunderliggur]

1. domestic make up through your heating system isn’t a good idea. You’ve got to have the correct EVERYTHING to deal with the oxygen, chlorine, minerals, and that’s assuming everything else is brass (including circulators) and you’re using the correct pex etc. etc. etc.

Original radiant system was designed by the Radaiant Floor Company and has been working well. Parts are as you describe. Fortunately, we don't have any chlorine, we actually have GOOD well water.

2. why not set the rinnai and forget about all the additional valves. How are you getting flow through it in summer when you’re not running the boiler? Just set the temp you want and it will come on as needed (depending on age of the units and model) just watch your minimum turndown ratio. Make sure you have mixing valve (to prevent scalding somewhere)

DHW input for the Rennai comes from the pressure system (not shown, but are Grundfos constant pressure pumps from a cistern. We have a low power well pump that fills the 1500 gallon below ground cistern and the pressure pumps give us high flow/high pressure when we need it on the farm, like filling an animal trough with 100 gallons of water). I can set the Rennai at 130F and the mixing valve from storage will keep the Rennai input at 135F or less. The Taco valve with the differential control will use stored heat (even in summer when heated from future solar or when I build a fire) if the storage is hotter than the return/makeup temp.

3. water takes the path of least resistance, so the amount of flow through your pex heating is almost nothing in the summer (yes i know the drawing isn’t to scale.

The flow through the radiant is the makeup for DHW in the summer. Not a lot of flow and yes, it will take the path of least resistance. I can manually bypass the radiant if needed with valves not shown.

4. why the circulators in series (1,2,3 & c)? Unless there’s a reason, just pipe C in parallel and dump all the other valves you’re adding to the right side of the drawing.

Circulators 1, 2, and 3 are the independent zone controls. You're right, I don't need C (unless the head from the in tank HX is too high which I don't believe it will be). I can add that circulator later if needed.


Thanks for your inputs, I do really appreciate them. See if this revised drawing is better.