Quick question:  I am sure there will be a few opinions.

3T W-W system.  Only used for heating.   Have a zone feeding a 40 gallon pre-heating tank for my 60 gallon electric domestic HW.    Once heating is done (no A/C), should I utilize the GSP to continue to pre-heat?   2 people in the house.   I think it is not worth it to bring 40F water up to 110F water in the off season.   The cost of juice here is approx 15cents/KWH.

Or I guess I could install a solar HW system..    the payback math re this option does not compute

Cheers

Fred

I would think YES!! Making 110* water with a COP of 2 1/2 maybe better. Then finishing the last 10 or 20 degrees with electric tank.

ChrisJ

Here is a system that uses the GSHP to provide all of the domestic hot water:

http://www.ourcoolhouse.com/monitor/monitor.htm

Yes why not a DHW zone vs dsh....are you open or closed loop

Good question.    The DHW has a pre-heat tank and does have a zone and a thermostat.   Currently set to kick in when the water is 90F and off at 100F.   It is also passively heated (it was set up to always be topping up when the GSHP is running.   However,  it has its own pump and is connected to my GSHP's buffer tank.  I do not have the Desup hooked to it.  The desup is hooked to the baseboard zone to push higher temp water into that area.

Closed loop-  2 x 270 foot wells into granite

http://welserver.com/WEL0383/



Why not making 100% of your hot water via the geosystem? heat exchanger is required. See link.

Doc

Very interesting link.    Similar incoming and outgoing loop temps as I am seeing out here in Nova Scotia.    My pre-heating tank for my DHW does have the inner coil being fed off my buffer/GSHP so I guess it is a heat exchanger unit.   I could easily heat the water to 110F.  Couple of questions.   Do these people not top up their DHW temp?   110F to me seems not hot enough for our showers..  perhaps it is.

Over the past three non-heating seasons I power down my GSHP system and tanks.    I am intrigued if the economics suuggest I utilize the system throughout the year.

Fred

Anti Scalding law in New York State requires temp at the faucet to be below 120F, residential code requires it to be at 110F minimum. Heat exchanger must be at certain minimum size to allow heat transfer into the tank, we design for 8 F delta T, meaning 128F supply will result in 120F tank temperature. So we set them at 115F with 10F differential, meaning it keeps the tank between 110F and 120F. Sometimes lower with elderly customers, by code we cannot go higher than 110F in nursing homes or hospitals, or in homes with young children. 120F can cause 1st degree burning.
Works well with stiebel-eltron tanks where we connect both heat exchangers. No top off needed.
Here are a few more.
http://welserver.com/WEL0267/
http://welserver.com/WEL0664/

Doc- again thx forthe links. interesting. You have GSHP supplying baseboards at 150F? I have those in 1 zone and the temp is nowhere near that. Would love to hear how that happens. diff thread...

Onto the main topic. I guess it makes sense to keep a buffer tank sitting at 108F to supply my pre-heat DHW tank? I am now wondering if I should use a different cut in, diff temp . right now 108F, temp diff of 10F.. while the system runs the buffer tank seems to hover at 90-91F until the floors get to temp. The actual water leaving the pump is approx 101F

Fred

Large heavy radiators (like slab floors) will quickly drag down the temperature of a buffer tank unless you use a mixing valve. Good for efficiency, not so good for DHW.

Posted By Fred2010 on 09 Apr 2013 02:13 PM
Doc- again thx forthe links. interesting. You have GSHP supplying baseboards at 150F? I have those in 1 zone and the temp is nowhere near that. Would love to hear how that happens. diff thread...

Onto the main topic. I guess it makes sense to keep a buffer tank sitting at 108F to supply my pre-heat DHW tank? I am now wondering if I should use a different cut in, diff temp . right now 108F, temp diff of 10F.. while the system runs the buffer tank seems to hover at 90-91F until the floors get to temp. The actual water leaving the pump is approx 101F

Fred

This is the main topic. Once you have a W-W with a large heat exchanger, you can run the DHW as an independent zone. All you need is a 3 way valve and a heat exchanger, and 2 boiler controls to set the DHW at a different setpoint than your buffer tank. So it prioritizes on your DHW to whatever you set your boiler control, heats it up, and then switches over again to your hydronic buffer tank controlled by the outdoor reset. That way you have your DHW at whatever you set your temp at all year around, and your efficient low temp heat for your radiant floors for winter only.