DHW Flat Plate HX with Taco 008VDT

billyboy

Think this will work for DHW?

Instead of usual flow switch to turn on pump, use VDT sensors.

I know that there will be a small heat loss pipes HX etc.

billyboy

Hatt, Cool idea

As I already have the GEA FPHX & Taco 008VDT I'm looking to use them.

I used 130* return just to make the BTU's balance at 100,000

I would probably set 008VDT DT knob to 5* to get quick response. The return temp. would vary based on DHW current useage.

billyboy

I will use a Taco 003 with a Fenwal thermal switch for DHW recirculation.

I will keep the 008VDT powered up, with heat request jumpered on, it will use very little power (63ma) & keep the HX hot.

DIP switches:
#5=off, linear
#4=on, fast response
#3=on, reverse mode: DT gets smaller -> pump slows,
DT gets larger -> pumps faster
#2=off, minimum speed = 8% .08 x .79A = 63 milliamps
#1=on Delta T mode

S2(source) HX in,
S1(load) HX out

billyboy

Hatterasguy said:

If you set it to 5, it acts like a fixed (high speed) pump.

Where did U get that info?

billyboy

This is my GEA HX
It's ovesized vs this printout requirement

billyboy

Here is a GEA simulation printout showin that it can move 126MBH

billyboy

showing, I'm not that redneck

billyboy

There is a common misconception about FPHX efficiency.

They are not inefficient just because the output may be 25* lower than the input.

Those BTU's don't evaporate in the HX, they return to the input source.

Only heat lost is from surfaces, even the pumps electrical energy is not wasted inside a heated structure in winter. (COP = 1)

billyboy

With no DHW use the DT would be about zero.
When DHW use starts, I want the pump to ramp up quickly.

Use 10* or 15* DT setting ?

Possibly VDT has different DIP switch control than VS ?

" (in normal mode)" R U talking about DIP Switch 3 ?

If so, Taco says not to use Normal Mode on VDT

#3=off, normal mode: DT gets smaller -> pumps faster,
DT gets larger -> pumps slower

billyboy

Wow, I thought that I was alone in not making sense of this, Thanks, now I don't feel so dumb.

Rich_49

http://www.taco-hvac.com/uploads/FileLibrary/102-143.pdf

http://www.taco-hvac.com/uploads/FileLibrary/102-359.pdf

The manuals are here .

Rich_49

That's crazy . I had trouble posting last night or yesterday , they would not post . Logged on this morning and I guess they popped up

billyboy

Lots of info here using flow switch:

http://www.pmmag.com/articles/95060-sidearm-revamp

billyboy

Siggy is suggesting 117,650 btuh through 5x12x30 at 3.62 gpm in DHW side.

"Instant benefits
Here’s a summary of the benefits offered by this method of instantaneous domestic water heating.

1. It’s readily adaptable to thermal storage tanks of various sizes and heated by a variety of heat sources.

2. Suitable brazed-plate, stainless-steel heat exchangers are available from several manufacturers. If local codes insist upon double-wall heat exchangers, they also are available.

3. The external stainless-steel heat exchanger can be easily inspected, cleaned and replaced if necessary.

4. The thermal mass of the storage tank stabilizes domestic hot water delivery temperature during long demand periods. This helps eliminate fluctuations in delivery temperature.

5. In the case of a solar drainback system, this approach eliminates the need for any internal heat exchangers in the storage tank. This allows a wider choice of potential tank suppliers.

6. The standby heat loss associated with a separate DHW storage tank is eliminated.

7. The warm-up time of this assembly is very short, significantly shorter than that of a gas-fired tankless water heater because there is no need to initiate combustion.

8. The potential for Legionella growth is reduced since very little domestic hot water is “stored” in this assembly.

9. In the case of a solar thermal system, the storage tank is not heated by the auxiliary domestic water heat source. This improves collector efficiency relative to systems where the upper portion of the storage tank is maintained at an elevated temperature by an electric element or other heat source."

hot_rod

I'd like to try switching on the module with the pump sensors. I think you would have some additional delay, maybe a few seconds. Also I think the setting would need to be more like 70°F, instead the 90° Hatt mentioned. You would want to kick on even with an 80° tank, I think?

I tried several Sika switches before I had good result. They cannot directly switch the circ pump, it needs to go through a relay. I believe they have low lead versions now.

I like the Harwill switch also. It is in a PVC tee, but it seems to trip at lower flow and can switch the 120V pump directly.

I have one of each on my shop to compare performance, hence the SharkBite fitting

billyboy

If U like to build circuits, this would work.
Relay could be a Crydom D1202 etc. to drive the pump.
Thermistor 10K NTC is same as Tekmar etc. use.

billyboy

Sorry I clipped the top, it's +9 -> +24VDC