Electric hot water source for radiant floors and domestic hot water

orange_cat · October 2023

GroundUp said:
There is almost zero chance that you need anywhere near 20kw for domestic water, when you have some storage. This does not need to be so complex. What Thermo 2000 told you was either misinterpreted, or the person you talked to doesn't understand their product.

Are you referrring to ComboMax? Or to Thermo boiler with Indirect?
Or are you referring to ComboMax PLUS indirect?

orange_cat · October 2023

Hot_water_fan said:
Combomax delivery beyond 10 minutes is an issue - according to Thermo2000.
20kw is 20kw. The recovery is the exact same whether the tank is integrated or separate. I also think the recovery rate isn’t a concern here- you’d have a almost 200 gallons first hour rating. That’s plenty!

First hour ratings are not great when I have 3 concurrent showers. The fact that SOME water is recovered between minutes 45 and 60 of the first our, does not mean that the first 30 minutes have sufficient water for 3 concurrent showers/plus dishwasher/plus laundry.

Hot_water_fan · October 2023

First hour ratings are not great when I have 3 concurrent showers. The fact that SOME water is recovered between minutes 45 and 60 of the first our, does not mean that the first 30 minutes have sufficient water for 3 concurrent showers/plus dishwasher/plus laundry.

This is well within the capacity of a 20kw boiler and a tank of 100+ gallons! Both the combomax and a boiler attached to a similarly sized indirect can do this. There’s no capacity difference between the two.

Here’s the math: 120 degree F water exiting the indirect gets mixed with 40 degree F in a 80/20 ratio gets you an average temp of 105F. For a 2gpm shower, only 1.6GPM is hot water. So only 72 gallons needed for 3, 15 minute showers there. That’s well within the capacity, plus you’ll have produced 26 more gallons in those 15 minutes.

That's assuming the water is stored at 120F. You can store it even higher (therefore using less hot GPM) and mix it down to safe temperatures further expanding the capacity.

I don't think you need any more than 100 gallons of storage (either Combomax or separate indirect) and a 20kw heater. If you find you do after a year, you can always add another indirect, so save the money upfront and decide later.

GroundUp · October 2023

orange_cat said:

GroundUp said:
There is almost zero chance that you need anywhere near 20kw for domestic water, when you have some storage. This does not need to be so complex. What Thermo 2000 told you was either misinterpreted, or the person you talked to doesn't understand their product.
Are you referrring to ComboMax? Or to Thermo boiler with Indirect?
Or are you referring to ComboMax PLUS indirect?

Any. ComboMax plus indirect would be just plain silly, since the ComboMax is already an indirect. You don't need 20kw for domestic water with storage, period. If you run hot showers for 2 hours straight on the coldest day of the year, then yes there may be an issue. But the reality is that 99.99% of households will never do that.

hot_rod · October 2023

The issue I see is determining how much water you want, how quickly. Then you design the system areondtbat.

If you want endless DHW at some gpm, the math is simple 500 . Flow . Delta T

Roughly speaking 50,000 will give you 1 gpm continuous. So a 120 boiler or tankless give you 2 gpm at a 70 degree rise

Do you want endless DHW, or a large dump , with a 30 minute recovery?

neilc · October 2023

Alan (California Radiant) Forbes said:
I installed a solenoid valve on the hot water line to the shower when my kids were young. Attached a timer which would turn on once water flow was detected. After 10 minutes, the timer would energize the solenoid.

you are evil

orange_cat · October 2023

3 showers, at 2.5 gallons per minute shower heads. Concurrent (school start the same). 10-15 min per shower.

Alternatively, 2 bathtubs at 40 gallons, and one shower (again concurrent).

Thermo salesman said not combomax and interestingly - and not intuitive to me at all - that going from 50 to 70 to 109 gallon on Combomax would make no difference for the concurrent flow. But that their standard boiler - connected ot indirect - would be fine.

Hot_water_fan · October 2023

Both scenarios are easily covered by either option.

hot_rod · October 2023

3 showers running at 7.5 gpm? Now you do mix some cold with the hot, so the load is not 6.5 on the hot only. Typically you run the hot water to the building not above 120, mix down to 103- q105 maybe for a shower.

As far as tank, you can p,any with the storage temperature, add a mix valve
A 40 gallon tank at 150, mixed to 120, gives you over 60 gallons of useable water temperature.

Lochinvar has a calculator for that at their site. Reverse Indirects need fairly hot tank temperature to give you full performance. You may need the tank at 180 to get decent performance. The Turbomax output charts tell the story

Larry Weingarten · October 2023

Hi, To follow on @hot_rod 's comments, the usual mix is 70% hot and 30% cold water. You could measure temps and be more accurate. Also, 1.5 gpm showerheads can give a very nice shower. Why not use those? Together these measures would reduce the load down to 3.15 gpm of hot water for three showers.

Yours, Larry

orange_cat · October 16

Me again! Thermo200 sales people suggest the following:

1 Indirect (Ours would be the turbomax 50-5)

1 60 or 80 gallon domestic storage tank (source by others as we do not manufacture them)

1 20 kw electric boiler BTH Ultra 20kw

1 Taco SR Circulator Zone controller

1 Brass circulator (recirc domestic between the indirect and storage tank)

How does this look to you all?

And what I do not understand is

(1) what heats the floors (just straight on boiler, not tank at all?)

(2) is there any advantage of using 4,500KWH DHW at 85-100G capacity instead of pure storage tank and if so, how would the indirect and this one work together for the DHW needs? For reasons unclear to me the local people suggest this.

Jamie Hall · October 16

https://forum.heatinghelp.com/discussion/comment/1767304#Comment_1767304

Good man. I'm right with you. I'd want a recovery rate of a at least 180 gallons per hour.

DCContrarian · October 16

https://forum.heatinghelp.com/discussion/comment/1814638#Comment_1814638

You don't need to run at 3 gpm all day, just for 15 minutes or so in the morning. A first-hour rate of 80 gallons or so should do it. A biggish tank and you've got all day to fill it.

I'd also look more aggressively at low flow showerheads. I installed the High Sierra 1.25 GPM heads in every shower in my house. They're really nice and use a lot less water, we get five showers out of a 65 gallon tank with no complaints.

hot_rod · October 17

the Turbomax is what makes the hot water, the second tank is just giving you additional dump capacity.

Turbomax has a nice sizing software program to give you all the correct tank sizing. if you give them actual, accurate dhw load data, then the system they sized should work fine.

if the same boiler has heating circuits, typically those are shut off while the full boiler output recovers the dhw tanks.

If you want to be able to heat and generate DHW at the same time, then the boiler needs to be sized to cover both loads. That info also goes into Pierre's software calculation inputs.

So it's important that you put the correct data into the calculations.

An as everyone has mentioned, consider lower flow shower heads, then all the equipment can size down. As well as operating costs.

The brass recirc pump just mixes the water from the Turbomax to the extra storage tank

orange_cat · October 17

We downgraded all shower heads to 2GPM but that is still 6GPM concurrent - but thank you for the suggestions.

Electric hot water source for radiant floors and domestic hot water

Comments

Categories