Sizing Solar Water Heater tank

[bernard]

Hi.
I am interested in sizing solar water heating tank, and found a couple of rule of the thumb ways to calculate it:

a) 1.5 gallons (2 gallons in Sun Belt) of hot water storage for every solar panel's active area (aperture area) square foot.
b) 80 to 100 liters per person (21 to 26 gallons per person).
c) 1.5 to 2 times more than the daily hot water consumption.

I was wondering if you could comment on these, and if they are not correct advice some other method of calculating a tank size?

Thank you for the reply.

[LucMan]

20-30 gallons of hot water per day per person is the starting point, every family is different. I have seen showers with 4 huge shower heads with no restrictors.
You can calculate how much HW that you actually use by checking the specs on your dishwasher, washing machine, etc.
You can measure your shower, and faucets using a bucket.
After you perform all the measurements you may find ways to economize on your HW use by installing water saving shower heads and aerators on your faucets.
Here in NY an 80 gallon tank with 64 sq. Ft. of panels is the sweet spot for most homes with up to 4 people.

[bernard]

You can calculate how much HW that you actually use by checking the specs on your dishwasher, washing machine, etc.

Thank you LucMan.
How does the upper sum of dishwasher/washing machine hot water usage relate wit tank size? Is there some factor by which the hot water summation value should be multiplied with?

[LucMan]

Depends on where you live, and how much extra you want to spend. Larger tanks and more panels raise the cost.

[saniconenergy]

Regarding solar water heater or any other water heater tank sizing and calculation

As an expert in this field from the last 15 years , i would recommend you to go through the link given below, which is a complete solution for any of the requirement related to sizing of the water heater tank or what would be the best solution in water heaters as per location and family members.

https://saniconenergysolutions.wordpress.com/2015/08/31/having-a-home-inspection-first-is-a-smart-move-prior-your-investment-in-a-water-heater-system/

[bernard]

Thank you for the article Saniconenergy!

I apologize for not replying in time. I definitely got an email that a new reply has been added to this topic, but for some reason did not check it.
Your article is very informative, thank you for sharing it.

Would you mind If I ask one question on this part of it:

And through above calculations, i would recommend 450 Liters capacity of Solar water heater. 380 Liters is your actual demand, minus 60 Liters required for guest room, as it would not be occupied regularly which comes out to be 320 Liters. Balance 130 Liters is your cushion.

What is the basis of adding 40% to the initial demand:

320 Liters demand + 130 Liters (+ 40% of demand)

?

Thank you.

[J.P.M.]

Hi.
I am interested in sizing solar water heating tank, and found a couple of rule of the thumb ways to calculate it:

a) 1.5 gallons (2 gallons in Sun Belt) of hot water storage for every solar panel's active area (aperture area) square foot.
b) 80 to 100 liters per person (21 to 26 gallons per person).
c) 1.5 to 2 times more than the daily hot water consumption.

I was wondering if you could comment on these, and if they are not correct advice some other method of calculating a tank size?

Thank you for the reply.

All of the above, considered together, are probably good enough. Size The tank to the load, and size the collector to the load. if the gal./ft.^2 is ~ 1.5-2.0 gal./ft.^2 leave it. Otherwize, err a bit on a larger tank, but not too much. Better to get low flow shower heads and reduce the load. Also, consider steeper tilt if grossly oversurfaced in the summer.

[saniconenergy]

Thank you for the article Saniconenergy!

I apologize for not replying in time. I definitely got an email that a new reply has been added to this topic, but for some reason did not check it.
Your article is very informative, thank you for sharing it.

Would you mind If I ask one question on this part of it:



What is the basis of adding 40% to the initial demand:

320 Liters demand + 130 Liters (+ 40% of demand)

?

Thank you.

Hi
Any kind of system has a certain drawing capacity. Meaning that the moment you start withdrawing hot water from the system, the cold water starts entering into the system, thus reducing the temperature of the stored hot water gradually. Now based on our experience we have seen that if you have stored 100Liters of hot water, then after mixing of cold water, only 60Liter would be in the usable temperature range. So the balance water is heated up to counter the temperature reduction effect taking place due to an infusion of the cold water."

[J.P.M.]

Hi
Any kind of system has a certain drawing capacity. Meaning that the moment you start withdrawing hot water from the system, the cold water starts entering into the system, thus reducing the temperature of the stored hot water gradually. Now based on our experience we have seen that if you have stored 100Liters of hot water, then after mixing of cold water, only 60Liter would be in the usable temperature range. So the balance water is heated up to counter the temperature reduction effect taking place due to an infusion of the cold water."

I don't know if this qualifies as some corroboration, but, FWIW, my actual DHW use load is ~ 25,000 BTU/day. Add to that ~ 11,200 BTU/day somewhat exhaustively measured over the last 8 years for tank standby and tank ancillary piping losses, and about 3,700 BTU/day average collector piping loop losses while operating, gives an AVERAGE daily load of ~ 40,000 BTU/day of which about 38% is for thermal losses.

[bernard]

Thank you for the replies both J.P.M. and saniconenergy.

[J.P.M.]

Thank you for the replies both J.P.M. and saniconenergy.

For my part, you are welcome.