Heat exchanger Question

Magicare

I'm new here but wish I had found this site long ago.



I have designed and built an in floor hydronic heating system for a new



home I'm building in Ontario cottage country.



Because we are located where natural gas is not available one of the aims



of the new system is to take advantage of low rate electricity offered by



the Smart Meter System soon to launched in Ontario.



I am using a Monitron EH25 electric boiler to heat a 1000 gallon tank of



water which will be my energy reservoir. The boiler, through a closed



circuit with a heat exchanger, heats the tank of water up to 180F at night



when the power costs about 5.2c/ kWh. For a heat exchanger I'm using a



modified automotive radiator situated in the bottom of the tank.



This much is completed and works just fine.



The heat loss calculation for the house indicates that the maximum heat



loss to be around 60,000 BTU/hr.



I have built most of the 2 manifold distribution system with 4 zones of



250 feet on each mainfold but am still trying to figure out how large a



heat exchanger I will need for the heat distribution side of the system,



this will also be a modified automotive radiator.



Anyone have a calculation as to how many square inches of a copper water



to water heat exchanger will be required to extract 60,000 BTU/hr and



deliver an output temperature about 20 degrees cooler than the tank



temperature?



Perhaps a little more information would help.



The 160 degree water , from the distribution heat exchanger, will be



tempered using 3 Honeywell mixing valves before being sent to circulating



pumps then to throttling manifolds for the hydronic tubing. Three mixing



valves are used because of the differing types of floors being heated,



garage, slab on grade and engineered flooring on joists. The output



temperature from the mixing valves will be adjusted to a temperature



appropriate for the type floor being heated.



The tank water will not be circulated through either the boiler or floor



tubing because I'm using cast iron pumps which  will require an inlet pressure of about 5 p.s.i. at these temperatures to prevent

cavitation. By using heat exchangers for both the boiler and distribution

circuits I'm able to prevent oxygen entering the water and will be able to

pressurize each of those circuits to establish the appropriate pressure at

the pump inlets.



The only thing I've not been able to get a handle on is the required



surface area of the distribution heat exchanger.



Thanks.