Central Heating with Solar water heating (Primary) and LPG Gas Boiler combined

Old 05-01-18, 04:27 AM
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Central Heating with Solar water heating (Primary) and LPG Gas Boiler combined

Help Needed to Combine Solar water heating system (as primary source) and LPG Gas Boiler (as a secondary source) for Central Heating. I have no experience on Central Heating before. But I am a serious DIYer.
I am from Kathmandu, Nepal, and presently trying to install a central heating system in my house using Solar Water Heater.
Background: Winter days in Kathmandu lasts about 130 days a year. Minimum temperature during the night is Zero degrees Celcius and During the Day time is 18 degrees (C). Out of 130 winter days, 120 days are sunny days (6 to 7 hours every day). Solar hot water heating systems for Domestic Hot water are very popular and have been in use already more than 2 decades successfully. I am going to use the similar system to heat the water and store in a storage tank and circulate it through radiators through out the winter. This new system will be used solely for heating purpose and NOT for Domestic Hot Water.
After careful calculation of Heat requirements and Radiator planning for every room, I have decided to have a 1000 liter hot water storage tank and 5 solar panels to heat the water on my roof top (have ample of space on my roof for this). Water temperature is easily heated to 70-80 degrees (C) solely by solar panels. This water will circulate in the radiators and back to storage tank. In my approximate calculation the 1000 liter tank will keep my house warm till 3 am in the morning, and then the water temperature will go down, as there is no sun during the night and also during cloudy days. From that point, I wanted to install a LPG Gas Boiler to heat the water.
I got into few confusion on where to install the Boiler:
Option 1. Shall I install it bypassing the storage tank thus boiler needs to heat only the volume circulation in the radiators and not the whole 1000 liter tank?
Option 2. Shall I install it to heat the water inside the storage tank and heat the whole water?
Option 3. Water from Storage tank flows through Boiler then to Radiators. Boiler is controlled by Room Thermostat. But not sure if the water can still flow when Boiler is not running. (Diagram Attached)

I have 2 thermostats in the room as a reference of temperature.
One thermostat to stop the Circulating pump if Room Temperature is more than 24 degrees (C).
2nd Thermostat is to start Gas Boiler if the Room Temperature falls below 16 degrees (C).

The problem I am facing if I choose Option 1: the Boiler will start when temperature drops below 16 degrees. Then I do not need to run the Circulating Pump - how to turn it off. And vise versa? I am attaching a diagram for the reference on what I am planning to do. Any help and if anyone had an experience with similar installation would be a really great help. Presently during winter days - we are using Fireplace in the Sitting Room and everyone gathers around it in the evening, while remaining house is cold with as less as 9 degrees (C). Thank you all in advance.

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Old 05-01-18, 10:51 AM
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How about this?

Boiler hot water output with its own circulator and check valve tees into the hot line from the solar tank after the solar loop circulator and check valve and before the branches/manifold for the radiators. Return from radiators has tee out to boiler after the manifold or convergence of the various radiator branches and before return to solar tank. Either the solar lines have to come down to the basement or the boiler lines have to go up to the roof to reach the tees.

Sensor (aquastat) in the solar tank switches to solar circulator when solar tank contents temperature is high enough and switches to boiler circulator when solar tank contents temperature gets too low.

Room thermostat acts as master control to turn off both the solar loop circulator and the boiler circulator when room temperature is high enough..

Aquastat in boiler shuts off burner when boiler contents temperature gets high enough (probably supplied with the boiler).

Optional: Have additional individual circulators and room thermostats to have different heating zones in the house. There needs to be a master control contactor (relay) so if any of the room thermostats are calling for heat, then the portion of the system containing the solar loop circulator and boiler circulator is live.

Optional: For energy conservation an additional sensor (thermostat) for outdoor temperature is added to the master control circuit to cut power to all circulators regardless of calls for heat if the outdoor temperature is high enough.

The boiler itself can stay live at all times controlled by its own aquastat (unless manually turned off for the summer).
Old 05-02-18, 07:50 AM
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Thank you so much for the tips. Let me digest it for couple of days as the info you have provided is new to me and might be the right solution. Will work on it and get back with diagrams for your expert opinion. Thank you once again for taking time to read and reply. Warm regards.
Old 05-03-18, 04:40 AM
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After some research on your suggestion I have made changes to the diagram and have attached.
On your comments: "Either the solar lines have to come down to the basement or the boiler lines have to go up to the roof to reach the tees." - I believe I can have both the Boiler and Solar Tank on the Roof right?
Just to reconfirm on the function on Aquastat (I have never seen them before) so slightly confused:
So the sensor inside the Solar tank (Aquastat) can be adjusted e.g. if water temperature gets more than 50 degrees (C) will turn on the Solar Loop, but will turn off the Boiler and if Water Temperature gets below 50 degrees will turn on the Gas boiler, but also shut off the Solar circulation pump. Did I get you right?
Or Sensor in the tank will only turn on and off the Solar Loop Circulator and separate sensor from the Boiler shall turn on and off the Boiler?
Or Sensor from the Solar Tank turns on and off the Solar Loop and also controls the Circulator of Boiler. And separate sensor of Boiler only controls when to fire up the Gas?
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In new diagram I have added Tees as suggested (circles) and check valves (squares).

Thank you once again.

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