Entries Tagged 'Radiant Heating' ↓

Okay, now that the primary loop is established, there are a few exceptions to go over.

1. I show most of my zoning of secondary circuits as zoning with valves, but you can also zone with pumps which can be a great way to do it, but pumps are expensive and this is usually only cost effective if you are doing fewer but larger zones.
2. The water fill usually occurs at the air-compression tank, but on my last drawing I showed it as filling at the return side. This is usually seen on older boilers, on new installs or modulating boilers it is best done at the tank.
3. On this post, I am showing the concept behind secondary circuits, not the exact science. So don’t run off and install per this drawing as the balance will be off!

The primary circuit just cycles hot water like a rotary circles cars in traffic. The secondary circuits are like the side streets that draw as the demand requires. With this setup, you can mix higher temp radiators in a system with lower temp hydronic floors and not starve the one or overheat the other…

Basically you are zoning the different types from one another.

This is how the secondary loops connect to the primary

If you feel lost or overwhelmed, this should help. If your house is old and has an original radiator-heat boiler system, then the radiators are probably the primary circuit. The pipe leaves the boiler and goes on a loop with each radiator having a branch supply and branch return. It is unlikely that the system has any connections between supply and return that are not a radiator of some sort. This was a simple way to pipe the system and required only one pump (albeit a relatively big one) to circulate the water.

The bummer of it is that room-by-room temp control is more difficult and is a bit of a fumbling science. Also, air problems are shared by every component in the system. And if all that was not enough, one thermostat controls the whole thing! Simple, but not very accurate and a waste of energy.

After the main hydronic loop is completed, we get into the circuits. On a standard and simple hybrid system, we have two circuits. The first is the radiator circuit which supplies and returns hot water to and from the cast-iron radiators. Two trunk (supply and return pipes that have branches to each radiator) lines carry the water and the radiators have valves on the supply side of each to manually control the volume of water passing through the radiator thus raising and lowering the temps of each radiator. The radiator circuit is a “closed circuit” technically  as there are no lines connecting the supply and return lines in the circuit, all water must pass through a radiator if it is to go from the supply to the return.

The second circuit is the radiant heating circuit. I will address this in the next post as I will need to include a drawing to explain this (don’t take this personally, I needed one too and still do sometimes).

Now that we have established the boiler and main hydronic loop, lets go over what makes up that loop. The hydronic loop is used on open-system type hydronic heating layouts. There are two water pipes attached to the boiler. The first is the hot water supply from the boiler to the radiators, the second is the return line that takes the water cooled from the radiators back to the boiler. This return line usually has a pump (boiler circulator) on it to help the water into and through the boiler. The thinking used to be that pump is best installed in this location as it is both efficient and prolongs the life of the pump as it is pumping the coolest water. Not true any more as modern pumps can handle the supply water heat, and by putting the pump on the supply side, it can go downstream of the air-pressure tank which allows the pump to have equalized psi on the inbound and outbound sides since it is not pumping into the diaphram tank which is designed to absorb pressure (like that of a pump!). Sometimes, another item on the return leg is the fill line. Again, not a good idea by modern standards. This should be connected at the air-tank and scoop location on the supply side of the boiler, but upstream from the primary system pump. This way, any cold water allowed into the system is not then dumping on the hot boiler elements which can cause damage. Instead it can blend with the hottest water and be returned to the boiler at or near the overall return temp. This line is connected to a fresh water supply to allow the system new water for filling the system and maintaining pressure. When installing this line, one should use a backflow preventing device to prevent water from the heating system from flowing back into the domestic water supply. Then we have the hot supply line. On this line there are not usually any items installed before the loop as the heat and flow of the water should be left as unaltered as possible. Then we have the loop itself. The loop is a connection of the two pipes from the boiler, isolating valves, an air purging valve, an expansion or pressure balancing tank, another circulating pump after the air vent that pumps in the direction of the supply, water supply sensors (if the boiler supports these), and usually a set of temp and pressure gauges. Most hydronic heating systems in homes do not operate a pressure of more than 25-27 psi. The final part of the loop is a set of supply and return pipes going to the zones that then completes the loop.

And if you have more than one secondary loop, then there will be a pipe to connect the supply and return sides of the primary loop to send unnecessary heated water back to the boiler. In other words, if you have three secondary circuits and only one is calling for heat, the capacity produced by the boiler that is not needed can then go back to the boiler as higher temp return water which lowers the amount the boiler needs to heat the water it is sending (this really only works to any noticable degree on modulating boilers).