positioning of secondary circulation pump

[Dr Doolittle]

Very last rad on heating circuit is a vertical mounted iguana circo rad, which is 1.8m high. The rad is not getting sufficient water flow even after balancing all other rads. Placement of a secondary circulation pump will alleviate this issue but the question is where best to locate it. Near the rad or anywhere for convenience of fitting?

 

[SJB060685]

CCT's at the boiler and a separate system pump. Pumps in series not a good idea.

 

[Dr Doolittle]

CCT's at the boiler and a separate system pump. Pumps in series not a good idea.

so disable the combi pump and bring the flow/return pipes closer together on the combi? How close is close? How do you disable the pump for CH but make it work for DHW?

 

[SJB060685]

No you wouldn't be disabling the boiler pump, that will still circulate through its primary loop. The CCT's are hydronically separating the primary loop from secondary and thus allowing the pumps to run without interfering with each other. You'll find lots of conflicting views on CCT distances etc. Some say a maximum centre distance of the tees as four times pipe diameter and others argue and prove thats not the case, I have seen them further apart. If the boiler primaries are in 22mm then go up a size to 28mm, this further reduces the pressure loss across the tee's, which is affectively whats desired, you want a nice minimal resistance and low pressure drop, if the resistanceis too high you're affectively back to two pumps in series. When the additional system pump is energised through demand along with the boiler the additional pump will draw its flow rates, while the boiler pump circulates its own through the primary loop.
Google CCT's, Caleffi display a lot of information in images so you can visualise what I mean. There are other ways to hydronically separate and better but tee's is a lot cheaper and serves the purpose.

 

[Dr Doolittle]

so I would have to create a secondary loop for each radiator which in turn would have tertiary circuit for flow/return from the valves? How many of these secondary circuits do you need? One for each radiator or floor or zone? How do you connect the primary to the secondary
I have a 3 port manifold on the 22mm flow pipe which in turn feeds 3 radiators. Are these 3 secondary circuits or are they CCT's a centimeter apart?

 

[SJB060685]

Something like this is what I'm suggesting. You would then have hydronic separation between boiler circuit and secondary circuit.

 

[Dr Doolittle]

so I have a flow from the boiler, through the house and then back again as a loop (primary?) I would then join the flow/return together and have a CCT on the 22mm pipework so joining the circuit together and then back to the boiler? That's easy enough to put in. How near the boiler should they join/separate as primary/secondary? The boiler has a variable speed pump but the additional pump will not be able to be controlled in the same way (slow down/speed up the flow in unison). the new pump need to be on the flow of the secondary circuit right!

 

[ShaunCorbs]

Eg for a two zone set up

pump is on the flow

 

[SJB060685]

Image taken from a friend of mine but I hope it shows you what I'm saying. You can create this hydronic separation at the boiler, or as far as you want.
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Eg for a two zone set up

pump is on the flow

View attachment 46516

Wonder where you stole that from

 

[Brambles]

Dr Doolittle,

I have had issues with Iguana radiators not being properly installed.

Whilst they are not that large thermally, they need a 15mm connection straight from a 22mm circuit. I think that the manufacturer specifies 16mm to 18mm to the radiator.

In the case I had, two had been mounted back to back though a dividing wall and connected to a shared 15mm spur. At best they were luke warm. Once repiped each on a single offtake from 22mm one was excellent, the other marginally better. So we then read the manufacture’s instructions:

The valve mechanism is reversible for flow. However, the settings on the adjustment screws are different for left and right hand flow. One of the valves was incorrectly set. Once corrected the second rad was excellent too.

 

[Dr Doolittle]

Dr Doolittle,

I have had issues with Iguana radiators not being properly installed.

Whilst they are not that large thermally, they need a 15mm connection straight from a 22mm circuit. I think that the manufacturer specifies 16mm to 18mm to the radiator.

In the case I had, two had been mounted back to back though a dividing wall and connected to a shared 15mm spur. At best they were luke warm. Once repiped each on a single offtake from 22mm one was excellent, the other marginally better. So we then read the manufacture’s instructions:

The valve mechanism is reversible for flow. However, the settings on the adjustment screws are different for left and right hand flow. One of the valves was incorrectly set. Once corrected the second rad was excellent too.

they already have that size fitting as the first thing I did was speak with support to verify the install.
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I should also add that I'm running the heating flow @ around 35-45 cent so I keep it switched on like a UFH system. I think this cool flow is the problem and when I switch to thermostat control the big rad heats just fine. So with low temp flow I need a greater volume to achieve output. That was probably information that should have been stated at the beginning actually.

 

[Brambles]

I don’t think that converting to a hydraulically separated system will make any discernible difference to the performance of your Iguana radiator. You are probably already at or close to the optimum flow rate of your installation. The solution lies elsewhere.