Suitable Pump Replacement

[Berksguy]

An auto-bypass can only be used if the pump is set to a fixed speed. It is incompatible with proportional pressure as the bypass will open more as the pressure increases.

However, the flow/head curves for the UPS2 25/80 are 'flat' up to a flow of 2 to 3 m³/hr, which is equivalent to 23 to 35kW (at 10C differential) or 46 to 70 kW (at 20C diff), depending on pump speed. This means that any auto-bypass will be either open or closed all the time (depending on setting). So an auto-bypass, on its own, is effectively unusable with this pump in most domestic situations.

The way round this is to run the pump in proportional mode and have a fixed flow valve (e.g Taconova Setter) in series with the auto-bypass. The bypass will open at the required setting but the flow will be restricted by the Setter valve.

Thanks for your detailed reply. Currently the bypass in my heating system is via a towel radiator in a bathroom. Do you think it would be best to keep it this way or move to the auto bypass and setter solution?

 

[ShaunCorbs]

Thanks for your detailed reply. Currently the bypass in my heating system is via a towel radiator in a bathroom. Do you think it would be best to keep it this way or move to the auto bypass and setter solution?

depends if you go fixed speed adjustable pump then have a separate bypass fitted if you go for a load adjustable pump then no need

 

[doitmyself]

Currently the bypass in my heating system is via a towel radiator in a bathroom.

What makes you think the towel rad is a bypass?

There are only two reasons for a bypass:

1. The boiler manufacturer says it is necessary;
2. To provide a path when all motorized valves are closed and the boiler has pump overrun.

You haven't said which boiler you have or anything about your system, so I don't know which applies.

 

[Berksguy]

What makes you think the towel rad is a bypass?

There are only two reasons for a bypass:

1. The boiler manufacturer says it is necessary;
2. To provide a path when all motorized valves are closed and the boiler has pump overrun.

You haven't said which boiler you have or anything about your system, so I don't know which applies.

When the boiler was originally installed the plumber told me to never turn off the one towel radiator as it was the bypass for the boiler.

The boiler is a Potterton Suprima 120L.

Steve

 

[doitmyself]

The Suprima 120L has pump overrun. The MI's suggest either an auto bypass valve or a bathroom rad/towel rail to give the required circulation when motorized valves are closed. In either case, it has to be connected to the flow between the pump and the MV. If the towel rail solution is used there is a permanent flow through the rail, even when towels don't need to be heated. Replacing the towel rail with an auto bypass would be better; but then there's the problem of heating the towel rail. It would need connecting to either the CH or HW flow after the motorized valve(s).

I have assumed that you have two motorized valves. If you have only one mid-position valve (3 pipes connected), you don't really need a bypass as one port is always open.

The MI's also say that a large domestic/small commercial pump is required due to the high flow rate and large pressure drop through the heat exchanger. The UPS2 25-80 is not ideal, but it will work.

 

[Berksguy]

The Suprima 120L has pump overrun. The MI's suggest either an auto bypass valve or a bathroom rad/towel rail to give the required circulation when motorized valves are closed. In either case, it has to be connected to the flow between the pump and the MV. If the towel rail solution is used there is a permanent flow through the rail, even when towels don't need to be heated. Replacing the towel rail with an auto bypass would be better; but then there's the problem of heating the towel rail. It would need connecting to either the CH or HW flow after the motorized valve(s).

I have assumed that you have two motorized valves. If you have only one mid-position valve (3 pipes connected), you don't really need a bypass as one port is always open.

The MI's also say that a large domestic/small commercial pump is required due to the high flow rate and large pressure drop through the heat exchanger. The UPS2 25-80 is not ideal, but it will work.

Thanks again for your detailed responses.

There are two separate motorised valves in my system. The towel rads coming on when the hot water is being heated is usually a good thing. However, on the few summer days where we get high temperatures, it would be useful to be able to turn off the radiator.

What would you suggest as an alternative to the UPS2 25-80?

Steve

 

[doitmyself]

There are two separate motorised valves in my system. The towel rads coming on when the hot water is being heated is usually a good thing. However, on the few summer days where we get high temperatures, it would be useful to be able to turn off the radiator.

So you will need an auto bypass to take the place of the towel rad, which will need its flow moved from after the pump to after the HW valve.

What would you suggest as an alternative to the UPS2 25-80?

The 25-80 will be fine. It's just that the pump will not be working at the optimum point on its flow/head curve, so running costs will be slightly higher.

 

[Berksguy]

I arranged for a heating engineer to call around yesterday to have an initial look at the work I need undertaking. He didn't turn up and when I rang him he provided a feeble excuse for not coming. So I'm still looking for a good heating engineer that carries out work in the Reading area.