Best choice out of 2 Pumps

[dinkytoy]

I’ve got a 6 bedroom house with 4 bathrooms. There are 24 radiators in total. It’s a sealed system with an expansion vessel.

I’m going to upgrade the existing Grundfos pump to a small commercial type. I’ve already got two pumps in my possession to choose from. The Grundfos UPS2 25-80 and the Grundfos Alpha2 25-80. I’m looking for opinions on which pump to use or in fact if you think that neither of them are a good choice.

 

[ShaunCorbs]

Ups2 25-80 haven’t had any problems with them but depending on controls you might need a relay (due to amp draw)

 

[SimonG]

For a system that size I would have wanted at least 2 zones and a pump on each zone.

 

[dinkytoy]

For a system that size I would have wanted at least 2 zones and a pump on each zone.

I think that may be a future option if the pump replacement doesn’t work out. One of my problems is finding a competent heating engineer in my area.

 

[Mastermixlee]

I think that may be a future option if the pump replacement doesn’t work out. One of my problems is finding a competent heating engineer in my area.

I'm sure if you share what area you are from (only thereabouts, don't need to share entire address of course) then there may be a member on here that can help.

 

[EvilDrPorkChop]

I'd say the UPS2 too, not had any issues with them.

 

[SimonG]

I'd say the UPS2 too, not had any issues with them.

Thought they'd binned the ups2 for the ups3?

 

[EvilDrPorkChop]

Thought they'd binned the ups2 for the ups3?

Are you not thinking in the normal 15-60 range? We’re on about the 25-80

 

[doitmyself]

According to Grundfos Product Centre the UPS2 15-50/60 has been replaced by the UPS3 15-50/65. The UPS2 25-80 and UPS2 32-80 are still available.
[automerge]1574855265[/automerge]

I’ve got a 6 bedroom house with 4 bathrooms. There are 24 radiators in total. It’s a sealed system with an expansion vessel.

I’m going to upgrade the existing Grundfos pump to a small commercial type.

Why?

 

[dinkytoy]

I'm sure if you share what area you are from (only thereabouts, don't need to share entire address of course) then there may be a member on here that can help.

I’m in Reading, Berkshire
[automerge]1574879190[/automerge]

According to Grundfos Product Centre the UPS2 15-50/60 has been replaced by the UPS3 15-50/65. The UPS2 25-80 and UPS2 32-80 are still available.
[automerge]1574855265[/automerge]

Why?

The manufacturer’s installation instructions for my boiler suggest using a small commercial pump. British Gas engineer told me that using a standard pump can lead to premature failure of the heat exchanger.

 

[doitmyself]

The manufacturer’s installation instructions for my boiler suggest using a small commercial pump. British Gas engineer told me that using a standard pump can lead to premature failure of the heat exchanger.

It would help if you told us which boiler you have.

 

[dinkytoy]

It would help if you told us which boiler you have.

It’s a Potterton Suprima 120L

 

[doitmyself]

It’s a Potterton Suprima 120L

That's very useful.

The Suprima 120L is a 35kW boiler so the required flow rate at an 11C temperature drop is approx 46 litres/min or 2.76 cu.m/hr; the pressure drop across the boiler is 1.2m.

Looking at the pump curve for the Alpha2, the pump can only produce 3.2m head at 2.76 cu.m/hr, on speed 3. So this leaves only 2m for the heating circuit (3.2 - 1.2), which willl not be sufficient.

The UPS2 25/80, on the other hand, can produce between 5m and 8m head at 2.76 m.cu/hr, depending on speed, leaving between 3.8m and 6.8m for the heating circuit. which should be adequate.

 

[dinkytoy]

That's very useful.

The Suprima 120L is a 35kW boiler so the required flow rate at an 11C temperature drop is approx 46 litres/min or 2.76 cu.m/hr; the pressure drop across the boiler is 1.2m.

Looking at the pump curve for the Alpha2, the pump can only produce 3.2m head at 2.76 cu.m/hr, on speed 3. So this leaves only 2m for the heating circuit (3.2 - 1.2), which willl not be sufficient.

The UPS2 25/80, on the other hand, can produce between 5m and 8m head at 2.76 m.cu/hr, depending on speed, leaving between 3.8m and 6.8m for the heating circuit. which should be adequate.

Thanks for your detailed response.

 

[dinkytoy]

That's very useful.

The Suprima 120L is a 35kW boiler so the required flow rate at an 11C temperature drop is approx 46 litres/min or 2.76 cu.m/hr; the pressure drop across the boiler is 1.2m.

Looking at the pump curve for the Alpha2, the pump can only produce 3.2m head at 2.76 cu.m/hr, on speed 3. So this leaves only 2m for the heating circuit (3.2 - 1.2), which willl not be sufficient.

The UPS2 25/80, on the other hand, can produce between 5m and 8m head at 2.76 m.cu/hr, depending on speed, leaving between 3.8m and 6.8m for the heating circuit. which should be adequate.

Out of curiosity, how did you determine the flow rate was 46 litres/min?

 

[doitmyself]

From the installation manual (actually shows 45.82); but it's easy to calculate.

litres/min = (60 x kW output) /(4.18 x ΔT) where 4.18 is Joules Constant, and ΔT is the difference between flow and return temperatures.

I should have said 46 litres/min assumes the boiler is set to "Winter". If it's set to "Summer" the flow is approx 31 litres/min.

 

[dinkytoy]

From the installation manual (actually shows 45.82); but it's easy to calculate.

litres/min = (60 x kW output) /(4.18 x ΔT) where 4.18 is Joules Constant, and ΔT is the difference between flow and return temperatures.

I should have said 46 litres/min assumes the boiler is set to "Winter". If it's set to "Summer" the flow is approx 31 litres/min.

Thanks again for your informative response.