Setting Up Auotamtic Bypass Valve and Pump Curves

[heating12numpty12]

I wondered if someone could help me in understanding central heating pump curves? I am trying to make sure that an automatic bypass valve has been correctly set.

The boiler manufacturer requires a minimum flow rate of 1200 lit per hour.

Below is the manufactures spec for the pump:
http://productfinder.wilo.com/en/COM/product/0000002e00037bbd0001003a/fc_product_datasheet

Below is the manufacturers page for the Automatic Bypass Valve with the product installation instructions to the right of the page (downloads):

http://www.honeywelluk.com/products/...-Valves/DU144/

I am struggling in understanding how I follow the setting procedure on the second page of the Bypass Valve and the use of pump flow curves.

The pump is currently at 43 Watts and 6.3 head (according to the pump display) if that helps. Also the pump is in mode (Pump curves Δp-v (variable).

I also have the valve set to 0.35 at the moment, which I know is passing water on bypass (can hear the water noise).

I have read some of the other posts on this forum about turning the valve till you feel the pipe warming up, but that didn't work for me.

Thank you if you are able to help.

 

[Agile]

A smart pump and an auto bypass valve are effectually mutually operationally incompatible!

Since you don't really need an auto bypass valve with a smart pump then you should set it so that it just opens if all but one of your TRVs are closed.

Tony

 

[heating12numpty12]

I should have added. I have 2 diverter valves fitted, heating and hot water, so the Bypass Valve is required for when both of these are closed.

No TVR's on the system.

 

[Richardthe3rd]

A smart pump and an auto bypass valve are effectually mutually operationally incompatible!

Since you don't really need an auto bypass valve with a smart pump then you should set it so that it just opens if all but one of your TRVs are closed.

Tony

Correct Tony.

 

[D_Hailsham]

The boiler manufacturer requires a minimum flow rate of 1200 lit per hour.

You have either a 14kW or 28kW boiler. Which is it?

The pump is currently at 43 Watts and 6.3 head (according to the pump display) if that helps. Also the pump is in mode (Pump curves Δp-v (variable).

6.3m head is very high. It's almost at the pump's limit. Do you know what the boiler's flow and return temperatures are?

Boiler make and model would also help.

 

[heating12numpty12]

Hi

It's a 28kw boiler (Vaillant ecoTec plus 428) and I am only achieving a differential of 10 C across the flow and return of the boiler (this is when everything is warmed up). Using a digital probe to measure temperature.

I only just now reduced the pump to 5 meter head, but it made little difference to the differential.

In case it helps there are 17 radiators on the system.

Thanks

 

[Agile]

So your boiler is seriously oversized then!

The whole house calculated heat loss is unlikely to be more than 18 kW and you have a 28 kW boiler!

But what is the actual output power set to in the d0 parameter?

Tony

 

[heating12numpty12]

Tony

D0 is set 30. What does this mean?

 

[D_Hailsham]

It's a 28kw boiler (Vaillant ecoTec plus 428) and I am only achieving a differential of 10C across the flow and return of the boiler

No wonder you have a 6.3m head! The boiler is designed to run with a 20°C differential. The differential is inversely proportional to the flow rate. So, if you can only achieve a 10°C differential, the flow rate is twice what it should be. The resistance of the heat exchanger will be approximately four times that when the differential is 20°C, which explains the 6.3m head. Try running the pump at a lower speed setting.

Parameters d.40 and d.41 are the actual flow and return temperatures.

In case it helps there are 17 radiators on the system.

At an average of 1.5kW per rad, that about 25kW, so the boiler may not be as much oversized as Tony suggests.

The best way of finding out how big a boiler is required is to use the Baxi Whole House Boiler Size Calculator.

Then set d.0 to just above this.

 

[Agile]

Guessing 1.5 kW per rad is a very basic figure. I find that in most London properties 1.0 kW is more appropriate!

But describe your property size, style and insulation and then we can guess the most likely heat loss.

If d0 is set to 30 kW then the boiler full output is being applied. That may well be more than is required.

Reset d0 to 20 kW for the moment and see what the differentials become and how effective the heating is in this cold weather.

Water heating should be timed to start 30 min before each heating period so that the full set boiler power is available for water heating.

Tony

 

[heating12numpty12]

I just ran the boiler calculator and it came back with 26.4Kw. Also just done a radiator check and it says there is 20Kw of radiators.

Will try reducing pump speed, but I did do this today (reduced to 5m) and didn't get much of a change in differential.

 

[heating12numpty12]

The house is a 2 story, 5 bed detached built 20 years ago, suspended floor, cavity wall insulation, around 300mm loft insulation, double glazed, floor area 300sq m.

 

[D_Hailsham]

I just ran the boiler calculator and it came back with 26.4Kw. Also just done a radiator check and it says there is 20Kw of radiators.

26.4kW is high for a typical house. Is it large, old and poorly insulated?

If that's correct then you are seriously under-provided in the rad department.

Pleas post the data you used for the boiler calculator, so the result can be verified.

 

[Agile]

A 1995 house will be very well insulated and I would expect it to calculate at about 18 kW !

So set the d0 to 20 kW and see the effect of that first!

Having 20 kW of rads also supports the expectation of a heat loss in that region!

Let us know the effect of a d0=20 kW !

Tony

 

[heating12numpty12]

So I have reduced the pump speed to 5M head / 25 Watts and set D0 to 20Kw, but these settings made only few degree difference in the differential (was 54 Flow - 46 Return) now (54 Flow - 44 Return).

I changed the D0 setting whilst the boiler was running and in ramp down mode (i.e only producing the minimum amount of burn/KW), but I noticed NO change to noise of the burner. Does D0 only affect the maximum burn capacity of the boiler?

Thanks