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Member questions: pump energy, air balancing and de-stratification pumpsFebruary 2018

Steve Sansom, Information & Knowledge Manager, BSRIA
Compiled by Steve Samson, Information & Knowledge Manager, BSRIA

Q. I’m involved with a project where the main task is to reduce pump energy consumption. The system is a LTHW heating system with two No. pumped secondary circuits; a constant volume circuit with three port control valves at AHU coils and a pumped radiator circuit with TRVs.

I intend to change three port control valves to PICV and add DPCVs to the radiator circuit branches.

As per the BSRIA guidance, I’d like to locate the pump pressure sensors at the extremities of the circuit, using a number of sensors in case the index moves. However, I just need to understand the interaction between the DPCVs and pressure sensors as it seems both are trying to achieve the same thing. My question being if the DPCVs are maintaining constant pressure in the system and at the terminals, will the pressure sensors see much of a variance in the system pressure and hence not ramp the pump speed down?

After researching this, it does specify the location of the sensors to be across the most remote DPCV. This keeps a constant pressure between A and B and avoids any fluctuations so will limit the possibility for the inverters to constantly ramp up and down. The information is contained in BSRIA Guide BG 12/2011 Energy Efficient Pumping Systems.

Just to be on the safe side, we advise confirming this with a design consultant. It is also important to identify the cause of each failure in enough detail to ensure that time and effort are not wasted trying to treat symptoms instead of causes. On the other hand, it is equally important to ensure that time is not wasted on the analysis itself by going into too much detail.

Q. I have a query over Balometers and the use of them as a balancing tool, meriting correction to allow for back pressure on flow. We are disagreeing on the measured flow rates and need clarification.

The BSRIA Publication Commissioning Air Systems (free to members) answers this question. The relevant sections are 5.4 (pg. 33) and 6.3 (pg. 45).

Q. Please can you advise me on an issue we have with regards to de-stratification pumps fitted to hot water calorifiers. We currently do not fit de-stratification pumps to our domestic sized cylinders due to the amount of constant turnover of water, but we do fit them on our commercial sized calorifiers. Can you advise if there is any measurements based on volume, usage or outlets that defines what is considered domestic and commercial. Or, if there is any measurements based on volume, usage or outlets that defines when a de-stratification pump is required?

The consideration of domestic versus commercial is usually driven by the utilisation of the building, and the corresponding design requirements and regulations it will have to meet.

Fitting a domestic or commercial hot water calorifier in the building is the result of the above considerations.

Now the manufacturers tend to categorise domestic and commercial calorifier per volume and power output (kW heating capacity) as usually smaller volume and power is required in domestic than in commercial buildings.

Regarding de-stratification pump consideration, you may look at BS 6700:2006 Annex C Guidance on the calculation of hot water storage capacity to find further explanations from a design point of view.

Q. I have seen that the Soft Landings Framework is going to be updated by the end of the year. Any news on this?

An updated of the Soft Landings Framework is going to be produced and will be published in 2018. In the meantime please see the range of free to download BSRIA Soft Landings Guidance including the current Framework.

The publications mentioned in the questions above are all available for members to borrow from the BSRIA library, open 8.30 - 5.00 pm Monday to Thursday and 8.30 - 4.30 pm on Fridays.
E: information@bsria.co.uk T: +44(0)1344 465 571

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