Arthur Sanctuary House

Arthur Sanctuary House

A2 Dominion Housing Group

case study - client logo

Project Brief - To undertake a refurbishment of heating plant to improve efficiency and reliability of equipment. Resolve issues with incorrect previous installation by others.To undertake a refurbishment of heating plant to improve efficiency and reliability of equipment. Resolve issues with incorrect previous installation by others

The Existing System

The existing heating plant originally consisted of 4 No. 200Kw standard efficiency boilers with a primary twin pump set providing heat to a low loss header; heating within the building was supplied via a twin pump unit from the low loss header to individual radiators throughout the building, each radiator is controlled by a thermostatic valve to give local temperature control. The system was weather compensated by a Drayton DC1100 compensator controlling a variable temperature valve and actuator on the heating flow.

Hot water was generated indirectly via a twinset primary pump from the low loss header to a 350Kw plate heat exchanger with hydraulic thermostatic by-pass valve to control secondary water temperature. Hot water was stored in a 750 litre buffer vessel and circulated by two secondary circulators to distribute the heated water throughout the building.

Existing System Issues

The existing system was proving to be very unreliable and several issues were raised by the client, following several visits to site we carried out a survey on the entire plant-room installation and found several key points that required remedial works, the key points were as follows, two of the existing boilers had been partially dismantled to provide emergency spares for the remaining two boilers, this resulted in the boiler output being halved causing issues when ambient temperatures dropped and increasing demand on the existing boilers, the flow and return pipe-work was incorrectly sized limiting boiler output available, these boilers were in excess of 15 years old and some parts were becoming difficult to obtain, the low loss header was found to be undersized and causing issues where the heating pumps were depriving the hot primary pumps when in operation.

The existing heating pumps were three speed units and following and calculations carried out proved them to be of insufficient size and output for the system.

The hot water pumps were found to be vastly oversized for the system and causing the hydraulic valve to fail due to excessive pressure on the seating of the valve (this valve had been replaced several times within the last few years).

The hot water buffer vessel was tested under normal use and found to undersized, the vessel was found to be completely depleted of stored hot water within 6 minutes of isolating the primary heating supply.

The system was found to have an excessive amount of suspended solids, sludge and scale causing the strainers to block frequently and the radiator thermostatic valves to fail on a regular basis; this was also causing the boilers to kettle and overheat due to the reduced diameter of the waterways.

Proposed Solutions

Following a meeting with the client we proposed that a three stage refurbishment be carried out to minimise the disruption to the staff and residents and ensure reliability of the system.

Stage 1 - To supply and install a new set of inverter driven variable speed heating pumps, this allowed the flows rates to be accurately adjusted at each stage of the refurbishment to give optimum performance within the system.

Stage 2 - To supply and install a new low loss header and install a ‘Magnaclean’ unit. The low loss header was installed to give correct flow rates to the hot water and heating system when both in use and decrease water velocity within the header, a ‘Magnaclean’ unit was installed to remove debris

Project Challenges

To ensure continuous supply of hot water and heating to the residents and social club.

To ensure minimal disruption to the employees, residents and social club members whilst work was being carried out.

Provide a reliable efficient system.

Install a clean and user friendly plant room that would ensure safe egress/ingress for anyone requiring access to the plant.

Project Details

Stage 1 - Was carried out without disruption to the tenants or social club, the heating system was then balanced to ensure that the entire system was giving the required output and all rooms and they were achieving their required temperature set points throughout the winter period, this was carried out within one day and the system was off line for a period of 3 hours.

Stage 2 - A new low loss header was prefabricated by our own in house welder prior to attending site, all materials were delivered to site and with careful liaison with the site staff a date and time was agreed to carry out the works that would reduce disruption due to low ambient temperatures and hot water demands. Notices were displayed informing residents of the intended times that the installation would be carried out. The low loss header and ‘Magnaclean unit were installed within one day and the system was offline for a period of 7 hours

During the operation only one complaint of no hot water was received from all the 120 residents, staff and Social club Members. Upon completion of this work the heating pumps were again commissioned to allow for the increased volume of the low loss header and a regime was set in place for the strainer and ‘Magnaclean’ unit to be flushed on a weekly basis to remove as much debris as possible before stage 3 is commenced.

Stage 3 - Prior to removing the existing boilers temporary boilers were installed within the hot water plant room and connected to the existing system to provide uninterrupted heating and hot water to the building, the existing boilers and flue were then removed and disposed of off-site, 6 No. New Buderus GB162 gas fired condensing boilers were then installed on a frame with common flow and return connections to a low loss header ready for connection to the system, a new flue header was installed complete with a stainless steel sectional flue within the existing brick chimney terminating at high level above the chimney, whilst this was being carried out our electrical/controls engineer removed the existing Drayton compensator and installed two Buderus controllers onto the existing panel, one to compensate/optimise and time control the system and one to control the hot water and modulate the six boilers to give maximum efficiency. Once completed we liaised with the client and arranged the for changeover from the temporary boilers to the new boilers to be complete, this was carried out within 4 hrs.

Once the new boilers and controls had been commissioned and the heating fully tested four new 800L unvented hot water storage vessels were installed in the adjacent plant-room.