Hot Water System
Communal Centralised Hot Water Supply System
Background
The National Charity of Elizabeth Jane Jones provides housing for the poor. Established in 1934, the charity owns the Fairholme Estate in Bedfont, Middlesex, comprising a central hall and 72 houses and bungalows set in 2 acres of gardens.
The Problem
In July 1991, indirect calorifiers were replaced by two Beaumont Energymaster hot water generators to supply domestic hot water to the residences and central hall via a 50-year old underground pipeline. In 1992 the overall system efficiency began to cause concern: the HW Generators could not cope with the demand, flow temperatures had dropped dramatically and residences at the end of recirculating loop were not getting any hot water. It was found that the pipework was so scaled up that between 15 and 20 degrees Centigrade was being lost between the Flow and Return. This was known to be due to the reduction of the bore of the pipework which resulted in a low volume of hot water being moved around the system. Scale within the generators was preventing them reaching the set temperature.
The Solution
The conventional solution would have been to either replace the pipework, or acid descale it, and to chemically descale the generators. Both options are expensive and disruptive. In November 1992, two Industrial Electronic Descaling Systems were commissioned and installed by Environmental Treatment Concepts. One unit was fitted to the cold feed to the boilers (54mm pipe), the other to the return leg of the recirc pipe (28mm pipe). To track the progress of the system descaling, it was decided to monitor key temperatures, over a period of four weeks, under similar and controlled conditions. The following results were recorded and plotted in graph form:
On the day of installation the following temperatures were recorded:
- a. Flow - 45 degrees C.
- b. Return - 27 degrees C
- c. Differential - 18 degrees C
Within just one week the Return temperature had improved by over 5 degrees, due to the scale beginning to be removed from the recirculating pipework. After the second week, the HW generators began to increase in efficiency, as their scale began to dissolve away and therefore the Flow temperature started to increase sharply. The closing of the Differential temperatures indicated that scale was continually dissolving from the pipework, thereby improving circulation.Within only four weeks the system had approached its designed performance, giving the following temperatures:
- a. Flow - 62.5 degrees C, (increased by 17.5 degrees - 39%)
- b. Return - 58.4 degrees C, (increased by 27.8 degrees - 103%)
- c. Differential - 4.1 degrees C, (reduced by 15.9 degrees)
Fifteen months after installation, a representative of Beaumont (UK) Ltd. carried out an inspection of the Energymasters and found them to be clear of scale. Fuel bills to heat the hot water supply to the residences and central hall had decreased from £1,000 to £535 per month.
Pay Back
In calculating payback, the following conservative assumptions were made:
- a. In calculating annual fuel usage, it is assumed that more hot water is used during the coldest four months of the year, Dec/Jan/Feb/Mar. The Electronic Descaling Equipment was installed in November, thus covering this period.
- b. For the other 8 month period, it is assumed that the cost of supplying hot water was two thirds that of the coldest period.
- c. In calculating the fuel usage on the system left untreated, it is assumed that the scale build-up would not increase.
Fuel Cost - System left Untreated:
4 x £1000 = £4000
8 x £ 666 = £5328
Annual Fuel Cost = £9328
Fuel Cost - System Electronically DeScaled:
4 x £535 = £2140
8 x £356 = £2848
Annual Fuel Cost = £4988
Annual Savings - £4,340
The cost of the Electronic Descaling Equipment was £2,228 (54mm & 28mm pipes). The payback period therefore, in fuel savings alone, was just 6 months.
