HEAT LOSS IN HOT WATER SYSTEMS CALCULATIONS

The Aquadron is a Legionella control system that protects 24 hours a day, it also saves you energy. Call us on 0333 772 0043 to find out more

WATER TEMPERATURE Vs HEAT LOSS AND COST IN HOT WATER SYSTEMS

It is hard to calculate savings due to reduced heat loss as every site is different - bigger diameter pipes lose heat quicker and the heat differential plays a big part i.e. a pipe in a room at 20 degrees – that carries liquid at 40 degrees will lose heat at half the speed of one carrying liquid at 60 degrees. There are some charts  here - http://www.engineeringtoolbox.com/heat-loss-insulated-pipes-d_1151.html

One way to look at cost reductions is to assess the amount of water circulating and the temperatures at which it circulates, lets assume the following –

(but read the information below first!)
Heat loss from hot water systems
Hot water flow (driven by pumps) occurs continually. Whilst flowing through the network the hot water loses heat energy to the environment. The temperature loss on the way through the circulation depends on the size, age and insulation of the piping system, as well as the temperature differential between the water in the pipe and the ambient air temperature around the pipework. Often the water which went into circulation with 60° C returns at 45-55°C. (60° C is the temperature value in the technical rules for thermal prophylaxis in Europe).

This loss of heat energy must be replaced to bring the water back to 60° C, or whatever temperature the boiler system is set to. The more water that circulates in the system and the higher the temperature loss is, the more energy that is necessary to bring the water temperature back to the starting temperature. If the microbiological prophylaxis is done by another measure, such as treatment with anolyte, the hot water temperature in the circulation can be reduced from ≥ 60°C to say 45-50°C. From the thermodynamics the loss of heat energy in the circulation can thus be reduced.
heat loss rate from hot water pipes
Example
If a water system circulates 4,000 litres per hour and if the boiler outflow temperature is 60°C and the return is 55°C we can easily calculate how much energy is needed to return the water to 60°C.

The calculation is as follows - flow rate (m3) x heat loss (°C) x specific heat capacity of water (1.16) 
So for our example = 4 x 5 x 1.16 = 23.2kWh per hour.

To find the cost we multiply the kWh requirements by the fuel cost and the boiler efficiency expressed as a decimal.
Assuming that gas costs £0.04p per kWh and that the boiler has a 70% efficiency -
23.2 x (£0.04/0.7) = £1.33 per hour = £31.92 per day = £11,650 per annum.

By lowering the temperature of the water, the rate of heat loss can be reduced.  Based on the above graph, if the temperature differential (between the hot water and room temperature) is dropped from 38°C to 22°C (i.e. the water temperature lowered by 16°C) then the energy loss would be reduced by around 1/3 and the annual saving would be around £4,000.

Condensing Boilers
It should also be noted that condensing boilers don't actually condense if the return water temperature is above 55°C, as this is the dew point.  If the return water is above 55°C then the boiler efficiency can drop by 10%.

Measuring Flow
It is fairly east to take temperature readings at the boiler outflow and return points and to measure the heat loss. The flow rate in the pipework system can be estimated based on the circulation pump specifications or can be measured using an ultra-sonic flow meter (we can rent you one of these).  All we then need to know is some basic details about pipe materials, pipe diameters, pipe insulation and expected water use and we can estimate the financial impact of heat loss and estimate the reduction that we could achieve by using the Aquadron system as an alternative to thermal treatment.

How the Aquadron Addresses Legionella and Reduces Heat Loss
The Aquadron treats all of the water that passes through the system, it does this by proportionally dosing all of the water with Anolyte, 24 hours a day, seven days a week. The Anolyte passes through the whole system, removing biofilm and killing bacteria, it even works in the shower heads and taps, at a point that is beyond the thermal mixing valves and that is not protected by thermal treatment. This ensures that Legionella colonies can not form in the pipework system.

Once the system has been disinfected it is possible to operate without the thermal barrier, this means that water temperatures can be reduced. This reduces heat loss and saves energy and money - the net effect is that you get improved water treatment with far higher levels of safety and energy savings pay for the system. 

Click here for more details on the Aquadron Legionella System.

Click here for project examples in hospitals and care homes.
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