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HEAT LOSS IN HOT WATER SYSTEMS CALCULATIONS

WATER TEMPERATURE Vs HEAT LOSS AND COST IN HOT WATER SYSTEMS

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This is exactly what the Aquadron does for hundreds of customers.

Energy loss from a hot water system can be calculated as **heat loss from the pipe system x the flow rate of the water that is circulated**. If you can measure or estimate these variables you can calculate heat loss and thus the amount of energy consumed.

It is then possible to estimate the energy savings that can be made if the water temperature is reduced.

(but read the information below first!)

Hot water flow (driven by pumps) occurs continually. Whilst flowing through the pipework the hot water loses heat energy to the environment.
The temperature loss on the way through the circulation cycle depends on -

- The size, age and insulation of the piping system.
- The temperature differential between the water in the pipe and the ambient air temperature around the pipework.
- The time that the water is in the pipe.

A high volume of water circulation coupled with a high temperature loss will result in a large energy demand.

Heat loss can be reduced in a number of ways, one of the simplest is to reduce the hot water temperature to reduce the rate of heat loss. The graph below shows the effect that temperature differential (the difference between the hot water temperature and the ambient temperature around the pipe) can have. As you can see, a 2" pipe will lose around 94 W/m if the temperature differential is 38° C, of the temperature differential is reduced to 22° C the heat loss will drop to 60 W/m.

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.

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%.

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.

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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