• lee121
In summary, the kw usage of the heat exchanger can be worked out by using the Primary and return flow rates, the flow meter fitted to the Primary return, the cost per Kw, the temperature rise due to the flow passing the heat exchanger and the Specific Heat of Water.
lee121
Can anyone tell me how to work out the Kw usage of a plate heat exchanger using Primary and return flow rates when no demand for hot water or heating is needed; assuming 0.04p per Kwh is charged.

Basically a valve is passing when the heat/hot water is off and want to work out the heat loss and costs incurred due to the valve passing by using the flow rate, flow/Return temperature and 0.04p Kwh cost.

assume the following:

• Primary flow rate to the plate is 80c and the return temperature is 79.5c.
• the flow meter fitted to the Primary return is registering 700 litres per hour passing from the flow back through the return
• the cost per Kw is 0.04p per Kwh
What else would I need to calculate temperature loss from the plate heat exchanger In Kw per hour?

I am trying to form a spread sheet in Excel and enter formulas to work out the maths and ultimately provide the total costs of losses due to this valve passing.

The spread sheet I have made up has all the data I think I need but for whatever reason it does not work and gives me some crazy figures.

Many thanks for any help provided

700 litres/hr is 700 Kg/hr mass flow .

Temperature rise 0.5 degC

Specific heat of water is 4.2 KJ/Kg/deg C

Therefore energy lost/hr = 700 * 4.2 * 0.5 = 1470 KJ .

1 KW = 1 KJ/sec

Therefore 1 KW - hour = 3600 KJ

1470 KJ = 1470/3600 KW-hr = 0.4 KW-hr .

Cost - not very much @ 0.04p/KW-hr .

You are getting very cheap electricity - can I run an extension cable across to you ?

Nidum gave you the actual values of the energy used by your system. However, heat exchangers are not 100% efficient. If you can actually meter the electricity you would then be able to determine your exchangers efficiency too and maybe improve that as well.

eMany thanks, I have entered your solution into a spread sheet and it works fantastic.To explain why I need the calculation is as follows.The heat exchanger holds 1.5 litres of static water at an average of 52c, this is like a small storage tank that feeds the hot water taps. In effect holds a bank of hot water to ensure hot taps reach the taps sooner. The same heat exchanger is heated by 22mm copper pipework, with a flow of hot water running through it at an average temp of 55c-60c to maintain the temperature within the heat exchanger.

The 22mm copper pipework and water content, are heated from an external gas boiler.I thermostatic valve set at 52c is fitted to the ‘flow 22mm copper pipework’ turning off the flow when the heat exchanger reaches the correct temperature.
On the Return pipework from the heat exchanger, back to the external gas boiler is a flow meter fitted that measures KW usage and charges per kw used.As mentioned, when the heat exchanger reaches temperature the Thermostatic valve closes, stopping the flow and in turn, stopping the kw charge per kw on the flow meter.However, the thermostatic valve has failed and the hot water flows around the circuit, through the flow meter and back to the return pipe to the external boiler, charging for hot water not being used.The calcs provided will work out how much money is lost due to this circulation through the flow meter that measures kw used.

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## 1. How do I calculate costs in an Excel spreadsheet?

To calculate costs in an Excel spreadsheet, you can use the "SUM" function to add up the values of different cells. For example, if you have a list of expenses in one column and their corresponding costs in another column, you can use the formula "=SUM(B2:B10)" to add up the costs in cells B2 through B10.

## 2. Can I use Excel to calculate costs with different currencies?

Yes, Excel has built-in currency conversion functions that allow you to convert costs from one currency to another. You can use the "CONVERT" function to convert between different units of measurement, including currencies. For example, you can use the formula "=CONVERT(B2,"USD","EUR")" to convert the cost in cell B2 from US dollars to Euros.

## 3. How can I format my costs to show decimal places or currency symbols?

To format your costs in Excel, you can use the "Format Cells" option. Right-click on the cells containing your costs and select "Format Cells." From there, you can choose the desired decimal places or currency symbol from the options provided.

## 4. Can I use Excel to create charts and graphs to visualize my costs?

Yes, Excel has various chart and graph options that allow you to visualize your costs in different ways. You can select the range of cells containing your costs and then click on the "Insert" tab, followed by the "Charts" or "Graphs" option. From there, you can choose the type of chart or graph you want to create.

## 5. Is there a way to automatically update my cost calculations in Excel?

Yes, you can use the "AutoSum" function in Excel to automatically update your cost calculations whenever you make changes to your data. Simply click on the cell where you want the total to appear and then click on the "AutoSum" button in the "Editing" section of the "Home" tab. This will automatically add the "SUM" formula to that cell, which will update whenever your data changes.

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