Sanity check - heat loss calculator - Crooked Lodge

[BotusBuild]

I wonder if one of you kind heat loss gurus (who understands JSHarris wonderful spreadsheet) could do a sanity check on this for me.

The inputs part of the sheet are filled in thus:

 

and the calculated losses are as follows:

 

Am I correct to interpret the maximum heat loss to be the 2563W (January total daily heat loos for minimum OAT)?

Would a heat source rated at 3.5kW or 4kW output be sufficient to support that heat loss plus DHW, where I am thinking a UVC of 350 or 300 litres? Or should I go to a 5kW heat source?

 

Thanks in advance for your input

Edited March 15 by BotusBuild

[JohnMo]

Air changes per hour will be ventilation rate, so if MVHR with 0.3 or 0.5

 

MVHR hourly volume, did you add that figure, not sure where it came from, as it doesn't appear on my copy?

 

Not sure you your mean temperature make much sense, your coldest day is 5.3 degs, we had -9 for 4 days straight this year and last year.

[BotusBuild]

@JohnMo, thanks for the feedback..

The ACH figure I've left at 1, knowing it likely to be lower, but I have not had a test done yet. I jokingly said I need to meet or beat the 0.28 figure that Russell Griffiths achieved on his Nudura build 🙂 FYI - changing it to 0.3, changes the max heat loss figure from 2563W to 2331W, so I'm happy to err on the side of caution.

MVHR hourly volume - I just followed the guideline formula, but knowing that most of the time there will only the two of us in the property. Changing that figure seems to make no difference to the heat losses

The MEAN temperatures were taken from the Newquay, Cornwall weather station. The figures I found on the Met Office for locations closer to my site were a little higher, so I have erred on the side of caution, again.

1 hour ago, JohnMo said:

your coldest day is 5.3 degs

The figure is MEAN MINIMUM for the whole month of January. So, if we did have some -ve temp nights they will be offset by a majority of +ve temp nights in Cornwall 🙂 

Edited March 15 by BotusBuild
ACH 0.3 figures added

[JohnMo]

5 minutes ago, BotusBuild said:

knowing it likely to be lower, but I have not had a test done yet. I

Nothing to do with your air test results. It's how much your ventilation is moving in and out of the house, the figure is multiplied by the MVHR efficiency. For a leaky house you would add like 5 or 10% of your leak test figure to the air changes per hour.

 

6 minutes ago, BotusBuild said:

The figure is MEAN MINIMUM for the whole month

Your lowest mean is for the coldest day. The monthly average in this case is meaningless. You really need the historical average not this year's data also

[BotusBuild]

Not sure I understand that John. This is the definition of mean minimum temperature:

Averaging the daily low temperatures for any period results in a mean minimum temperature for that period.

 

The figures I have used are for Newquay for the period 2008 to 2023 (most recent full years data)

[Dave Jones]

try this calc instead, much more straightforward to use

 

https://www.changeplan.co.uk/heat_loss_calculator.php

 

 

[SteamyTea]

8 hours ago, BotusBuild said:

Or should I go to a 5kW heat source?

You may as well.

When I went looking  for a small ASHP, the smallest someone on here found was 3.5 kW.

Was same price as the 5 or 6 kW one, but it as unavailable.