Tubes per panel manifold

[Chris G]

I recently attended the one day solar installation course - which was exellent by the way, and on reviewing my notes later, came up with the following question, which I don't think cropped up on the day.

The course notes give a fomula for calculating the number of tubes (presumably each 47mm dia x 1.5m long?) required for a given capacity of hot water cylinder. However, there is nothing specifically mentioned regarding standard manifold sizes for accomodating these tubes in a panel, which would be another factor in sizing a system. I presume there are standard manifold sizes, and these are not made to order? I see 20 & 30 tube panels mentioned in the Web site, so I guess these are two standard sizes, though there is also reference to a 10 way version in this forum. Please could someone clarify this for me. Thanks.

Furthermore, if there are standard manifold sizes, when calculating the number of tubes required by a cylinder, is it better to round-up or round-down to the nearest manifold size?

[James Thorn]

Hi Chris,
 The manifolds available come in three sizes, 10,20 and 30 tube widths. For working out Kwh's they produce you can take the 20 tube figures and add or detract 50%. As for working out panel size to cylinder size it is a good idea to work out the hot water needs of the customer, then if they are happy with a good performance from April to September or if they wish to maximise it for a good performance from March to October.
 A customer recently had a 170litre system fitted with 20 tubes. Actual water temps in the cylinder reached 58c in June with them dropping to 40 in April and probably the same come September. My calculations predicted this but also showed that if he chooses to add 10 tubes or indeed had thirty in the first place then April and September  would  reach 53c and June would get to 80c daily. This makes the system a concern if left for a couple of days, let alone a week if no provision for a heat dump is not included.The 30 tube system would extend its life into March and October with 36c as opposed to 28 with 20 tubes. ( These figures will vary due to individual homes,roof direction,pitch and the chimney casting a shadow after 5o'clock as in this case.)
    If you have decided on a cylinder size I could give you an idea of temps to expect.Hope this helps James.     

[Chris G]

Thanks James - that's helpful information.