Solar water heating systems UK = Solar panels + UK solar energy. Solar thermal: solar power & solar hot water.
Solar thermal installations SAP energy calculations
Free Excel solar performance calculator available.
Of interest to solar installers, solar designers and solar engineers, Solar Twin Ltd have devised a free SAP (Standard Assessment Procedure – Solar Thermal Energy Performance Simulator) calculator for solar thermal installers as a simple excel spreadsheet. You can use it for any type of domestic solar heating installation. Like Solartwin, the SAP solar calculator is simple and easy to use.
You can quickly change all twelve SAP inputs, such as the size of the hot water store, the type of solar panel used, the hot water demand and whether the system is PV pumped or not. For your convenience, ALL the relevant SAP reference tables are included in the calculator. This lets you perform as many “what if” calculations as you want.
Your free SAP solar performance calculator includes two useful sets of default settings:
- one for a generic 3 sqm flat plate solar panel (settings which you can easily change to suit yourself)
- plus, to save you time, a pre-set Solartwin retrofit installation, suitable for to a typical retrofit to an existing domestic hot water cylinder.
Please just email hi@solartwin.com and ask now for your free SAP 2005 calculator.
Besides supplying free SAP software, Solartwin also supply solar water heating systems, design advice, and bespoke training packages. Do call us now!
Background:
SAP is actually a de facto standard, given its pivotal role in delivering numbers which are used in:
- Subsidy schemes such as Low Carbon Buildings Programme (LCBP) via the Microgeneration Certification Scheme (MCS)
- Building regs and Part L on Energy Efficiency
- Code for Sustainable Homes (CSH) and Energy Performance certificates (EPC).
Ther is a desirability of accuracy for a level playing field. As a de facto standard, it would be appreciated if the next SAP were to meet more closely general principles which are contained in BS 0′s (“The standard for standards”). These principles include:
- To take full account of the current state of technical development and
- To provide a framework in which innovation can be accommodated and supported.
Here are six ways to improve SAP.
They cover diagrams, HSE, stratification, dedicated pre-heat storage, effective solar volume and microbore pipes. I have also made six suggestions. I have tried hard to keep them as simple as possible. Having already been involved in the minute technical details of upgrading Polysun (to represent PV pumped solar thermal) I appreciate the challenges of introducing variants to SAP. So I hope the following is both practical and useful.
1 – Schematic diagrams.
It is noticeable that there is no thermal store shown in the SAP diagrams. Thermal stores are used extensively by ourselves (and by many others) in social homes, and nearly exclusively pre-feeds to combi boilers. In fact, thermal stores are the only plumbing solution which appear to be acceptable in a growing number of applications, including medical premises.
SUGGESTION 1 – Consider adding a thermal store diagram. (Maybe save space by possibly deleting some other diagrams, as discussed next.)
2 – Health and Safety Executive (HSE).
Every year there are deaths and several high profile Legionella negligence prosecutions under HSE’s guidance and CoP document L8. Fortunately none in UK have been attributable to solar.
Unfortunately, SAP figure H2 diagrams a-c, as they are drawn (no matter how you look at them) can not deliver full compliance with HSE Legionella L8 guidance’s para 158 “pack of four”, which is:
- Heat to 60C
- Heat it daily
- Hold it at 60 for 1 hr
- Heat the whole contents (including to the base).
Now let us look at point 4, the “whole contents” requirement.
All three diagrams (a-c) have in effect been described on the WRAS website (in a paper from a co-author of L8) as being “highly likely” to be creating a risk. Fortunately diagrams a and b can be adapted to comply, simply by the installation of a shunt pump, timed to come on at the same time as the heater.
But – adding a shunt pump is the equivalent, in design terms, to repositioning the backup heater down to the base of the cylinder, as is shown in diagram d. (This links in to the section on effective solar volume.)
Since diagram c has no heater, it is inherently noncompliant, given that flow rates through combi boilers rarely meet the length of time/temperature combination which is required to kill >99% of the bugs before they leave the taps. Indeed, over a year ago WRAS de-listed some combi-pre-feed systems with plumbing similar to this.
SUGGESTION 2 – Consider deleting some, or all, of diagrams 1-3.
3 – Stratification benefits.
Stratification is particularly important with direct heat in systems. These include type d and thermal stores (which are not illustrated).
Poor stratification happens when solar heat is delivered indirectly to the base of a cylinder via a heat exchanger.
Good stratification happens with systems where the heat is delivered directly to the top of the store. Thus the base is kept cool. So there is more pump on time.
Here is an illustration, with both stores having the same stored energy.
- Cylinder A average temp 40C. Top 45C, Base 35C.
- Cylinder B average temp 40C. Top 55C, Base 25C.
When solar panel is at 30C. Only cylinder B can collect its heat. Stratified cylinders have more “pump on” time. This boosts performance.
SUGGESTION 3 – Could SAP include a binary option (Eg, Heat exchanger: Y/N) where systems with no heat exchanger are properly credited with a typical X % better performance?
4 – Dedicated pre-heat storage diagram.
Dedicated pre-heat storage is not a generic concept but one which is particular to systems with raised heat exchangers.
SUGGESTION 4 – use a generic diagram instead.
5 – Effective solar volume.
This presupposes a single mode of operation of solar thermal but in fact there are other valid modes such as evening backup heating. The value of 0.3 for effective solar volume seems too low for operational circumstances where the backup heating is off during the day, but regularly heating to the base in the evening. It is not clear whether this approach is explicitly covered in SAP. The figure of 0.8 is suggested by TUV NEL, whose report has already been supplied. For example if a 120 litre cylinder were heated to 60C and the equivalent of 24 litres worth were to remain at sunrise, this would be an 80% allocation.
Obviously the principle of users controlling their energy use (and the timing of it) effectively is well accepted. Acceptance of this principle in SAP spans across non-automated activities such as doors and windows being kept closed on cold days to automated control such as central heating being turned down at night. The timing of solar backup heating is also automated, typically by setting the boiler controls on system commissioning. So a good user compliance can be expected and it does not depart from existing SAP assumptions.
SUGGESTION 5 – Could SAP please explicitly accommodate installations where the specification of the system requires different timing such as the backup heating to be off by day and on in the evening? Perhaps there could be a 3-way option such as: Backup heating: 24/24 or evenings/24 or continually off. This, perhaps coupled with an adjustment of the 0.3 figure in line with the 0.8 recommendation, could address the 10% or so performance handicap which is currently inappropriately applied to this type of operation.
6 – Microbore pipes.
Increasingly, solar thermal designers such as Solartwin are seeking to minimise “distribution heat loss” by using microbore pipes. Microbore pipes reduce distribution heat losses due to (a) <50% less surface area and (b) having <25% of the dead leg volume. Sometimes combined with the use of with water as a heat transfer fluid, (water has a sixth of the viscosity of antifreeze) simulations show that microbore pipes can deliver 5-10% extra energy to the store.
SUGGESTION 6 – Could this please be recognised, perhaps by having two or more different constants for (a) normal and (b) microbore pipes?
Impress your friends! Ask for your free SAP 2005 solar water heating performance calculator! Just email hi@solartwin.com now.
