| Q: Which is better, flat plate or vacuum tube collectors? A: A well designed system using either collector will work equally well in most cases. In terms of efficiency the glazed flat plate collector is more efficient than vacuum tube at temperature differences up to approx. 40 degrees C (for example heating water from 10 degrees to 50 degrees) whereas the situation reverses for higher temperature differences. If there’s a particular application where high temperature efficiency is critical vacuum tubes would be favoured but for the temperatures used in domestic house holds collector type is usually not a significant design factor in system design. Back to Top Q: In a new house build is it better to integrate the collectors into the roof? A: Yes, it’s worth considering particularly in exposed locations. It may cost a little more but it makes sense from an aesthetic, durability and efficiency point of view. In-roof collectors are less exposed to the elements and most people would say they look better. There’s also the added advantage of the collector being better insulated. It’s not possible to integrate vacuum tube collectors but panels are usually fixed in place using stainless steel bolts so that a durable solution is still possible. Back to Top Q: How big should the hot water storage cylinder be in a solar thermal system? A: It should be large enough to cater for the needs of the number of occupants as well as having some reserve capacity for cloudy days. Example, a 4 person household. Taking a guideline usage of 50L per person per day the usage is 200L. Allowing half a day’s reserve this would imply a 300L cylinder and if a day’s reserve were to be allowed the cylinder would need to be 400L. (assuming system is designed to achieve 70% of total needs). There’s a trade off between the size of cylinder and panel area in that too much panel area in relation to cylinder size will result in excess heat generation in Summer and also a longer pay pack period. Having too little panel area in relation to cylinder volume means that it will take too long to achieve useful working temperature and the overall amount of energy that can be harnessed is reduced. Back to Top Q: What maintenance is required on a solar hot water system? A: Very little. A well designed and properly installed system will run for years with virtually no input from the user. It’s advisable to occasionally check the system pressure and perhaps have the glycol concentration checked annually but other than this there’s very little in the system that will require maintenance. For on-roof collectors an additional check would be to inspect the insulation of surface pipe work for degradation due to exposure to the elements, birds, etc. Back to Top Q: Is a heat dump necessary for periods when very little hot water is being used and it’s very sunny? A: All solar thermal systems generate too much heat in Summer but a well designed system will dissipate this energy without any intervention from the user. The best way to achieve this is by correctly designing the expansion circuit so that the pressure vessel can cope with liquid and gas expansion for all operational conditions. It’s also possible to fit a divert valve which will dissipate this unwanted energy through a radiator or other heating circuit but this usually unnecessary, as it increases the cost of installation and introduces additional complexity. Besides, this solution won't work when it's most needed, i.e during a power cut on a very hot day. Unless there’s a particular use this excess energy can be put to, it’s better to design the expansion circuit to cope with it rather than divert it to another source. Back to Top Q: For hard water areas, what effect does this have on solar systems? A: The solar circuit is not particularly vulnerable to lime scale build up as the transfer medium (solar fluid) contains a corrosion inhibitor, is designed for high temperature operature and is circulating in a sealed system, all of which reduce the potential for build up of deposits. However, as in any hot water system, the pipe work and storage cylinder are suseptible to lime scale build up and the most important control is to limit operating temperatures. Depending on water quality, it's also a good idea to consider fitting a stainless steel or glass lined cylinder if the site has a history of problems with copper cylinders. Back to Top | Airtightness is important: Plaster and floor should be introduced to each other as they really must meet! 
This is what happens when trickle vents are left closed in a bedroom and the occupant does not open the window. Part F of the building regulations is there for a reason! 
How well do you think the insulation has been fitted in the cavity? 
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