Installation Of Solar Thermal Domestic Hot Water System Construction Essay

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The focus of this report is a feasibility study into the possible installation of a solar thermal domestic hot water system in an acute health care setting. The introduction of the UK's climate change bill has set a target of 80% of reducing green house gas emissions (GHG) by 2050 from the levels of that of 1990(HMG 2008). Currently the UK health sector spends a staggering £450 million on energy each year, the National Health Service (NHS) is responsible for emitting around 21million tons of CO2 per annum. This is more than some small medium sized countries for example Portugal (Health Estate Journal 2010) and is the largest emitter of GHG in Europe (SDU 2010). As the largest public sector organisation in the UK or possibly the world it is our responsibility to lead on carbon reduction. Therefore carbon emissions reduction has been acknowledged as a key objective within the NHS Carbon reduction strategy, Saving Carbon Improving Health (January 2010). Utilising this strategy the NHS has adopted these UK targets and established an interim reduction of 10% by 2015 using 2007 as a baseline from 21MtCO2 to 19MtCO2, and 34% reduction by 2020 to 13.86MtCO2. There is a need to adapt to change very rapidly implementing this Carbon Reduction Commitment (CRC). David Pencheon director of the NHS sustainability development unit stated (June 2010). "The key is definitely not to sit back and wait for others to make headway but tackle this commitment head on." It is far better to be part of the learning process. "Otherwise you risk both being left behind and potentially damaging your reputation and finances." The question now remains how these targets are going to be realistically achieved? Traditionally the majority of the NHS building stock dates back to the early 1900's ad hoc growth over the years have resulted in parts of the estate failing to meet the requirements of a modern and progressive health service. Many of these buildings also contain mechanical and electrical equipment which is at the end of its design life. Therefore updating systems incorporating renewable technologies is essential to bring the estate up to modern day design standards and to meet these increasing sustainability needs. The challenge to succeed is immense but achievable, with innovative creative design and forward thinking.

Meeting the challenge

As a public body and the largest organisation in Leeds, the Leeds Teaching Hospitals NHS Trust (LTH) has a duty to manage its resources and CO2 emissions in a responsible way. A comprehensive review of carbon emissions was completed these identified emissions are currently 70,910 tonnes. A plan has been devised which identifies opportunities for energy reduction to a level at which the Sustainable Development Unit and Government targets for 2015 will be achieved. The trust's carbon data can be found in Appendix 1. As part of this a number of measures have already been employed by the trust to reduce our total carbon foot print. They include;

Introduction of more energy efficient lighting in various areas throughout the trust.

Installation of more energy efficient boiler and controls at Chapel Allerton.

Participation in a Leeds City Council led feasibility to examine the benefits of a joint district heating scheme between LGI and the Civic & Town Halls.

Increasing staff awareness through a screen-saver switch it off energy campaign.

As seen from the list by its omission that solar thermal heating for domestic hot water services was not regarded at the initial review stage as a viable cost saving measure due to lengthy payback times and the need for a resilient hot water supply. However there is an argument for DHW supplies to be supplemented by solar thermal and that payback times should not be a restriction. There are substantial government grants available for these installations. Resilience of supplies and the controlling of legionella have to be carefully managed. This can be achieved by incorporating any solar collector system into the current building management strategy. Therefore it has been identified that one of the hospital wings may benefit from the introduction of this form of heating. A feasibility study will be instigated to demonstrate solar thermal hot water production is capable of supporting the hot water supply. During the study the aim is to convince both the trust board and other users of this possibility. The selected building is a large 1970's 9 story multi use hospital wing which currently is undergoing extensive mechanical and electrical refurbishment including the upgrade of the domestic hot water and heating systems also being considered. The hospital layout drawing in figure1 shows a proposed position of the solar panels. This area has recently had all the external AHU's removed as part of the extensive CSR ward upgrade scheme currently underway in the wing as seen in figures 2 & 3. Therefore due to the orientation of the building, this being North East to South West is a suitable position for a solar panel installation, an adjacent roof top plant room that will accommodate all the necessary ancillary equipment.

Figure 1

AHU's removed as part of CSR

Figure 2 Figure 3

Background

Solar thermal technology makes use of solar collectors by harnessing solar energy to heat hot water. The basic form of operation involves the transfer of solar irradiation energy in the form of heat to the solar circuit fluid (CIBSE AM10 2010). In the UK the amount of solar radiation per metre is approximately1000 kW·h annually and the peak solar irradiation is around 1 kW/m2 (CIBSE KS15 2009). This is also considerably less than on the equator due to higher latitudes. The UK also suffers from extensive cloud cover at various time of the year. This is mainly due lower angle of the sun on the earth's surface (CIBSE KS15 2009), below in Figure 4 is the typical annual average solar irradiation (kW·h/m2) on a 30° incline facing due south. Leeds is on the same latitude as Manchester therefore any calculations required will utilise the data for mean solar irradiation from the table in Figure 5 (CIBSE KS15 2009).

Leeds

Figure 4 Figure 5

Angle of inclination and orientation also impacts on the amount of energy a solar panel can absorb. The graph in Figure 6 below shows the various permutations of angles and orientation.

Figure 6

System sizing and selection

The Domestic Hot Water (DHW) in the building is currently split into 2 zones North and South; the North zone is supplied by two steam plate heat exchangers supplying. The South zone has two 25 year old shell tube calorifiers which are at the end of their design life. Hence the need for the study, hot water is circulated at 608C6 2.58C return design temperature is 508C to control legionella. Domestic Hot Water is stored in two vertical storage calorifiers with a capacity of 2000 litres each. The current storage system in the building was designed to handle a maximum peak flow rate of 4.2 litres /second and give a maximum hourly output of 8000 litres there would be no reason to change this requirement. However the storage calorifiers would be changed from single coil to twin coil vessels.

There is a possibility that a correctly sized solar thermal system may produce up to 60% of the annual energy needs to produce hot water (Renewable energy sources 2006). However 60% for this building is not practical due to the sheer number of collectors that would be required. A proposed 30% input to the building is highly likely or could be even greater dependant on the type of collector selected. This would supplement any new hot water system improving the trusts carbon footprint. The following calculations using manufactures data and known building data to approximately size both the solar thermal system and the new steam plate heat exchangers where carried out.

Storage vessel size = continuous flow rate (lt/s) x 0.25

= 8000 x 0.25

= 2000

Heat exchanger requirement Q=

Total heat required (kW/h) =

= 465 kW·h

As suggested a proposal would be to supply approximately 30% of the DHW for the wing to supply this there would be an additional requirement of 140 kW.hr from solar collectors. After consulting with various manufacturers' data sheets it was calculated that approximately 150m2 if flat plate collectors are used or 132 m2 of evacuated tube solar panels would be required to supply this amount of solar energy to the system. However more detailed calculations would be required before the scheme could be implemented. Therefore two companies were tentatively approached with a view of installing solar panels. Wellcroft Engineering one of the companies has already successfully installed 80m2 of solar panels at a Chesterfield hospital. The second company approached Future-Heating has also installed in Hanover the current largest solar DHW installation in the UK at 96m2. Thus proving that the use of solar panels to generate and supplement DHW is possible. The challenge will be to design and install the largest solar thermal DHW system in the UK. These companies have been requested to offer solutions to meet the trusts needs and budget. Solar collectors used in the UK can be categorised into the following two types as seen below in Figures 5 & 6 (CIBSE Guide L 2007).

Evacuated tube-collectors Glazed flat-plate collectors

Figure 7 Figure 8

Two possible solutions using both types of solar collector currently available on the market have been proposed. Company A has suggested one option would employ seventy Genersys 1450 (Vacuum) collectors. This is the only flat plate vacuum collector that is currently available in the UK. The total cost will be estimated at £225,000. The second option would be to use 80 Genersys 1000-10 standard flat plate collectors the cost was estimated at £240,000. The advantages and disadvantages of both systems can be seen in the table 1 below;

Genersys 1450 Genersys 1000-10

Advantages

Disadvantages

Advantages

Disadvantages

Outstanding performance

High standard of installation quality required

Small and easy to handle

Longer install times on very large projects

Highest solar gain per gross area

Re-evacuating required every 10-11 years

Excellent build quality and reliability

Small active area per panel

Small and easy to handle

longer install times on very large projects

Large range of mounting options

Excellent build quality and reliability

Horizontal versions available

Table 1

Company B has proposed that the use of Sixty five Viessmann Vitosol 100/200 F Flat plate collectors. The estimated total cost of around £275,000. The second option would be to use 44 Solfex CPC 18 evacuated tube collectors. The cost of this installation would be estimated at £215,000. The advantages and disadvantages of both systems can be seen in the table 2;

Viessmann Vitosol 100/200 F Solfex CPC 18

Advantages

Disadvantages

Advantages

Disadvantages

Very good build quality

Not very easy to handle

High performance

Parabolic reflector to maximise performance

Very heavy for aperture area

High performance

Limited range of fixing options

Higher performance in winter and cloudy days

Prone to stalling and overheating if not designed correctly

Horizontal versions available

More reliable than traditional vacuum tubes

Not recommended for schools without summer use

Table 2

Additional cost would be periodic maintenance to change the transfer fluid in the collectors this would be required every five years. All information regarding solar irradiation, panel efficiencies and panel outputs from the two proposals can be found in appendix 2. (CIBSE J).

Analysis of proposals

A final appraisal on the capital cost of replacement will be required before any final decision. However prior to this there are a number of considerations that require factoring into the costings. One of these factors is The Department of Health's Central Energy & Sustainability Fund of £100m (DOH 2007). This fund has been established to support energy efficiency and carbon reduction schemes across the NHS. The trust has previously secured grants from this fund to support the capital cost of other carbon reduction schemes. Therefore a substantial part of this particular scheme may also attract a similar grant a proposed request of £100,000 would be made to support the solar project. In addition to this there is the new Renewable Heat Incentive (RHI). This is a fixed payment scheme from the Government for renewable heat which is generated by sustainable means. The incentive was announced by George Osborne, the Chancellor of the Exchequer, in the House of Commons as part of the Government's Comprehensive Spending Review (HM Treasury 2010). The current grant will be replaced with a fixed payment, and will be paid each year for a period 20 years. A suggested sum of 18p/kW·h of renewable generated heat will be paid to each installation, although this has yet to be finalised. A direct comparison of all the proposals is shown in tables 3 & 4 in appendix 3.

Recommendations

Based on the study and the information given by installation companies it is technically feasible to install a solar thermal system in the block. The installation would be relatively simple as the majority of the infrastructure is compatible would only require minor alterations. The most effective solution would be Solfex evacuated tube system. This particular system including all grants has a payback period of 4 years. Continual gas price rises will ensure that this will be a shorter period. The CO2 savings amount to over 21 tons which is approximately 0.5% of the hospital wing total emissions. Given only this small CO2 saving if the Trust are willing to accept that the system presents a direct replacement for the current inefficient out dated system. The marginal additional cost required to payback, then a solar thermal system is economically viable.

Conclusion

The Trust is actively considering additional factors in a drive to achieve carbon savings within the estate and the potential benefits of installing visible renewable energy such as solar thermal hot water. There are other buildings within the hospitals infrastructure which would benefit from this type of installation. Although there are hurdles to overcome to enable us to move forward with the propositions factors such as size, cost and resilience are all potential stumbling blocks. However with careful planning all these hazards can be safely overcome. Once the installation has been commissioned and the payback time achieved the trust will receive free energy for the remainder of the installations life which is projected to be approximately 25 years. It is therefore essential that the trust embrace this technological challenge in becoming a carbon neutral organisation.

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