Monday, September 5, 2011

Solar Charging for Office building

This view is from the south
4 Sept 2011: I had an interesting approach from the prospective purchaser of a 6 storey office building, nearby. The building is 1960s, with single glazing, the original boilers (gas), some very inefficient perimeter radiators. On the plus side, it has a sound concrete frame, the windows are sound, it doesn't leak.
     The tallest part, the core with lifts, stair and boilers and mobile phone masts are all at the south end, but there is unshaded surface at the north end. There are two storeys of shops below the 4 storeys of offices. There is an car park on the west side.


He has the idea of eco-renovating it, with boiler replacement and insulation. Having visited my house and discussed heat pumps and solar charging, and all that goes with it, we have prepared a plan for improvement of the building, and for making it very energy efficient, if not carbon zero altogether, expanding the technology of the Peveril Solar house to be applied to an office building.
   This would include about 120 sqm of PV array on the roof, 50 sqm of solar thermal panel charging a cluster of boreholes in the car park below, two replacement ground source heat pumps for the original boilers (pipes all using the existing vertical ducts). We would also be able to dump summer heat gains of the building into the ground, either with different boreholes, or perhaps sufficient for it not to require solar panels at all!
   The windows are single glazed but in good condition, so could be upgraded with a programme of secondary glazing, floor by floor, and the small area of walls below the windows can be insulated internally. The roof element can be insulated with an inverted roof method. With such improved insulation, there is a risk of heat gains that will have to be dealt with, e.g. by underground thermal charging.
   I have suggested taking down the suspended ceiling to use the floor slab as thermal flywheel, and instal a number of zonal MVHR units as there are currently no ventilation ducts. ('Warehouse chic' ?). There are acoustic problems with and exposed slab, but one can suspend absorbers in the air space that allow thermal air circulation.
   I need to do some before-and-after heat loss calculations so see if the combination of insulation, PV, MVHR, solar charging and GSHP would get close to the ideal of zero carbon. It would be wonderful if we can!

Postscript October 2011: We have a PhD student in the school ready to take this on as a practical case study, his main topic being the enveloping of office buildings as a retrofit measure. He is more interested in the insulation and re-glazing than in the heat pumps. 

2 comments:

  1. David,

    another interesting one... some points come to mind straight away:

    How do you intend to insulate, internal or external? external good for retaining the thermal mass, internal serious consideration must be given to the thermal bridge detail and the dynamic interstitial condensation risk.
    I would suspect that when insulated and occupied then the building would require very little heating compared to the cooling requirement due to the internal gains. Of course in this situation the reversible heat pump would be recharging the ground. Care must therefore be taken in the balance of the ground loop design - recharging the ground would be a detriment to the efficiency of cooling. A TAS model would be good.
    Depending upon the renovation budget, I would give thought to a 3 pipe vrf air conditioning where the heat can be redistributed around the building by means of the refrigerant i.e. you will have cooling and heated zones in the building at the same time... this one of the most efficient ways of shifting heat around the same building. The excess of heat or coolth is taken up by the borehole array.
    In an office situation with annual heating and cooling loads a full assessment (without any recharge in most cases will actually lead to less number of boreholes than say a heating or cooling only system i.e. the ground acts more like an energy buffer.
    So in essence what you will find with recharge in this situation is that heating the ground in the summer is likely to reduce the efficiency of cooling.
    As you insulate it is likely that the building will become much more airtight. In that case there is a greater need for some sort of new ventilation regime - this is likely to be mechanical and as you say MVHR is the way to go. The option here is do you have a separate ventilation system or do you combine this with the heating system? i.e. have a full blown air heating system rather than the vrf air con option...
    I see that radiators are currently used. For the use of ground source on this scale it needs to be done in conjunction with a heating system retrofit - as i say either full vrf or air blown for highest efficiency or underfloor heating - but its the first two options are reversible for heating and cooling with the same heat pump.
    Potentially a full air blown system may be good as for large parts of the year advantage could be made of free cooling by increasing the amount of ventilation from the outside. (with consideration given to the humidity levels though - too much air could dry the air out.)

    oh i see - just noticed you say internal insulation... serious consideration here to the cold bridging to exterior wall at floor levels and around windows.

    Chris

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  2. Thanks Chris for your wonderful comments.
    I will try to get DA (the client) to include you in the team if the purchase goes through, assume you are still available as a consultant. (Id love to hear more about how the Solar Focus panels have performed at RB's place)

    Ive passed them on to him, and will reply to yours when I can (currently, I have to get my motorbike to garage for MOT and service, sorry that its not an electric one!)

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