Modellling Mechanical Venilation with Heat Recovery

[burly]

HI all,

I am doing an energy rating using the ve-compliance module within ies v6.1.1. for a 5000m2 healthcare building.

Architect is wanted central heating using radiators (gas) in all of the building, and mechanical ventilation with heat recovery in all occupied offices/meeting rooms/treatment rooms etc.

He is expecting that the MVHR will reduce the energy consumption in the room since in theory the heating load will be less in those rooms, and therefore the heating demand from the natural gas system will be reduced.

But when modelling this, It is affecting the energy consumption in a significantly negative way.

I am setting up two Apache systems, one 'central heating using radiators', and one 'central heating using air distribution'.

The 'air distribution' option allows me to enter heat recovery information, i.e thermal wheel and efficiency.

I name the first system 'natural ventilation' and the second 'mechanical vent HR'

I then assign these tow systems using the group attributes option.

Just wondering am I going about this the right way. I want to be sure I am modelling the MVHR correctly.

In your experience, by adding MVHR to the building, should that reduce or increase energy consumption?

Thanks

[RossThompson87]

Hi,

Seeing as you are using v6.1.1. I assume you are doing a Part L 2006 model. I haven't done one of these in a while so my comments may not be 100% accurate.

I think the problem you are having is to do with the auxiliary energy.

A key decision factor on choosing a system is what provides the majority of the heating load. This is explained in the NCM modelling guide and I believe the equations are similar between 2010 and 2006 regs models.

If it is radiators you should stick with 'central heating using water: radiators'. Otherwise you will end up with unrealistically high auxiliary energy associated with air heating systems.

However with this system the wizard doesn't allow you to put heat recovery (in IES v6.1). Once you have competed the wizard you can directly input the heat recovery effectiveness on the main window.
You can then apply zone level SFPs to represent your MVHR unit.

By the time you get to later versions of IES it allows you to put heat recovery on the radiator system through the wizard. So I guess a bug has pushed you down the route of the choosing the wrong system!

I hope this helps.

Ross

[Complex Potential]

What Ross said.

By selecting "central heating using air distribution" you are telling the model that the heating is being provided centrally via an air system which is having to be blown around the building before entering the space which is heavy on fan power. In essence, you were not comparing apples with apples.

[burly]

Hi,



However with this system the wizard doesn't allow you to put heat recovery (in IES v6.1). Once you have competed the wizard you can directly input the heat recovery effectiveness on the main window.
You can then apply zone level SFPs to represent your MVHR unit.

Ross

Thanks Ross, when you say I should be able to input heat recovery effectiveness in the 'main window' do you mean exactly?
Do you mean this window here?


And then to apply zone level SFP's, would I need to add these individually under room using query tool like so?



Appreciate you taking the time to reply to my query.

Thank you

[RossThompson87]

Hi,

Yes that is exactly what I meant by the 'main window' and under heating system there is an option for 'Vent. heat recovery effectiveness'

Also the room query tool is how to apply the zone level SFP.

Are you doing the simulation in DSM or SBEM?

By the looks of your screenshot you are using the SBEM engine and this allows you to enter heat recovery on the zone level (using the room query tool). For DSM you enter it on the system level.

I imagine that the SBEM engine will take account of the heat recovery entered at the zone level rather than in the 'main window' at system level.

I'm possibly being dragged slightly out of my comfort zone here is as 90% of my recent work has been on 2010 Part L projects done with DSM.

In any case, you should be able to apply heat recovery with the radiators system and get the sort of result you are hoping for.

Ross