Mechanical ventilation with heat recovery

asked 2015-11-13 11:49:58 -0500

AlaaAlf
31 ●3

updated 2015-11-13 14:53:58 -0500

__AmirRoth__

4436 ●5 ●17 http://bleedinggreenna...

Hi all,

I am modelling a building with 12 flats in it (existing building), with each flat having the following services:

1 central condensing gas boiler 88% seasonal efficiency
hot water central heating system with radiators
mechanical venilation with heat recovery, per flat, with dedicated MVHR units (Titon HQ1) in each flat, seasonal efficiency 80% (supply areas: sitting room, bedrooms; extract areas: bathrooms, kitchen)

Now I have been trying for months to model it in EnergyPlus following the example of (AirflowNetwork_MultiZone_SmallOffice_HeatRecoveryHXSL.idf) but with no luck..EnergyPlus comes really restrictive with how to build it..for some reason it should be a part of HVAC (or maybe I got that wrong), and I really struggled with getting around the fact that EnergyPlus requires supply and return nodes for every zone, when it is not the case of MVHR as it supply to different zones to the one that extract air from. Also there is no cooling or heating coils in my system, but apparently I cannot get away from energy plus without having them (as energyPlus won't accept uncontrolled unheated ducts)

Anyhow, I tried to attach a picture and attachment here..but since I am new I don't have enough points apparently. I would really appreciate any advice.

Thanks all

Alaa

answered 2015-11-14 05:34:45 -0500

Waseem

flag of United Kingdom of Great Britain and Northern Ireland

2522 ●4 ●18

updated 2015-11-14 05:57:10 -0500

@AlaaAlf : You can take two approaches to model HVAC system with no Heating and cooling coils;

1) Either you can define them and then you can set-up their availability to zero, meaning coils wont be in action even if there are modelled as part of your system.

2) OR You can make a typical air-loop system with no heating and cooling coils.

you can also select a high and low temperature set-points cooling and heating respectively so that it does not trigger HVAC system.

Regarding your other question: If I have understood it correctly, if you have only one MVHR that supplies air to all zones then you can model it as an Air loop -- supply and extract fans, heat exchanger (rotary, plate), which will supply and extract air from different zones. Is this what you are trying to model?

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Hi Waseem, Thank you for your comment. Actually I tried to e-mail you ob your Loughborough Email but it didn't go through. Anyways, I did try both ways, but the problem is, EnergyPlus expect as I mentioned to have a supply and return register, for every zone..and this is my main problem that the supply path is completely independent from the return path. Therefore I cannot create a loop which throws all sort of error in energyPlus. The MVHR supply to bedrooms and living room, and extract from bathroom and kitchen.. I appreciate of you have done it (because I saw your post) to show me how.

AlaaAlf ( 2015-11-14 08:19:47 -0500 )edit

Hi @AlaaAlf: I have left Loughborough University some time ago, currently working at Cardiff University. First thing, in EnergyPlus, supply and return air flow rates need to be equal. The second thing is, you may have to use the ZoneMixing object to transfer air from a 'source' zone to a 'receiving' zone -- meaning from living and bedrooms to bathroom and kitchen. My case was different, I modelled HRUs (heat recovery units) which were supplying and extracting air from same zone so no mixing was involved.