IES-VE User Forum

Hi all. I have recently completed my e-training for VE-DSM and VE-SBEM, but in doing a couple of models based on real cases I am unsure if I am modelling /representing the heating services Apache systems correctly, particularly for VRF systems etc.?
In this case, the systems are as follows below - please advise if I have selected the NCM types correctly for these ? /and are there any other issues with my selections>? I would greatly appreciate any comments and overview as i wish to ensure that a model failing compliance is purely due to design rather than system input errors.
many thanks
Michael

1. Main system to GF - air source heat pump > underfloor heating
Mitsubishi ECODAN W140 FTC2 System
• Heating tab:
o NCM: Water loop heat pump (is this correct?)
o Heat pump electric: air source
o Fuel type: electricity
• Cooling:
o Pack chiller: air cooled (is this correct?)
o Pack chiller power: up to 100kW
o Chiller fuel: grid electric
o (is this correct?)
• System ductwork – assumed none. (is this correct?)
• Ventilation as part of this – assumed none. (is this correct?)

2. Main system to FF - VRF air conditioning
(system name specific data awaited from M&E contractor)
• Heating tab:
o NCM: Constant volume system (variable fresh air rate) (is this correct?)
o Heat pump electric: air source
o Fuel type: electricity
• Cooling:
o Pack chiller: air cooled (is this correct?)
o Pack chiller power: up to 100kW
o Chiller fuel: grid electric
• System adjustment tab:
o Should I assume typical for Ductwork to be leakage tested? [would it meet CEN classification A / or better?) (is this correct?)
• Ventilation:
o Assume no heat recovery ?

3. system - gas boiler to kitchens/WCs with HW cylinder
o Central heating using water: radiators for these areas
• Metering
o Provision for metering assumed yes.
o Warn of out of range value? Assumed no.
• System controls
o Central time control (only, assumed yes)
• Set point:
o mains cold inlet temperature 10 degs C assumed
o hot water supply temperature 60 degs C assumed
• storage system
o 250 litre (Telford Tornado cylinder as defined
 Storage losses checked as 0.0108 kWh/l.day
o Assumed no secondary circulation.

Hi Michael

Although I normally use DSM, the system set ups are very similar to SBEM inside IES so I think I can comment here.

1.
I am a little confused as to why you would have an underfloor heating system combined with air conditioning. How is the cooling being delivered? Normally cooling would be delivered via an FCU which would then also do the heating plus the cooling would then be provided by the heat pump as opposed to a chiller. The system type should represent the delivery mechanism of the conditioning into the space, so something local like a fan coil system or underfloor would be a better NCM choice I think. Without more details it is difficult to comment further.

2.
NCM constant volume is not the right system here because that will create a huge aux energy load, I suspect fan coil or split/multi-split would be more appropriate. Also, again I think the pack chiller type should say Heat pump (electric).

3.
This looks a little more logical than the other two but I would recommend having a totally separate system dedicated for the DHW since that is normally neater.

Generally it looks as though you have not quite mastered some of the subtleties of the system side of the SBEM and are getting a bit confused about how your system is supposed to work (since you are asking us whether your system has heat recovery... you need to find out!)

At the risk of sounding blunt, I would recommend that you get your head around exactly how the systems you want to model are actually supposed to work and then you will be in a better position to move forward.

CP

something that might help with this is the SBEM definitions of each of the system types available under NCM, you can get this from Table 13 in the latest version of the iSBEM User Guide http://www.ncm.bre.co.uk/

It is very much about considering the type of system you are trying to represent and then choosing the NCM system type that most closely matches, areas to consider would be heat source, delivery method, is cooling present and vent mechanism, central or local AHU and then there are some additional inputs on top of that, of course your efficiencies under Compliance are the most important input but as previously mentioned here a big consideration will be the auxiliary energy which is a direct result of your choice of NCM system type, the NCM Modelling Guide (pg 24 onwards) details the Aux energy calcs for the Actual Building, an area of particular interest is the fan power eqtns.

Not sure if anyone else could point us in the direction of any useful resources for getting up to speed with modelling systems in simulation software? I do see this kind of uncertainty come up fairly regularly so maybe this will help.

Phil

PCully wrote: ...Not sure if anyone else could point us in the direction of any useful resources for getting up to speed with modelling systems in simulation software? I do see this kind of uncertainty come up fairly regularly so maybe this will help.

Just popping back to this post - if there are any such (hopefully concise!) resources available, it would still be very useful. Not being a mechanical engineer myself, I recognise there is an risk for inadvertent error otherwise.
cheers, Michael

Hi,

As Phil suggested, in the iSBEM user guide there is a brief description of all the system types. I make it table 7.

That would be a good starting point. When I was getting up to speed with this, I would send the list to the mechanical engineer for advise.

Although there is a huge list of systems, I find many of them are very rarely used.

I hope this helps.

Ross