Revit MEP Space schedules - actual heating load

[rpowers]

I''m creating a residential model with a central heating system. I have the spaces set, and heating and cooling load calcs have been run and the results for Calculated heating load is shown in my Space Schedule.

My question is: What parameter type do i add to my radiators etc so I can offset the power as "actual heating load (W)" against my Calculated heating load (W). in the same way as the AirFlow in ducting works? The only heating load parameter type I can see falls under the HVAC discipline, is this where I should be looking?

Thanks

Rob

[dennis]

I will take a stab at this, though I admit, I don't quite understand the question.  You will need to work in the HVAC side of things.  The "Actual" value in the SPACE properties is what it sees as the total of the CFM values of the supply diffusers.  With no diffusers placed, there will be no value for "Actual".  And as a side note, the SPACE doesn't care if it is one big diffuser as opposed to 5 diffusers.  So your calcs should be within the SPACE and based off of these objects.

[rpowers]

Thanks Dennis,

I've uploaded a couple of images as I can't upload my revit model. The lounge has 2 radiators which have no effect on the loading in the schedule, (layout 1) where if I drag the diffuser into any room the schedule updates for the Airflow. (layout 2)

I'm not understanding the link that needs to be there for the power generated by the radiators and the calc'd value from Heat/Cooling Load Calcs.

Which parameter should i add to the radiator to give me a value in the Actual heating load column?

Thanks

Rob

[moby21]

Hi,

I am also relatively new to RMEP but I also assumed that the addition of a radiator would affect the space in the same way as the addition of a diffuser would i.e the heat output contributed by the radiator could be added to the amount of heat required. So far I have not found out how to do this.

The only thing I can add to this thread is my system 'hydronic supply' is showing a water temperature of 4 degrees. So I assume the answer, if there is one, will have something to do with the systems parameters?

[Martin__Schmid]

Generally, when you run a heating load calculation, only heating losses are accounted for... not heat gains.  Basically, the worst case condition that needs to be offset by the heating system. This is consistent with the methods perscribed in the ASHRAE Handbook Fundamentals.

If you want to take into account gains for internal equipment, such as the radiators you mentioned, you need to do a few things:

1. On Manage > MEP Settings > Electrical Settings > Load Calculations, check the box for 'Use calculations for loads in spaces'.

2. On the individual spaces, under Electrical Loads... Power, set to 'Actual', this will then tabulate the actual electrical load in the space.

3.  For the load classification of your electrical load, make sure it's 'Select the load class for use with spaces' is set to Power.

4.  When running your heating/cooling loads, make sure to check the 'Use Load Credits' option.

These radiators will now show up as a negative heat loss (that is a heat gain) in your Heating/Cooling loads report.  They will also show up as a heat gain in your cooling loads, which may not be desirable.

[rpowers]

OK, thanks but so this doesn't do what I want. I want to be able total the Power of items placed within a space in exactly the same way as adding multiple diffusers to a space does with Actual Supply Airflow.

The simple questions are:

When creating a space schedule, and add the field "Actual Heating Load" how do i get a value to appear in the column?

What parameter should be added to a family to place that value?

Thanks

[Lev97]

So you want a "power Delta" column like the "Supply delta" column?

[Martin__Schmid]

>> When creating a space schedule, and add the field "Actual Heating Load" how do i get a value to appear in the column?

You need to do step one in the list above... then, all electrical connectors with the Classification set to 'Heating' found in the space will be have their loads summed in the schedule.

See video:

http://www.screencast.com/users/MartinSchmidADSK/folders/Jing/media/76d2eaa9-3b08-4a85-8529-710db34a...

[moby21]

Hi, I don't want to hijack the thread created by RPOWERS but I think the advice given is talking about two separate things. The solutions proposed here would help solve the problem if the radiators were electric. But not for mechanical.

I assumed that most of the radiators used  have their heat supplied via hot water and not electric. Therefore any load must be generated by a boiler.

In a typical scenario, the max heat load to a space as calcuated by the software, might be say 10kW. To maintain the space at the design temperature one might have to add 5 radiators each emmitting 2kW.

If I read JPOWERS question correctly, (and if I do not then it is certainly my question), what value would I need to add to the radiator family in order for the schedule to take into account the heat added to the space by the hot water, to offset the design heat load required.

In summary, adding diffusers to a space allows for a certain air flow to be factored in. But adding radiators seems not to work in a similar way. It should do but I can't understand how to do this. Further more, adding radiators to a hot water circuit should allow the pipes to be sized and the boiler load to be given. But that might be a battle for another day.

[Martin__Schmid]

To address the question:

"My question is: What parameter type do i add to my radiators etc so I can offset the power as "actual heating load (W)" against my Calculated heating load (W). in the same way as the AirFlow in ducting works?"

It sounds like your goal is to verify that the total heat input of mechanical components in the space meet the Heating Load. You can do this with an Embedd Schedule.  See the attached project for an exmaple.

[GabrieleNovembri1027]

I'm sorry to come back again to the problem of radiators but, it seems, even in the 2013 version is not so easy to design the simplest kind of heating system:

A boiler with some radiators. It is not simple in other word verify that the heating power introduced with the radiators is adequate as required by thermal analysis.

The issue was highlighted long time ago and don’t seem solution have been given up to now!.

Using the words of Moby21:

"In a typical scenario, the Max heat load to a space as calculated by the software, might be say 10kW. To maintain the space at the design temperature one might have to add 5 radiators each emitting 2kW"

The solution proposed seems a walk around.

No news for this problem ?

Thanks

[Martin__Schmid]

Embedded schedules provide the information you are after... if you take a look my the prior posted example, it shows a space-by-space summary of the design heating load for each space, as well as a list of each mechanical equipment component and its associated heating output, with a sum.  So, for each space, you can see if the components in the space meet the load or not.

Perhaps you find this to be a 'workaround' because there is no built in tally for heat-output of elements placed within a space, as there is with the ability to tally airflows on a space.  I can see your point, as we never designed the software to facilitate the specific workflow you seem to be after... which is, to see the value populated 'automatically' on the Spaces.  There are at least a couple of reasons for this.  One, Mechanical Equipment is a rather generic category.  There is no internal mechanism for an element to indicate that it is a radiator, and what values it has for its heat input, output, efficiencies, etc...  Without an element knowing these details, there can be no built-in way to track the info you are after.

Two, there is a built-in mechanism to populate (shared parameters) and retrieve (schedules) the requested information that is in line with other similiar queries one may want to extract from the model, such as 'What is the total floor area required by Specialty Equipment in each Room' or 'What is the total cost of all furniture in each Space'?   By populating the model with the necessary params to track the type of equipment (radiator) and its output, you can extract the results you are looking for.

While there isn't built-in functinoality to address your specific model inquiry, Revit does provide generalizable tools to address the query and others like it.

[SFragtrup]

Is there a chance that the problem has been solved for Revit 2014?

I am troubled with the same issue. And embedded schedule is not the solution for the purpose. Can´t see why heating is supposed to be different from air supply and illumination?

Best Regards

Steffen

HVAC-Engineer @ MOE.DK