Effect of convector in comfort maps

Hi all,

I was wondering if someone can give me some advice on the following.

I’m working on a fully glazed building in a very cold city in Russia (exactly, very sustainable). So far, I have been using Chris’ comfort maps to show the impact of triple glazing vs double glazing in terms of comfort (due to radiant heat loss and downdraft discomfort).

Even with triple glazing people in areas next to the facade experience discomfort during winter (temperatures vary between -5 and -15 ºC during the typical winter week), so we need to install convectors below the windows.
I am trying to explore how to include the effect of the convectors in the calculations run by the comfort maps, though it is far from being direct.

I’ve come up with the following workflow:

  1. Run the energy model using an ideal air loads system, with a setpoint of 21ºC
  2. Use the surface temperatures to set up a buoyancy CFD model in which to include the convector below the window (I guess that it will take the air at room temperature and heat it up to, say 23ºC).
  3. From the results, we should be able to see the impact of the convector on the temperature distribution near the windows (how much does it change the air temperature near the window and what is the area being affected)
  4. The resulting air temperatures would then be fed into the comfort maps, for every point in space, together with the rest of the inputs coming from the energy model.

Probably this is not the most time-efficient or accurate process to do it, but so far I cannot think of any other way. Any comments on this are much appreciated.

Does anyone know any other way to show the effect of the convectors in the comfort maps?

Many thanks in advance,

Hi @RafaelA ,

I’d need to know a bit more about what you are trying to get out of the simulation workflow you describe in order to be of help. Typically, when you install convectors, you assume that the heat they provide will eradicate any chance of discomfort near the facade (you’re essentially heating the glass to room temperature). So there’s really no need to simulate them unless you are trying to answer the question of how large these convectors should be (or, rather, what heating capacity do they need to be sized to) in order to eradicate this discomfort. Answering this question really doesn’t require a CFD but rather a simple calculation of what the heat flow through the envelope is. That wattage of heat flow through the envelope should be the max wattage of heat supplied by the convectors.

The vast majority of the winter comfort tools that I have put on Hydra assume no perimeter heat elements (like convectors) because there are a lot of good reasons why you want to avoid them:

  1. Their expensive! - Way more expensive than the cost to upgrade from double pane to triple pane. If you can get rid of all the piping. boilers, and heating elements you need for such perimeter systems, you’ll typically save a significant chunk of the project budget, which can then be used in other aspects of the design.

  2. It’s not energy efficient - The least efficient location for a heating element within a building is the perimeter. You are essentially throwing heat right out of your building by warming the facade with convectors.

  3. It’s not a very elegant design solution - Perimeter heat is often “tacked on” in later stages and it typically isn’t seamlessly integrated into the design. It’s far more elegant to solve the issue with a better insulated envelope rather than tacking on another system to address the issue.

For this reason, if you are still itching to simulate something, I would encourage you to explore some other options for engaging the issue rather than trying to simulate convectors. For example, is there any way that you could put in a sill for your building without changing the view much but improving the thermal comfort? Or could you drop the window head height by a few centimeters and could that get you in the right comfort range? If all else fails, radiant slabs often get rid of thermal comfort issues and you can simulate these using the newly-revised winter comfort example with an energy model on hydra:
Just switch the HVAC system from “Fan Coil Units” over to “Radiant Slab” and you will see what I mean.

A heated slab is often a much more elegant design solution and it can still be low energy if the supply temperature of the water running through the slab is kept low and you source your heat from such low temp sources (like solar hot water or waste heat from other processes).

Let me know if any of this is helpful as I know I’ve gone a bit off-track from your original question,

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Many thanks for your reply Chris, I find your approach very valuable and I’m sure it will be very useful for many people around too.

What I had in mind was perhaps too complicated. Since the convectors are throwing hot air to the windows, I was wondering how would this heat affect the air temperature in those areas near the facade and the people sitting there.

However your suggestion makes much more sense and simplifies it significantly. Since the heat would directly go out of the space through the glazing, only the glass will be heated to indoor temperature. Probably, as the convectors wouldn’t be perfectly adjusted all the time, there would be some extra heat remaining in the areas near the façade but I guess it could be neglected.

As the team is keen on seeing comfort results for the final proposal (including convectors so far), I assume that replacing the glazing temperature for a constant temperature equivalent to the indoor air would do it. In terms of energy, it is a clever way to find the wattage flow through the envelope and assume that as the energy used by the convectors.

On another level, I definitely agree that perimeter convectors are far from ideal for all the reasons that you mention. However, in this particular case, it seems the way forward as the project is already in a late design stage and even with the triple pane they are required (the team is keen on a fully glazed facade). I am now curious on how much would be the changes you suggest affect comfort (I’ll try to test them as they could potentially be a great solution for other similar cases)

Many thanks for the suggestion of the radiant slab, it is amazing the pace at which Honeybee evolves and the possibilities it brings! As you mention it is a very elegant solution and might be the way to get rid of those convectors. Perhaps we can eliminate them in the overtime :smile: