HVAC simulation issue

Avik · May 6, 2018, 7:08pm

Hi, I tried to make a comfort simulation for my project but I wanted it to be a little bit more precise than “roughly”. To make it so I need reliable HVAC simulation. Despite working on it for a whole day I still get weird results. For now I used radiant floors and DOAS. The image underneath is with only heating attatched to HVAC component.

This is after attaching cooling and heating.

A that after finally attaching ventilation.

Thats how definition looks for now.

Adding ventilation makes a real hell from my apartment so I guess theres something wrong with… air temperature? Or maybe there’s not enough fresh air? However, without adding custom ventilation component the charts don’t look so good either. I have no idea what is wrong and how to “repair it”.

Also, for now I used radiant floors but at the and I’d like to achive something like capilary mates placed just above suspended ceiling. They look like that.

The thing is that I want to connect them to air sourced heat pump and use them both for heating in winter and for passive cooling in summer. Is it possible to make such combination in Honeybee or the best way will be through OpenStudio somehow?

mostapha · May 9, 2018, 11:59pm

What is the control strategy for ventilation?

Avik · May 10, 2018, 12:41pm

Well, target control strategy is that between -10 to 25C of outside temperature, ventilation is 100% working and if temperature falls out of those boundries, than ventilation is 50% working. And because there are troubles as you can see, I tried to minimalize number of factors that could mess with the results. And so I made it work always if the temperature outside is <30C so like… always. It’s always working, 100% through the year for now (because my first thought with overheating was that there is not enough fresh cold air).

chris · May 19, 2018, 2:03am

@avik ,
It looks like your availability schedules are probably messing things up and are shutting off the systen. Keep in mind that availability shedules are only on/off schedules and fractional values do not work with them. If you are trying to change the ventilation quanitiy, you should be using a ventilation schedule on the Set schedules component.

The most recent version of Honeybee has the ability to connect radiant loops to ground source heat pumps. I am not so sure how to model an air source heat pump this way since, even with the low temperatures of a radiant slab, most times when you try to generate hot water from air source heat pumps, the temperature Delta that you have to overcome to make the hot water makes it pretty inefficient. Is this slab in a really mild climate where there outdoors don’t get that cold?

In any case, you can start with the ground source template and maybe try editing that in openstudio to get the exact system that you are after.

Avik · May 22, 2018, 7:43pm

Yes, it was an issue with schedules. And I think I kind of solved it. At technical side, it not that tough or inefficient. It should be completly possible. Actually, the building I’m designing at the moment should be ready in the next year (in plans the foundation should be ready in fall in this year). Then I will be definietly sure how efficiently it does work. The setup looks like this: There is a air-sourced heat pump which is connected using two connectors to water tank. In water tank are two smaller, asymetrical tanks. Bigger one will be used to supply hot water to the building, the smaller one - to provide water for heating in winter and cooling in summer. It’s a really small building (around 100m2) so a small heat pump is planned. Something about 8-10kW. It should be completle sufficient. Important thing is that for heating with capilary mates you need water with temperature only around 30C so not that much. Next thing, as I mentiond before, those mates will be installed almost laying on drywall in suspended ceiling, so they won’t be covered in concrete or anything like that. I’ve been in a few buildings made like that, even big corporate buildings and setup like that is not only completle sufficient but also really cheap. And temperatures here in winter fall to -16C, in extremes during nights even -20C or -25C. Of course in temperatures like that such small heat pump is not enough so inside water tank there’s an electric heating coil which turns on when outside temperature is too low, so for no more than 20h during year usually.