exactly how cold for the cold growing orchids

[golden]

HI!
I have several masdevallias and draculas,here is the lsit:
- Yungsun (Sun Dancer 'Yellow Doll' x yungasensis 'Bob'AM/AOS
- Masd. veitchiana x Tuakau Candy 'Preston'
- FF Flight of Fance = (Copper Wing x Masd. angulata)
- Antizana 'Dragon Lair' HCC x Masd. sanctae-inesae
- Cuzco Gold 'Ruth' x Dracula vampira 'John' 15S
- Heathii 'Golden Gate' AM/AOS x Copper Angel 'Highland' AM/AOS
- Rein Sun 'Big 'n Bold'
- Ferris Wheel 'Purple Passion'
- Harlequin 'Copperfield' HCC/OSCOV
- Rein Staal 'Sunburst'-
- Harlequin x Masd. torta 'Ace'
- Antizana 'Dragon Lair' HCC/OSCOV 32S
- Chaperana 'Nashville'
- (Masd. coccinea x exquisita)
- (Lemon Glow x infracta)'Peachy Keen'
Draculas:
-D.radiella
-D.diana
-D.lotax
-D.mopsus
-D.Houtteana
-D.Severa

The summer here is very hot.They survived this year because I managed to give them extra high humidity and constant air movement.But this is just a temporary decision. I will make a cool/cold orhidarium for the next summer. I am planning to use one of those cooling glass cases wгich they use in the shop when they need just to cool the food (it is not a fridge).
I will make changes ,of course... anyway... I am ьоиьса that I усвв keep the orchids too cool.
Which are the temperatures wich will keep them happy? Which is the minimal temperature wгich I must NOT go under? Usually the main problem with these orchids is keeping them too warm.I fear ,my problem will be quite the oposite
Thanks for the help