Hello I am looking at the Emerson Cardigan Pattern from Twoofwands. It calls for using two strands of yarn but i am looking to make a spring sweater that can be used in an office when the air conditioner is on too strong 
by a twentysomething woman. Could I make the sweater with just one strand? I am thinking it would provide a looser knit. The pattern calls for size 17 US needles. Thank you for insight, I have difficulty imagining how something looks. Thank you in advance
This is a bulky or super bulky cardigan knitted at 11sts/4 inches. The pattern on the blog and the Ravelry page call for US 11 and 15 needles but you will figure that out when you knit a swatch.
You can certainly use a single strand of a bulky or super bulky yarn that will give you the 11sts/4" gauge. It’ll be a warm sweater in that yarn (or in the equivalent 2 strands of worsted).
Were you thinking to use the same yarn suggested but just one strand on the larger needle?
If you have already bought the yarn you could do a few swatches (or one longer one, place a marker or life line as needle size change to try out different sizes) and see if the fabric is as you expect, open and with lovely drape or holey and floppy. If it turns out you don’t like the yarn with the larger needle you could pick a different pattern that works on the gauge you like in that yarn.
I have worked yarns on needles bigger than called for and liked the result very much, the softer more open stitch is appealing to me, but sometimes it takes some modification of the pattern to make it work. You might get the same gauge or might not… and then will need to consider if it’s possible to make the size you need with the pattern. It’s certainly worth making some swatches to see how the fabric turns out.
It would be worth trying out a ribbed edge on the swatch too, finer yarn on larger needles can be a bit sloppy in rib stitch but you could change the stitch count and needle size of the ribbing if this was the case.
I’m not surprised you want a warm cardigan AC can be sooo chilly!