So I have an HTU21d, and it is apparently hardware and software compatible with the SI7021 according to this page:
[Compare DHT22, AM2302, AM2320, AM2321, SHT71, HTU21D, Si7021, BME280[/url>
Franck](Compare DHT22, AM2302, AM2320, AM2321, SHT71, HTU21D, Si7021, BME280)