timespan and UTC

class TimeConversion
{
    public static TimeSpan LocalTimeSpanToUTC(TimeSpan ts)
    {
        DateTime dt = new DateTime(ts.Ticks).AddDays(1);
        DateTime dtUtc = dt.ToUniversalTime();
        TimeSpan tsUtc = dtUtc.TimeOfDay;

        return tsUtc;
    }

    public static TimeSpan UTCTimeSpanToLocal(TimeSpan tsUtc)
    {
        DateTime dtUtc = new DateTime(tsUtc.Ticks).AddDays(1);
        DateTime dt = dtUtc.ToLocalTime();
        TimeSpan ts = dt.TimeOfDay;

        return ts;
    }
}

I suppose I would load the TimeSpan into a DateTime, then get the universal time from the DateTime and convert it back again.

var dt = new DateTime( timeSpan.Ticks );
var utc = dt.ToUniversalTime();

TimeSpan LocalTimeToUTCTime(TimeSpan localTime)
{
    var dt = new DateTime(localTime.Ticks);
    var utc = dt.ToUniversalTime();
    return new TimeSpan(utc.Ticks);
}

A problem I found with a couple of the previous answers is that creating a DateTime from ticks results in a date/time such as 0001-01-01 04:00:00. If you're in a timezone with a positive UTC offset when the framework attempts to subtract say 10 hours it goes below DateTime.MinValue and while it doesn't throw an exception you end up with a TimeSpan containing 00:00:00 instead of the correct result.

The answer by Ali Sepehri.Kh gets around this underflow by using .AddDays(1) however because the date is always January 1 for areas that observe DST you can end up with an incorrect result. Because I was only interested in timespans for the current day I ended up using a modified version of Ali's code that uses the current date as the base and adds the TimeSpan to it:

public static TimeSpan LocalTimeSpanToUTC(TimeSpan ts)
{
    DateTime dt = DateTime.Now.Date.Add(ts);
    DateTime dtUtc = dt.ToUniversalTime();
    TimeSpan tsUtc = dtUtc.TimeOfDay;
    return tsUtc;
}

public static TimeSpan UTCTimeSpanToLocal(TimeSpan tsUtc)
{
     DateTime dtUtc = DateTime.UtcNow.Date.Add(tsUtc);
     DateTime dt = dtUtc.ToLocalTime();
     TimeSpan ts = dt.TimeOfDay;
     return ts;
}