Is the heart (♡) also a traditionally Chinese symbol for love and compation, as we know it today - or is there any equivalent old symbolics in Chinese calligraphy?

Yes, the world love in chinese (愛) has the heart word (心) in the middle and the word heart (心）derived from ancient chinese pictograph that shape like a heart ♡.

Love （愛) is believed to emanate from heart from which a person admire and love another. The original word for love is 㤅, a phono-semantic compound (形聲, OC *qɯːds): phonetic 旡 (OC *kɯds) + semantic 心 (“heart”).

later 旡corrupted into 爫冖 ,with 心remain and additional 夊added at bottom to depict human, hence formed the traditional chinese word 愛.

https://youtu.be/BEiFlfUfkGI

The traditional Chinese word later evolved to 爱. Instead heart 心 it replace with the word friendship（友).

Chinese words semantic always depicting reality and the truth may be love:

1. no longer emanate from heart;
2. transcend the boundary of human.

Or

1. Maybe we discovered love is actually a result of hormone chemistry, nothing to do with heart.An

2. d such chemistry present in all living things for continuation of gene.  

3. Perhaps, friendship is more important to keep relationship going now.

Friendship indeed surpass love for survival in today context. In the dog eat dog world era now, it is how you can exchange benefit with another (friend) to form a mutual benefit relationship(friendship), with or without genuine affection or emotion(heartless💔).

Unconditional love seems to be a thing of past now!

What do you call a person who doesn't believe in god?

 Atheist don't believe in God. Agnostic don't bother about God although they might recognise the existence.

It is also very subjective as to whether the person's God refer to, nature, truth,and love, which not common in mainstream religion that conventionally set of rules, regulation and ritual. Such religion are like Shintoism and animalism is more spiritual and primitive.

How can I get sun light to the ground floor from the roof top of two floors house?

 This question is dealing with fenestration, opacity and room height.

Sunlight can penetrate second to ground floor via

glazing/skylight/glass block floor, (horizontal-opacity)

hammock/netting floor, (horizontal-fenestration)

steel grating floor. (Horizontal-Fenestration)

Void(fenestration)

Floor height in relative to solar path (vertical-daylight factor) and Window to Wall ratio (vertical-daylight).

Not only these allow natural daylight but also ventilation that can effectively reduce the consumption of electricity. Other than the above, passive design strategy to be considered in the design are site orientation and design of the building.

Of course, there's more advanced passive technology such as light tube. it need not be expensive fancy stuff. A plastic bottle with some chlorinated water will to the same tricks. Refer to picture below.

It is subject to designer preference and functionality of the building, budget and availability of materials and workmanship.

Some may design roof to be operable without glazing which common in small rural area.

Are Christians also kafir according to the Holy Quran?

 The Arabic word 'kafir' means infidel to God/disbeliever. God in Arabic pronounce as 'Allah', the only God. Any God can be called Allah as long as it is singularly (meaning one god/monotheism) but the definition of kafir clearly include anyone not belief in Islam and those Muslim that not act according to Islamism.

Although both Christian and Islam are said to be within Abraham tradition along with Judaism but they might pray the different God. There's great degree of plagerism from Islam to Christianity and Judaism. However, the fundamental differents between Islam and Christian are that Christian belief Trinity (one substance, 3 person) but Islam is one substance, 1 person). Jesus die for man's sin and that he is son of God is denied by Islam.

Christian can not be infidel to Islam because there's no privity for fidelity since Allah is clearly not the God Christian belief in.

Christian belief Jesus is son of God, not merely a messenger. It is Islam that infidel to Christian since Christian predate Islam by over four hundreds year and Islam is a fabrication with plagerism from Christian.

Kafir is used to intimidate Muslim who wanted to:

• leave Islam,
• those who refuse the insane command of jihad in the Quran
• Non-muslim that refuse to convert to Islam.
• Muslim who simply perform what his community deem unfit as Muslim.

This is tactic to use psychological and peer pressure to keep Muslim submit and pressure non-muslim to accept Islam (the leader of Islam).

It is a psychological game in which those who obey will be rewarded with paradise in after life and those kafir(rejector/disbeliever, infidel) will go to hell.

Nobody know whether Allah really exist or indeed he speak through angel Gabriel to Mohammed but everyone know Mohammed successfully hypnotised his followers to rage war and killing millions (270millions) of human life, since the inception of Islam. Hard earn money and wealth of others were looted, women were being enslaved as sex slaves and working maids. Non-believers are force to pay jizya. Clearly this is direct contradict to what Jesus have done:

• Jesus face his enemy despite knowing he will be killed (the last supper) vs Mohammed cowardly escape into cave.
• Jesus provide food to the poor vs Mohammed robbed Meccan caravan for food and rage war.
• Jesus never kill anyone and he forgive people vs Mohammed kill people who don't submit him.

None other religion other than Islam keep sex slave or any slavery at all. No religion ask their believer to commit violence and even kill others except Islam.

A rational mind would see it is Islam that infidel and severely distorted Christianity and basic humanity. However, it is indeed a very power ideology to manipulate and control others for their own benefits.